Distribution System Design For Smart City

FA C U L T Y O F E N G I N E E R I N G
Department of electrical
Power &Machine
Distribution System
Design For Smart City
Prepared By,
Ahmed Gomaa abd El-rahman

Ahmed Rizk abd El-latef
Ahmed Ali Moustafa El-mandarawi
Ahmed Ezat Mohamed El-said
Dalia Talaat Mohamed
Eman Atiya Boktor
Eman Adel Ahmed El-shamy
Hend Mahmoud Ahmed Amer
Karim Mohamed Hassanin
Kaoud Mohamed Hassn
Radwa Hamdy Anwer
Shahenda Ahmed El-saay
Distribution System Design For Smart City
Acknowledgment
We would like to express our gratitude for everyone
who helped us during the graduation project starting
with endless thanks for our supervisor Prof Dr. A.A
Salam, Dr. Azza ELdesouky Salam who didn’t keep any
effort in encouraging us to do a great job, Eng. Mai El-
adany monitoring and providing our group with valuable
information and advices to be better each time. Thanks
for the continuous support and kind communication
which had a great effect regarding to feel interesting
about what we are working on. Thanks are extended to
our project leader for beneficial lectures and his effort to
help members team.
Electrical minds team

Content
Chapter (1)
Introduction
1.1Introduction---------------------------------------------------2
1.2 The scope of the project------------------------------------------2
1.3 objectives of the project----------------------------------------------3
Chapter (2)
Primary and Secondary Service and System
Configurations
2.2Types of Sub transmission lines--------------------------------------7
2.2.1 Radial circuit arrangements in commercial building-------8
2.2.2Radial circuit arrangement: Common primary feeder to
Secondary unit substations---------------------------------------------9
2.2.3 Radial circuit arrangement: Individual primary feeder to
Secondary unit substations-------------------------------------------10
2.2.4 Primary radial-selective circuit arrangements--------------11
2.2.5 Secondary-selective circuit arrangement (Double-ended
substation with single tie) -------------------------------------------12
2.2.6 Secondary-selective circuit arrangement (Individual
substations with interconnecting ties) -----------------------------13
2.2.7 Primary- and secondary-selective circuit arrangement
(Double-ended substation with selective primary) --------------14
2.2.8 Looped primary circuit arrangement----------------------15
2.2.9 Basic spot network--------------------------------------------16
2.3 Type of Substation bus scheme-----------------------------------18

3.3.1 Single Bus scheme--------------------------------------------18
2.3.2 Double Bus, Double Breaker scheme-----------------------19
2.3.3 Main and Transfer Bus scheme------------------------------20
2.3.4 Double Bus, Single Breaker scheme-----------------------22
2.3.5 Ring Bus scheme----------------------------------------------23
2.3.6 Breaker-and-a-Half scheme---------------------------------25
2.4 Comparison of Configurations---------------------------------26
I

Content
Chapter (3)
Load estimation
3.1 Introduction-----------------------------------------------------------29
3.2 Description of the project land-------------------------------------29
3.3 consideration of load calculations---------------------------------31
3.3.1 Diversity factor----------------------------------------------------32
3.4 Load calculations of buildings-------------------------------------33
3.4.1 Building (13A) ---------------------------------------------------33
3.4.1.1 Calculation of flat load---------------------------------------33
3.4.1.2 Calculations of the total building loads--------------------33
3.4.2 Building (13B) ----------------------------------------------------34
3.4.3 building (10C) -----------------------------------------------------35
3.4.4 building (5) --------------------------------------------------------36
3.5 Load calculation of blocks------------------------------------------36
3.5.1 Block (1) --------------------------------------------------------36
3.5.2 Block (2) --------------------------------------------------------37
3.5.3 Block (3) --------------------------------------------------------39
3.5.4 Block (4) --------------------------------------------------------39
3.5.5 Block (5) --------------------------------------------------------40
3.5.6 Block (6) --------------------------------------------------------40
3.5.7 Block (7) --------------------------------------------------------41
3.6 Critical loads---------------------------------------------------------41
3.6.1 Critical loads of block (1) ------------------------------------42
Chapter (4)
Renewable Energies
4. Introduction -----------------------------------------------------------47
II
4.1Wind Energy----------------------------------------------------------48
4.1.1 Basic principle of wind energy--------------------------------48
4.1.2 Wind Turbines---------------------------------------------------48

Content
4.1.3 Types of wind turbines---------------------------------------48

4.1.3.1. horizontal-axis wind turbines--------------------------48
4.1.3.2vertical-axis wind turbines----------------------------48
4.1.4 Parts of a Horizontal Axis Wind Turbine-----------------49
4.1.5 Types of Generators used for Wind Turbines------------50
4.1.5.1 Induction Generator-------------------------------------50
4.1.5.2 Permanent Magnet Alternators------------------------51
4.1.5.3 Brushed DC Motor--------------------------------------51
4.1.6 Modeling the Power Generated by a Turbine------------52
4.1.7 Wind power system------------------------------------------53
4.1.7.1 Fixed speed wind turbine------------------------------53
4.1.7.2 Variable speed wind turbine--------------------------54
4.1.7.3 variable speed wind turbine with DFIG-------------54
4.1.8 Control Methods----------------------------------------------55
4.1.9 Advantages of wind energy---------------------------------57
4.1.10 Disadvantages of wind energy----------------------------57
Turbine technical specification------------------------------------59
4.1.11Power calculation--------------------------------------------60
4.2Solar energy---------------------------------------------------------61
4.2.1Insolation and Total Solar Irradiance-----------------------61
4.2.2Photovoltaic cells----------------------------------------------62
4.2.3PV connection--------------------------------------------------63
4.2.4Types of cells---------------------------------------------------64
4.2.4.1Crystalline silicon----------------------------------------64
4.2.4.2 Amorphous silicon--------------------------------------64
4.2.5Two approaches for using PV’s: stand-alone and grid
-Interface---------------------------------------------------------------65
4.2.5.1Stand-alone system----------------------------------------65
4.2.5.2Grid-interface system-------------------------------------65
4.2.6Steps in designing a PV system-----------------------------66
4.2.6.1 Calculate the Electrical Load-------------------------66
4.2.6.2Sizethe PV System------------------------------------67
4.2.7PV Subsystems – Inverters, Controllers, and
Wiring Inverters------------------------------------------------------67 III
4.2.7.1Charge controllers----------------------------------------67
4.2.7.2Wiring------------------------------------------------------67
4.2.8MountingPV panels-------------------------------------------68
Content
4.2.9Batteries-------------------------------------------------------69
4.2.10PV Output Power-------------------------------------------69
Power calculation of pv system----------------------------------71
4.3.Electrical Energy Storage Systems---------------------------74
4.3.1Electricity and the roles of EES---------------------------74
4.3.2Emerging needs for EES-----------------------------------76
4.3.2.1More renewable energy, less fossil Fuel---------------76
4.3.3The roles of electrical energy storage technologies----78
4.3.3.1The roles from the viewpoint of a utility------------79
4.3.3.2The roles from the viewpoint of consumers--------80
4.3.3.3The roles from the viewpoint of generators of
renewable energy---------------------------------------------81
4.3.4Types and features of energy storage systems-----------81
4.3.4.1Classification of EES systems-----------------------81
4.3.4.2 Mechanical storage system------------------------82
4.3.4.3Electrochemical storage Systems----------------82
4.3.4.4Thermal storage systems---------------------------83
4.3.5Configurations of EES-------------------------------------83
4.3.5.1Off-line systems---------------------------------------83
4.3.5.2Line-interactive systems------------------------------84
4.3.5.3On-linesystem-----------------------------------------------84
4.3.6 Choosing the Battery Type----------------------------------85
4.3.7New trends in applications---------------------------------86
4.3.8Management and control hierarchy of storage systems-89
4.3.8.1Internal configuration of battery storage systems---89
4.3.8.2External connection of EES systems----------------90
Chapter (5)
Transformer
5.1Introduction------------------------------------------------------96
5.2 What is a transformer? -----------------------------------------97
5.3 Types of transformers-------------------------------------------98
5.4Main Parts of Distribution Transformers----------------------98
5.4.1Iron Core----------------------------------------------------98
5.4.2Windings----------------------------------------------------99
5.4.3Tank---------------------------------------------------------99
5.4.4Oil Expansion Conservator-------------------------------99
5.4.5Terminals---------------------------------------------------99
5.4.6TapChanger------------------------------------------------99 IV
5.4.7Cooling Oil--------------------------------------------------99
5.5Number of phases-----------------------------------------------100

Content
5.6Transformerratios----------------------------------------------100
5.7The regulation of a transformer-----------------------------100
5.8The efficiency of a transformer-----------------------------101
5.9Parallel operation of the transformers----------------------101
5.10Methods of cooling-------------------------------------------102
5.10.1Oil-Immersed Distribution Transformer------------102
5.1.0.2Dry-type transformer--------------------------------103
5.11 Specification of the used transformer-------------------103
5.12Determining capacity of thetransformer-----------------104
Chapter (6)
Cables
6.1 Introduction --------------------------------------------------------107
6.2 Factors considered in design and selection of cables ---------107
6.3 Cable insulation materials ---------------------------------------108
6.3.1 Paper -----------------------------------------------------------108
6.3.2 P.V.C. ---------------------------------------------------------108
6.3.3 Thermosetting (XLPE) --------------------------------------108
6.4 Derating Factors ---------------------------------------------------108
6.5 Calculation of cross section of cables --------------------------110
6.5.1Cables selected in our project -------------------------------111
6.5.1.1 Medium voltage cable ------------------------------------111
6.5.1.2 Low voltage cable -----------------------------------------112
6.6 voltage drop calculation ------------------------------------------114
6.6 Joints and terminations ----------------------------------------117
6.7 Cable trays ---------------------------------------------------------118
6.7.1 Types of cable trays-----------------------------------------118
6.7.1.1 Ladder ------------------------------------------------------118
4.7.1.2 Cable Tray (Race Ways) ---------------------------------118
6.8 The Conduits ------------------------------------------------------119
6.9 Cable Trench / Channel ------------------------------------------120
6.10 Distribution panels ----------------------------------------------122
6.10.1 Medium voltage distribution panel (M.V.D.P) --------123
6.10.1.1 Measuring instruments ----------------------------------123
6.10.1.2 Protection instruments -----------------------------------124
6.10.1.3 switchgears instruments ---------------------------------124
6.10.2 Low voltage distribution panel ---------------------------125
6.10.2.1 Main panel ------------------------------------------------125
6.10.2.2 Sub panels -------------------------------------------------126 V

Content
Chapter (7)
Earthing
7.1 Introduction --------------------------------------------------------128
7.2 The advantages of earthing --------------------------------------128
7.3 The disadvantages of earthing -----------------------------------129
7.3.1 The two important disadvantages are ---------------------129
7.4Combining neutral with earth ------------------------------------130
7.5 In household wiring -----------------------------------------------130
7.6 IEC Terminology--------------------------------------------------131
7.6.1 TN network ---------------------------------------------------131
7.6.2 TT network ---------------------------------------------------133
7.6.3 IT network ----------------------------------------------------134
7.7 Theory vs. Practice------------------------------------------------134
7.8 Earth Electrode Measurement (Single Electrode) ------------135
7.9 Earth Electrode Measurement (Multiple Probe System) -----137
7.10 Soil Resistivity ---------------------------------------------------139
Chapter (5)
Protection system
8.1 Introduction --------------------------------------------------------144
8.2 Circuit breaker -----------------------------------------------------145
8.3 The types of the Circuit breakers -------------------------------145
8.3.1 Medium voltage circuit breaker ----------------------------145
8.3.2 Low voltage circuit breakers -------------------------------146
8.3.2.1 Miniature circuit breaker---------------------------------146
8.3.2.2 Molded case circuit breaker ------------------------------148
8.4 Types of protection used in our project ------------------------148
8.4.1 Over-current protection -------------------------------------148
8.4.2 Earth-fault protection ---------------------------------------150
8.4.3 Short circuit protection -------------------------------------150
8.5 Calculation of short circuit current -----------------------------151
8.5.1 Steps of impedance calculations used in short circuit -151
current calculations------------------------------------------------153
8.5.2 calculation of short circuit current for block (1)---------153
8.5.3 Calculation of short circuit current for other blocks ----154
VI

Introduction
Chapter 1
IN THIS CHAPTER:
 The scope of the project
 objectives of the project

Introduction Chapter1
1.1Introduction
Over the recent years most of the Middle East countries were still
building their infra-structure like industrial, commercial and civil
projects. However whether the project is industrial or civil, it can’t
be done without scientific electricity distribution systems, so the
distribution system has the biggest importance in the construction
of any project. So sophisticated standards were set and improved to
assure that all designs and installations are made in highest quality
to achieve the desired safety for employee and public with highest
performance and less cost.
So we got the best approach to achieve these goals by illustrating

every equipment and system used in this project using some charts
and figures and finally we presented our vision in selections
according to several factors will be mentioned .So we spent our best
efforts to display our point of view in this project in clearest way
and we insist also to be unique by covering several topics.
1.2 The scope of the project:

In this project we have designed a distribution system on a tourist
resort closed to the sea with a total area of 58400 m² named
SMART CITY that still under construction. It consists of:
1. Many residential buildings of different floors.

2. Commercial buildings such as mall center, shops and office.
3. Hotel.
4. Entertainment places such as Swimming pool ,tennis club and
restaurant
Type of loads contained by the building is very variety as it

contains lighting loads, power loads and emergency loads that must
provided by permanent source of electrical power using standby
generator unit connected through A.T.S (Automatic transfer
switch).
Protection system will be provided to all the electrical system using
circuit breakers and sensitive relay.
2

1.3 objectives of the project:
There are many objectives that must be achieved and

satisfied through design which are:
1. Studying the different load types.

2. Studying the medium and low voltage and the connection between
them.
3. Determining the different types of protection.
4. Determining the required measurement devices.
5. Studying the earthing of the resort.
So in our project we will study the load to obtain the total power
absorbed by the load and relevant position and the position of the
power distribution centers (switchboards); after that we can
calculate the length of the connection elements.
According to the result of the total power absorbed by the load we

can determine the dimension of the transformers and generators.
After knowing the total power absorbed and the dimensions of the
transformer we can calculate the dimensions of the conductors by
evaluation of the current (Iload) in the single connection elements;
and we must know the conductors type (conductors and insulation
materials, configuration, ……); by knowing the length and the
cross section of the conductors we can calculate the voltage drop at
the load current under specific reference conditions and compare it
with the voltage drop limits at the final loads to modification the
dimensions of the conductors.
Now we must protect this equipment by calculating the short-circuit

current at maximum values at the bus bar (beginning of line) and
minimum values at the end of line to select the protective circuit-
breakers according to breaking capacity which must be higher than
the maximum prospective short-circuit current and it's rated current
In not lower than load current Iload; with taking into the characteristic
compatible with the type of protected load (motors, capacitors,
…..).
After that the grounding or earthing is done for safety purposes to
protect people from the effects of faulty insulation on electrically 3
powered equipment. A connection to ground helps limit the voltage
built up between power circuits and the earth, protecting circuit
insulation from damage due to excessive voltage.
Fig 1-1 shows the flow chart summering the steps of this project.
Load analysis:
- Definition of the power absorbed by the load and
relevant position;
- Definition of the position of the power distribution
centers(switchboards)
- Definition of the paths and calculation of the length of
the connection elements
- Definition of the total power absorbed, taking into
account the utilization factor and demand factors
Dimensioning of transformers and generators with

margin connected to future predicable power supplay
requirements (by approxmation from +15/30%)
Dimensioning of conductor:
- evaluation of the current (Ib) in the single connection
elements,
- definition of the conductor type (conductors and
isolation materials,
Configuration,...)
- definition of the cross section and of the current
carrying capacity,
- calculations of the voltage drop at the load current
under specific refrance
Conditions (motor starting,...).
Verification of the voltage drop limits at the final

loads
Short-circuit current calculation maximum values at

the busbar (begining of Line) and minimum values the 4
end of line

Selection of protective circuit-breakers with:

-breaking capacity higher than the maximum prospective
short-circuit current ,
-rated current In not lower than the load Ib
-characteristics compatible with the type of protected
load (motors, capacitors...)
Fig 1-1 main steps of the project.
By adding new renewable resources such as wind and photovoltaic

power generation to the studying project, more advantages could be
gained. These are
 It is renewable; therefore it is sustainable and so will never run out.
 Renewable energy facilities generally require less maintenance than
traditional generators.
 Their fuel being derived from natural and available resources
reduces the costs of operation.
 Renewable energy produces little or no waste products such as
carbon dioxide or other chemical pollutants, so has minimal impact
on the environment.
 Renewable energy projects can also bring economic benefits to
many regional areas, as most projects are located away from large
urban centers and suburbs of the capital cities. These economic.
Benefits may be from the increased use of local services as well as
tourism.
In order to improve the reliability of the power supply, we use the
Energy storage system.

Primary &
Secondary Service
and System
Configuration
Chapter 2
IN THIS CHAPTER:
 Types of Sub transmission lines
 Type of Substation bus scheme
 Comparison of Configurations
Primary and Secondary Service and System Configurations Chapter2
2.1 Introduction
In order to provide electrical service to a building or buildings,
you must first determine what type of system is available from the
utility company or from a privately owned and operated system
such as might be found on a college or university campus or
industrial or commercial complex, as the case may be. Once this
is known, it is important to understand the characteristics of the
system—not only voltage, capacity, and available fault current but
also the operational, reliability, and relative cost characteristics
inherent to the system by virtue of its configuration or arrangement.
Knowing the characteristics associated with the system arrangement,
the most appropriate service and distribution system for the
application at hand can be determined.
2.2 Types of Sub transmission lines

1. Radial Circuit Arrangements in Commercial
Buildings
2. Radial Circuit Arrangement Common Primary Feeder to
Secondary Unit Substations
3. Radial Circuit Arrangement: Individual Primary Feeder to
Secondary
4. Unit Substations
5. Primary Radial-Selective Circuit
Arrangements
6. Secondary Selective Circuit Arrangement (Double-Ended
Substation with
7. Single Tie)
8. Secondary-Selective Circuit Arrangement (Individual
Substations with
9. Interconnecting Ties)
10. Primary and Secondary-Selective Circuit Arrangement
(Double-Ended)
11. Substation with Selective Primary
12. Looped Primary Circuit Arrangement
13. Basic Spot Network

2.2.1 Radial circuit arrangements in commercial buildings
Fig (3.1) Radial circuit arrangements.
2.2.1.1 Characteristics
1. Simplest and lowest cost way of distributions.
2. Lowest reliability. A fault in the supply circuit, transformer, or the
main bus will cause interruption of service to all loads.
3. Modern distribution equipment has demonstrated sufficient
reliability to justify use of the redial circuit arrangement in many
applications.
4. Most commonly used circuit arrangement

2.2.2Radial circuit arrangement:Common primary feeder

to Secondary unit substations
Fig (2.2) Common primary feeder to secondary unit substations.
2.2.2.1Characteristics
 Multiple small rather than single large secondary substations.
 Used when demand, size of building, or both may be required to
maintain adequate voltage at the utilization equipment.
 Smaller substation located close to center of load area.
 Provides better voltage conditions, lower system losses, less
expensive installation cost than using relatively long, high-
amperage, low-voltage feeder circuits.
 A primary feeder fault will cause the main protective device to
operate and interrupt service to all loads. Service cannot be restored
until the source of trouble has been eliminated.
 If a fault were in a transformer, service could be restored to all
loads except those served by that transformer.

2.2.3 Radial circuit arrangement: Individual primary

feeder to Secondary unit substations
Fig (2.3) Individual primary feeder to secondary unit substations
 First three characteristics are the same as figure 3.2
 This arrangement has the advantage of limiting outages, due to a
feeder or transformer, to the loads associated with the faulted
equipment
 The cost is usually higher than the arrangement shown in figure
2.2
10

2.2.4 Primary radial-selective circuit arrangements
(a) fused Dual switches (b) Duplex load interrupter switches with
transformer primary fuses
Fig (2.4) Primary radial-selective circuit arrangements
 These circuit arrangements reduce both the extent and duration of
an outage caused by a primary feeder fault.
 Operating feature - duplicate primary feeder circuit and load
interrupter switches, permit connection to either primary feeder
circuit.
 Each feeder must be capable of saving the entire load.
 Suitablesafety interlocks usually required to prevent closing of
both switches at the same time.
 Under normal operating conditions, appropriate switches are
closed to balance loads between two primary feeder circuit.
 Primary-selective switches are usually manually operated, but can
be automated for quicker restoration of service. Automated switching
is more costly but may be justified in many applications.
11
 If a fault occurs in a secondary substation transformer, service can
be restored to all loads except those served from the faulted
transformer.

 The higher degree of service continuity afforded by the primary-

selective arrangement is realized at a cost that is usually 10%-20%
higher than the circuit arrangement of figure 2.4.
2.2.5 Secondary-selective circuit arrangement (Double-

ended substation with single tie)
Fig (2.5) Double-ended substation with single tie
 Under normal conditions, operates as two separate radial systems
with the secondary bus-tie circuit breaker normally open.
 Loads should be divided equally between the two bus sections.
 If a fault occurs on a primary feeder or in a transformer, service is
interrupted to all loads served from that half of the double-ended
arrangement. Service can
be restored to all secondary buses by opening the secondary main
on the faulted side and closing the tie breaker.
 The main-tie-main breakers are normally interlocked to prevent
paralleling the transformer and to prevent closing into a secondary
bus fault. They can also be automated to transfer to standby operation
and retransfer to normal operation.
 Cost of this arrangement will depend upon the spare capacity in
the transformer and primary feeder. The minimum will be determined
by the essential loads that need to be served under standby operating
conditions. If service is to be provided for all loads under standby
conditions, then the primary feeders and transformers must be 12
capable of carrying the total load on both substation buses.

 This circuit arrangement is more expensive than either the radial or

primary selective circuit configuration. This is primarily due to the
redundant transformers.
2.2.6 Secondary-selective circuit arrangement (Individual

substations with interconnecting ties)
Fig (2.6) Individual substations with interconnecting tie
 In this modification of the secondary-selective circuit
arrangement shown if figure, there is only one transformer in each
secondary substation; but adjacent substations are interconnected in
pairs by a normally open low-voltage tie circuit.
 When the primary feeder or transformer supplying one secondary
substation bus is out of service, essential loads on that substation bus
can be supplied over the tie circuit.
 Operating aspects of this system are somewhat complicated if the
two substations are separated by distance.
 This would not be a desirable choice in a new building service
design because a multiple key interlock system would be required to
avoid tying the two substations together while they were both
energized.
13

2.2.7 Primary- and secondary-selective circuit arrangement

(Double-ended substation with selective primary)
Fig (2.7) Double-ended substation with selective primary
 Used when highly reliable service is needed, such as hospital or
data center loads.
 Has the combined benefits and characteristics of the arrangement
shown in figure and figure
 Small premium cost over configuration shown in figure
forprimary selector switches.
14

2.2.8 Looped primary circuit arrangement
(a) Closed loop (obsolete) (b) Open loop

Fig (2.8) Looped primary circuit arrangement
 Basically a two-circuit radial system with the ends connected
together forming a continuous loop.
Early versions of the closed loop in (a) above, although relatively

inexpensive, fell into disfavor because of its apparent reliability
advantages are offset by interruption of all service from a fault
occurring anywhere in the loop, by the difficulty of locating
primary faults, and by safety problems associated with the no load
break, or "dead break", isolating switches.
 Newer open-loop version as shown in (b) above, designed for
modern underground commercial and residential distribution
systems, utilize fully rated air, oil, vacuum, and SF6 interrupter
switches. Equipment available up to 34.5 kilovolt with interrupting
rating for both continuous load and fault currents to meet most
system requirements. certain equipment can closed and latch on
fault current, equal to the equipment interrupting values, and still be
operational without maintenance. 15
 Major advantages of the open-loop primary systems over the
simple radial system is the isolation of cable or transformer faults or
both, while maintaining continuity of service to the remaining

loads. With coordinated transformer fusing provided in the loop-tap

position, transformer faults can be isolated without any interruption
of primary service. Primary cable faults will temporarily drop
service to half of the connected loads until the fault is located; the,
by selective switching the unfaulted sections can be restored to
service, leaving only the faulted section to be repaired.
 Disadvantages; increased costs to fully size cables, protective
devices and interrupters to total capacity of the load, and the time
delay necessary to locate the fault, isolate the section, and restore
service. Safety considerations in maintaining a loop system are
more complex than for a radial or a primary-selective system.
2.2.9 Basic spot network
Fig (2.9) Basic spot network
 The spot network is a localized distribution center consisting of
two or more transformer/network protector units connected to a
common bus called a "collector bus". A building may have one or
more spot network services.
 Spot network are employed to provide a reliable source of power 16
to important electrical loads. Spare capacity is built in to allow for
at least one contingency, i.e., loss of a transformer or primary
network feeder will cause no interruption of service.

 Planning for service continuity should be extended beyond the

consideration of using a utility primary feeder or transformer. The
consequences of severe
equipment damage including the resulting system downtime should

also be considered.
 The primary side of a spot network transformer usually contains
an isolating/load interrupter switch, primary side fuses, and anon-
load break grounding switch located within the same enclosure.
Although the grounding switch has a fault closing rating, it cannot
be operated until the safety requirement of a key interlock scheme
has been satisfied. The key interlocks
prevent closing the grounding switch until all possible sources of
supply to the feeder have been isolated.
 Conventional automatic network protectors are sophisticated
devices. They are self-contained units consisting of an electrically
operated circuit breaker, special network relays, control
transformers, instrument transformer, and open-type fuse links. the
protector will automatically closed when the oncoming transformer
voltage is greater than the collector bus voltage and will open when
reverse current flows can be result of a fault beyond the line side of
the protector, supplying load current back into the primary
distribution system when the collector bus voltage is higher than the
individual transformer voltage, or the opening of the transformer
primary feeder breaker, which causes the collector bus to supply
transformer magnetizing current via the transformer secondary
winding.
 Most spot network applications for commercial building provide
480Y/277-volt utilization, thus requiring ground fault protection.
Relay protection is the most common method of ground-fault
protection. The fault current may be sensed by the ground return,
residual, or zero-sequence method. Each of the methods have
proved successful where appropriately applied; but they share a
common limitation in that they cannot distinguish between in-zone
and thru-zone ground faults unless incorporated in a complex
protection scheme.One particular method of ground-fault detection
that is not prone to unnecessary tripping is enclosure monitoring.
This method offers the distinct advantage of not requiring
coordination with other protective devices.
17

2.3 Type of Substation bus scheme

Type of substation bus scheme
Various factors affect the reliability of a substation or switchyard,
one of which is the arrangement of the buses and switching devices.
In addition to reliability, arrangement of the buses/switching
devices will impact maintenance, protection, initial substation
development, and cost. There are six types of substation
bus/switching arrangements commonly used in air insulated
substations:
1. Single bus.
2. Double bus, double breaker.
3. Main and transfer (inspection) bus.
4. Double bus, single breaker.
5. Ring bus.
6. Breaker and a half.
3.3.1 Single Bus scheme

This arrangement involves one main bus with all circuits connected
directly to the bus. The reliability of this type of an arrangement is
very low. When properly protected by relaying, a single failure to
the main bus or any circuit section between its circuit breaker and
the main bus will cause an outage of the entire system. In addition,
maintenance of devices on this system requires the de-energizing of
the line connected to the device. Maintenance of the bus would
require the outage of the total system, use of standby generation, or
switching to adjacent station, if available.
Since the single bus arrangement is low in reliability, it is not
recommended for heavily loaded substations or substations having a
high availability requirement. Reliability of this arrangement can be
improved by the addition of a bus tiebreaker to minimize the effect
of a main bus failure.
Advantages
1. Lowest cost.
2. Small land area required.
3. Easily expandable. 18
4. Simple in concept and operation.
5. Relatively simple for the application of protective relaying.

Disadvantages
1. High-profile arrangement equipped with circuit breaker bypass
facilities does not provide for circuit protection when bypass
facilities are being used inside the substation.
2. A single bus arrangement has the lowest reliability.
3. Failure of a circuit breaker or a bus fault causes loss of the entire
substation.
4. Maintenance switching can complicate and disable some of the
protective relay scheme and over all relay coordination.
5. Maintenance at the upper elevations of high-profile arrangements
necessitates de-energization or protection of the lower equipment.
Fig(2.10) Single bus.
2.3.2 Double Bus, Double Breaker scheme

This scheme provides a very high level of reliability by having two
separate breakers available to each circuit. In addition, with two
separate buses, failure of a single bus will not impact either line.
Maintenance of a bus or a circuit breaker in this arrangement can be
accomplished without interrupting either of the circuits.
This arrangement allows various operating options as additional
lines are added to the arrangement; loading on the system can be
shifted by connecting lines to only one bus.
A double bus, double breaker scheme is a high-cost arrangement,
since each line has two breakers and requires a larger area for the 19
substation to accommodate the additional equipment. This is
especially true in a low profile configuration. The protection
scheme is also more involved than a single bus scheme.

Fig (2.11) Double bus, double breaker.
2.3.3 Main and Transfer Bus scheme

This scheme is arranged with all circuits connected between a main
(operating) bus and a transfer bus (also referred to as an inspection
bus). Some arrangements include a bus tie breaker that is connected
between both buses with no circuits connected to it. Since all circuits
are connected to the single, main bus, reliability of this system is not
very high. However, with the transfer bus available during mainte-
nance, de-energizing of the circuit can be avoided. Some systems are
operated with the transfer bus normally de-energized. When
maintenance work is necessary, the transfer bus is energized by either
closing the tie breaker, or when a tie breaker is not installed, closing
the switches connected to the transfer bus. With these switches
closed, the breaker to be maintained can be opened along with its
isolation switches. Then the breaker is taken out of service. The
circuit breaker remaining in service will now be connected to both
circuits through the transfer bus. This way, both circuits remain
energized during maintenance. Since each circuit may have a
different circuit configuration, special relay settings may be used
when operating in this abnormal arrangement. When a bus tie breaker
is present, the bus tie breaker is the breaker used to replace the
breaker being maintained, and the other breaker is not connected to
the transfer bus.
A shortcoming of this scheme is that if the main bus is taken out of
service, even though the circuits can remain energized through the 20
transfer bus and its associated switches, there would be no relay
protection for the circuits. Depending on the system arrangement, this

concern can be minimized through the use of circuit protection

devices (reclosure or fuses) on the lines outside the substation.
This arrangement is slightly more expensive than the single bus
arrangement, but does provide more flexibility during maintenance.
Protection of this scheme is similar to that of the single bus
arrangement. The area required for a low profile substation with a
main and transfer bus
scheme is also greater than that of the single bus, due to the
additional switches and bus.
Advantages
1. Accommodation of circuit breaker maintenance while maintaining
service and line protection.
2. Accommodation of circuit breaker maintenance while maintaining
service and line protection.
3. Reasonable in cost.
4. Fairly small land area.
5. Easily expandable.
Disadvantages
1. An additional circuit breaker is required for bus tie.
2. Since the bus tie breaker, have to be able to be substituted for any
line breaker, its associated relaying may be somewhat complicated.
3. Failure of a circuit breaker or a bus fault causes loss of the entire
substation.
4. Somewhat complicated switching is required to remove a circuit
breaker from service for maintenance.
21

Fig (2.12) Main and transfer bus.
2.3.4 Double Bus, Single Breaker scheme

This scheme has two main buses connected to each line circuit
breaker and a bus tie breaker. Utilizing the bus tie breaker in the
closed position allows the transfer of line circuits from bus to bus by
means of the switches. This arrangement allows the operation of the
circuits from either bus. In this arrangement, a failure on one bus will
not affect the other bus. However, a bus tie breaker failure will cause
the outage of the entire system.
Operating the bus tie breaker in the normally open position defeats
the advantages of the two main buses. It arranges the system into two
single bus systems, which as described previously, has very low
reliability.
Relay protection for this scheme can be complex, depending on the
system requirements, flexibility, and needs. With two buses and a
bus tie available, there is some ease in doing maintenance, but
maintenance on Line breakers and switches would still require
outside the substation switching avoiding outages. 22

Fig(2.13) Double bus, single breaker.
2.3.5 Ring Bus scheme

In this scheme, as indicated by the name, all breakers are arranged in
a ring with circuits tapped between breakers. For a failure on a
circuit, the two adjacent breakers will trip without affecting the rest
of the system. Similarly, a single bus failure will only affect the
adjacent breakers and allow the rest of the system to remain
energized. However, a breaker failure or breakers that fail to trip will
require adjacent breakers to be tripped to isolate the fault.
Maintenance on a circuit breaker in this scheme can be accomplished
without interrupting any circuit, including the two circuits adjacent to
the breaker being maintained. The breaker to be maintained is taken
out of service by tripping the breaker, then opening its isolation
switches. Since the other breakers adjacent to the breaker being
maintained are in service, they will continue to supply the circuits.
In order to gain the highest reliability with a ring bus scheme, load
and source circuits should be alternated when connecting to the
scheme. Arranging the scheme in this manner will minimize the
potential for the loss of the supply to the ring bus due to a breaker 23
failure.

Relaying is more complex in this scheme than some previously

identified. Since there is only one bus in this scheme, the area
required to develop this scheme is less than some of the previously
discussed schemes. However, expansion of a ring bus is limited, due
to the practical arrangement of circuits.
Advantages
1. Flexible operation.
2. High reliability.
3. Isolation of bus sections and circuit breakers for maintenance
without disrupting circuitoperation .
4. Double feed to each circuit.
5. No main buses.
6. Expandable to breaker-and-a-half configuration .
7. Economic design.
Disadvantages
1. Ring may be split by faults on two circuits or a fault during
breaker maintenance to leave possibly undesirable circuit
combinations (supply/load) on the remaining bus sections. Some
consider this, however, to be a second contingency factor.
2. Each circuit has to have its own potential source for relaying.
This configuration is usually limited to four circuit positions,

although larger rings are in service, including 10-position ring buses.
A 6-position ring bus is usually considered as a maximum limit for
the number of terminals in a ring bus.
24
Fig (2.14) Ring bus

2.3.6 Breaker-and-a-Half scheme

The breaker-and-a-half scheme can be developed from a ring bus
arrangement as the number of circuits increases. In this scheme, each
circuit is between two circuit breakers, and there are two main buses.
The failure of a circuit will trip the two adjacent breakers and not
interrupt any other circuit. With the three breaker arrangement for
each bay, a center breaker failure will cause the loss of the two
adjacent circuits. However, a breaker failure of the breaker adjacent
to the bus will only interrupt one circuit.
Maintenance of a breaker on this scheme can be performed without
an outage to any circuit. Further- more, either bus can be taken out of
service with no interruption to the service.
This is one of the most reliable arrangements, and it can continue to
be expanded as required. Relaying is more involved than some
schemes previously discussed. This scheme will require more area
and is costly due to the additional components.
Advantages
1. Flexible operation
2. High reliability.
3. Can isolate either main bus for maintenance without disrupting
service.
4. Can isolate any circuit breaker for maintenance without disrupting
service.
5. Double feed to each circuit6.Bus fault does not interrupt service to
any circuits.
6. All switching done with circuit breakers.
Disadvantages
1. One-and-a-half breakers are required per circuit.
2. Relaying is involved, since the center breaker has to respond to
faults of either of its associated circuits.
3. Each circuit should have its own potential source for relaying.
25

Fig(2.15) Breaker-and-a-half.
2.4 Comparison of Configurations

In planning an electrical substation or switchyard facility, one should
consider major parameters as discussed above: reliability, cost, and
available area. Table (3.1) has been developed to provide specific
items for consideration.
In order to provide a complete evaluation of the configurations
described, other circuit-related factors should also be considered. The
arrangement of circuits entering the facility should be incorporated in
the total scheme. This is especially true with the ring bus and
breaker-and-a-half schemes, since reliability in these schemes can be
improved by not locating source circuits or load circuits adjacent to
each other. Arrangement of the incoming circuits can add greatly to
the cost and area required.
Also, the profile of the facility can add significant cost and area to the
overall project. A high-profile facility can incorporate multiple
components on fewer structures. Each component in a low-profile
layout requires a single area, thus necessitating more area for an
arrangement similar to a high-profile facility. Therefore, a four-
circuit, high-profile ring bus may require less area and be less 26
expensive than a four-circuit, low-profile main and transfer bus
arrangement.

Configuration Reliability Cost Available Area

Single bus Least reliable — Least cost (1.0) Least area —
single failure — fewer fewer
can cause components components
complete outage
Double bus Highly reliable High cost Greater area —
— duplicated twice as many
—
components; components
single failure duplicated
normally components
isolates single
Main bus and Least reliable — Moderate cost Low area
transfer same as Single requirement —
—
bus, but
fewer
flexibility in fewer
components
operating and components
maintenance
Double bus, Moderately Moderate cost Moderate area
single breaker reliable — — more
—
depends on components
arrangement of more
components and components
bus
Ring bus High reliability Moderate cost Moderate area

— single failure — increases
—
isolates single with number of
component more circuits
components 27

Breaker-and-a- Highly reliable Moderate cost Greater area

half —
— —
single circuit
breaker-and-a- more
failure isolates
half for each components per
single circuit,
circuit circuit
bus failures do
not affect
circuits
Table(2.1) Comparison of Configurations
28

Load Estimation
IN THIS CHAPTER:
Chapter 3
 Description of the project land
 considerations of load calculations
 Load calculations of buildings
 Load calculation of blocks
 Critical loads
Load Estimation Chapter3
3.1 Introduction
Load calculation is as important as it helps in cable cross section
design, circuit breaker design, transformer rating and distribution
boards.
3.2 Description of the project land

In this project we have designed a distribution system on a tourist
resort closed to the sea with a total area of 58400 m² named SMART
CITY that still under construction. It consists of many buildings of
different loads such as residential flats, mall, hotels, offices, etc. In
order to find the suitable rating of the distributed transformers, the
area of the SMART CITY has been divided into seven blocks these
are:
Block (1)
 The total area of this block is 6900m² and consists of:
a- Building (named 10C) of area 795m².
b- Building (5) of area 820m².
c- Buildings (13A) of area 680m².
d- Building (13B) of area 910m².
 The ground of this block consists of:
a- Shops of area 900m².
b- Stores of area 2300m².
Block (2)
A- Mall region
* Mall which is consists of two floors of area 350m².
* Swimming pool of area 220m².
* Tennis playground of area 1060m².
* Water fountain of area 50m².
* Restaurant of area 1750m².
B- A Hotel which is consists of:
* Two buildings of 13 floors of area 590m² for each. 29
* A building of 3 floor of area 40m².
* A building of 2 floors of area 80m².
* Two buildings of 6 floors of area 540m² for each.

C- An Office which is consists of:

* Building of 10 floors of area 910m².
* Two buildings of 6 floors of area 445m² for each.
Block (3)
a- Building (10C) of area 795m².
c- Buildings (13A) of area 680m².
d- Building (13B) of area 910m².
b- Lobbies of area 528m².
c- Bath rooms of area 66m².
d- Gymnasium rooms of area 264m².
Block (4)
 The total area of this block is 9200m² and consist of two same
parts, each part consist of:
a- Buildings (13A) of area 680m².
c- Building (13B) of area 910m².
 The ground of each part consists of:
c- Bath rooms of area 66m²
d- Gymnasium rooms of area 264m²
Block (5)
 The total area of this block is 5100m² and consists of building of
10, 8, 6, 5 and 4 floors.
a- Prayer rooms of area 200m².
c- Shops of area 1585m². 30
d- Gymnasium rooms of area 200m².

Block (6)
 Is the same as block (3) in its construction and area.
Block (7)
 Is the same as block (1) in its construction, but its area is 7300m².
 The ground of this block is stores of area 3205m².
Note:
• The ground of each block is connected under buildings.
3.3 considerations of load calculations:

Tables (3-1) and (3-2) investigates the points taken into
considerations while calculating the building Loads in this project
according to [1]. Where Table (2-1) shows the lightning and air
condition loads and table (3-2) shows the power load.
Table (3.1) the lightning and air condition loads consideration
Type Lighting Air condition

(KVA /100 m2) (KVA/100m2)
Hotel 3 4
Ground 4
Office 3 5
Ground 3
Shops 5 7
Mall 4 8
Flat unit 3 7
Table (3.2) the power load consideration
Load type KVA
Fire pump 14
Water pump 9.4
Elevators motor 18.75 31
Elevators motor of mall 9.4

Escalators 9.4
In addition, these points are taken into considerations

 Basement 2 KVA /100m².
 Swimming pool :
-Lighting 2 KVA/100 m²
-Pump 15 hp
 water fountain
-Lighting 2 KVA/100 m²
-Pump 5 hp
 Tennis playground 4 KVA/100 m²
 Street lighting 2 KVA/100 m²
3-3-1 Diversity factor:

Diversity factor is important factor used in calculating loads; it is
the ratio of the sum of the individual maximum demands of the
various subdivisions of a system, or part of that system, to the
maximum demand of the whole system, or part of that system. Table
(3-3) shows the values of the diversity factors used in this project.
Table (3.3) the values of the diversity factors used in this project
Type Diversity factor

Flat 0.6
Residential building 0.8
Hotel 0.4
Office 1
Mall 1
Note: 32
• In this project, 0.8 power factor is used.

3.4 Load calculations of buildings.

The load calculation of the building depends on its area and the
previous consideration
3.4.1 Building (13A):
 The Area of the building is 680 m2 and it consists of 13 floors.
 Each floor consists of 4 flats. The area of each is 160 m2
3.4.1.1 Calculation of flat load:

The load of the flat =area* standard lighting and air condition
=160* (3+7)/100 =16 KVA
by using the diversity factor, the load becomes
Load of flat =load of flat * flat diversity factor
=16 * 0.6 =9.6 KVA
Load of flat per phase =9.6/3=3.2 KVA
3-4-1-2 Calculations of the total building loads:
a- The Load of the building per phase =

Load of flat per phase * no. of flat per floor * no. of floors
= 3.2 * 4 * 13 = 166.4 KVA
By using the diversity factor, the load becomes
Load of building =load of building* building diversity factor
=166.4 * 0.8 =133.12 KVA
b- Load of building service =area * standard of building service
=680 * 2/100 =13.6 KVA
Load of building service per phase =13.6/3 =4.5 KVA
c- We take three water pump one of them is spare
Load of water pump =no. of pumps* KVA of pump
=2* 9.4 =18.75 KVA
d- Load of fire pump =no. of pumps* KVA of pump
=2 * 14 =28 KVA
e- Elevators =no of elevators* KVA of motor
=2*18.75 =37.5 KVA
f- Load of basement =area* standard of basement
33
=680 * 2/100 =13.6 KVA
Load of basement per phase =13.6/3=4.5 KVA

g- Total load of building per phase =679.11/3

=226.37 KVA
Table (3.4) the load of building (13A) per phase.
Load KVA
Building load 133.12
Service of Building 4.5
Basement 4.5
Water pumps 18.75
Fire pumps 28
Elevators 37.5
Total load 226.37
3-4-2 Building (13B):
 The building consists of 13 floors. Each floor consists of 4 flats.

The area of each is 160 m2.
 This building is connected to another building of 4 floors; each
floor consists of 4 flats. The area of each is 55 m2. The total load of
this building is calculated as follow.
Load of flat =area* standard lighting and air condition
= 55*(3+7)/100 = 5.5 KVA
Load of flat =Load of flat*diversity factor of flat
= 5.5*0.6 =3.3 KVA
Load of flat per phase =3.3/3=1.1 KVA
a- Load of building per phase = Load of flat per phase *no. of flats
per floor * no. of floors =1.1*4*4 =17.6 KVA
By using the diversity factor, the load becomes Load of building =
load of building per phase *diversity factor of building = 17.6*0.8
=14.08 KVA
b- Service of building =area *standard of service
= 230*2/100 = 4.6 KVA 34
 service of building per phase =4.6/3 =1.53 KVA

c- Basement of building =area* standard of basement

=230*2/100 = 4.6 KVA
 basement of building per phase =4.6/3 =1.53 KVA
d- Total load of building of 4 floors per phase =17.14 KVA

Then the Total load of building (13B) is calculated as follow
The total load of building (13B) per phase = Total load of building
(13A) per phase+ Total load of building of 4 floors per phase
=226.37+17.14 = 243.51 KVA
Table (3.5) the load of building (13B) per phase.
Load KVA
Building load 148
Basement 6.03
Water pumps 18.75
Fire pumps 28
Elevators 37.5
Total load 243.51
3.4.3 building (10C):

 The building consists of 10 floors. Each floor consists of 4 flats.
The area of each is 160 m2.
 This building is connected to another building of 4 floors; each
floor consists of 2 flats. The area of each is 55 m2.
- By using the same procedure used in sections (3-4-1) & (3-4-2),
the loads of building (10C) is calculated and are shown in table (3-
6).
Load KVA
Building load 109.4
Basement 6.03
Water pumps 18.75
Fire pumps 28
Elevators 37.5
Total load 205.7 35
Table (3.6) Loads of building (10C) per phase.

3.4.4 building (5):

- By using the same procedure used in sections (3-4-1) & (3-4-2),
the loads of building (5) is calculated and are shown in table (3-7).
Table (3.7) the load of building (5) per phase.
Load KVA
Building load 66
Basement 5.5
Total load 77
3.5 Load calculation of blocks:

The load calculation of the block depends on its area and the
previous consideration
3.5.1 Block (1):
a- Load of streets =area *standard of street’s light
=3695*2/10 =73.9 KVA
Load of streets per phase =73.9/3 =24.6 KVA
b- Load of ground
the ground in block (1) consists of shops and stores of area 900m2,
2300m2 respectively.
 Load of shops = area *standard of shops
= 900*12/100 = 108 KVA
Load of shops per phase=108/3 =63 KVA
 Load of stores= area *standard of stores
=2300*2/100=46 KVA
Load of stores per phase =46/3 =15.33 KVA
 Total load of ground per phase =153.9/3 =51.3 KVA
Table (3.8) Total load of block (1).
Load KVA
Streets load 24.6
Ground load 51.3
Building (13A) 226.37
Building (13B) 243.51
Building (10C) 205.7 36
Building (5) 77
Total load of block 828.48

3.5.2 Block (2):

a- Load of streets =area *standard of streets light
= 6450*2/100=129 KVA
Load of streets per phase =129/3 = 43 KVA
b- Load of mall region:
Load of mall =area *no. of floors *standard lighting
=350*2*4/100 =28 KVA
Load of mall per phase = 28/3 =9.4 KVA
Load of air condition (A.C) =area * standard A.C
=350*8/10 =28 KVA
Load of A.C per phase =28/3 =9.33 KVA
Load of fire pump =no. of pumps *KVA of pump
=2*14 =28 KVA
Load of elevators =no. of elevators *KVA of motor
= 2*9.4 =18.75 KVA
Load of swimming pool per phase =(Area*standard)+KVA of
pump =1/3(220*2/100) + (15*0.746/0.8) =15.5 KVA
Load of water fountain = (Area* standard of water
fountain) + (no. of pumps*KVA of pumps)
=1/3(50*2/100) + (2*5*0.746/0.8) =9.7 KVA
Load of restaurant =area* standard of restaurant
=1750*3/100 = 52.5 KVA
Load of restaurant per phase =52.5/3 =17.5 KVA
Load of tennis playground = Area* standard of tennis
playground = 1060*4/100 = 42.4 KVA
Load of tennis per phase =42.4/3 =14.12 KVA
Load of basement = area* standard of basement
=9525* 2/100 =190.5 KVA
Load of basement per phase =190.5/3 =36.5 KVA
Total load of mall region =213.5 KV
c- Loads of Hotel: 37
Hotel consists of 2 building of 13 floors, building of 3 floors,
building of 2 floors and 2 building of 6 floors of area 590, 40, 80
and 540 m2 respectively.

Load of building =area* no. of floors* standard lighting

Load of building 6 floors = 540* 6* 3/100 = 97.2 KV
Load of building 13 floors =590* 13* 3/100 =230.1 KVA
Load of building 2 floors =80* 2* 3/100 =4.8 KVA
Load of building 3 floors=40* 3* 3/100 =3.6 KVA
Load of ground = area* standard of ground
=2380* 4/100=95.2 KVA
Total load =431 KVA
Total load of hotel =total load* diversity factor
=431* 0.4 =172.36 KVA
Total load per phase =172.36/3 =57.5 KVA
Load of water pump = no. of pumps* KVA of pump
=2* 9.4 =18.8 KVA
Load of fire pump =no. of pumps* KVA of pump
=4* 14=56 KVA
Load of elevators = No. of elevators* standard of motor of
elevators=4* 18.75 = 75 KVA
Load of A.C = total area of floors* standard of A.C
= [2380+ (13* 2* 590) + (40* 3) + (2* 80) + (1080*
6)]*4/100] =979.2 KVA
Load of A.C per phase =979.2 /3=326.4 KVA
Total load of Hotel per phase =546.7 KVA
d- Loads of office
The office consists of building of 10 floors and other
building of 6 floors of area 910, 890 m2 respectively.
Load of office =area* no. of floors* standard of office
Load of 10 floors =910* 10* 3/100=273 KVA
Load of 6 floors =890* 6* 3/100 =160.2 KVA
Load of ground =area* standard of ground
=1800* 3/100 =54 KVA
Total load =487.2 KVA
Total load of office =total load* diversity factor
=487.2* 1=487.2 KVA
Load of office per phase =487.2/3 =162.4 KVA
Load of A.C =total area of floors* standard of A.C 38
=14440* 5/100 =722KVA
Load of A.C per phase =722/3 =240.6 KVA

Load of water pump =no. of pumps* KVA of pump

=1* 9.5 =9.5 KVA
Load of fire pump =no. of pumps* KVA of pump
=2* 14 =28 KVA
Load of elevators =no. of elevators* standard of elevator
=2*18.75 =37.5 KVA
Total load of office per phase =478 KVA
Table (3.9) Total load of block (2).
load KVA
Streets load 43
Mall load 213.5
Hotel load 546.7
Office load 478
3.5.3 Block (3)

- By using the same procedure used in block (1) and (2), the loads
of block (3) is calculated and are shown in table (3-10)
Table (3.10) the total load of block (3)
Load KVA
Streets load 21.3
Ground load 87.8
Building (10C) 205.7
Building (5) 77
3.5.4 Block (4)

of block (4) is calculated and are shown in table (3-11).
39

Load KVA
Streets load 29.2
Ground load 138.6
Building (13A)1 226.37
Building (13A)2 226.37
Building (13B)1 243.51
Building (13B)2 243.51
Building (5)1 77
Building (5)2 77
3.5.5 Block (5)

Load KVA
Streets load 19.3
Ground load 68.72
The building 422.5
3.5.6 Block (6)

- By using the same procedure used in block (1) and (2), the
loads of block (6) is calculated and are shown in table 40
(3-13).

Load KVA
Streets load 21.3
Ground load 87.8
Building (5) 77
3.5.7 Block (7)

Load KVA
Streets load 27.3
Ground load 21.3
Building (5) 77
3.6 Critical loads

The distribution system is readable when the interruption
period is as small as possible. Therefore, it must be designed in such
away that the continuity of the supply at desert level of quality is
41
satisfied. When the mean source is separated it will causes the
dangerous that it will be required another source and the economics
of these process and available power has to be calculated.

3.6.1 Critical loads of block (1)
Tables (3-15) to (3-17) show the critical loads of each building of this
block.
Table (3.15) the critical loads of building (10C).
Critical load KVA

Building Service 3.015
Elevators 37.5
Fire pump 28
Water bump 18.75
Table (3.16) the critical loads of building (5 +13A)
Critical loads KVA

Elevators 37.8
Fire pump 28
Water bump 18.75
Table (3.17) the critical loads of building (13B).
Critical load KVA

(50%) of Building Service 3.015
Elevators 37.5
Fire pump 28
Water bump 18.75
3.6.2 Critical loads of block (2).

Table (3.18) critical loads of Mall region
Critical load KVA

42
(33%) of lighting 3.11
Elevators 18.75
Fire pump 28
Table (3.19) critical loads of Office
Critical load KVA

Water pump 9.5
Elevators 37.5
(50%) ground 9
Fire pump 28
Table (3.20) critical loads of Hotel
Critical load KVA

Water pump 18.75
Elevator 75
70%ground 22.12
Fire pump 56
3-6-3 Critical loads of block (3).

Table (3.21) Critical loads of building (10C).
Critical load KVA

(50%) of Building 3.015
Service
Elevators 37.5
Fire pump 28
Water bump 18.75
Table (3.22) Critical loads of building (13A+5).

Critical load KVA
(50%) Building Service 2.25

Elevators 37.5
43
Fire pump 28
Water bump 18.75

Table (3.23) Critical loads of building (13B).
Critical load KVA

Service
Elevators 37.5
Fire pump 28
Water bump 18.75

The block consists of two same parts, the critical loads for each
part is as follow:
Table (3.24) Critical loads of building (13A+5).
Critical load K VA
Service
Fire pump 28
Elevators 37.5
Water pump 18.75
Table (3.25) Critical loads of building (13B).
Critical loads K VA
Service
Fire pump 28
Elevators 37.5
Water pump 18.75

The critical loads of buildings of 10, 8, 6, 5 and 4 floors which is 44
connected to each other.
Table (3.26) the critical loads.

Critical loads KVA

Fire pump 28
Elevators 75
Water pump 28.75

- The critical loads of block (6) are the same critical loads of block
(3).

- The critical loads of block (7) are the same critical loads of block
(1).
45

Renewable Energies
Chapter 4
IN THIS CHAPTER:
 Wind Energy
 Solar energy
 Electrical Energy Storage Systems

Renewable Energies Chapter4
4. Introduction to renewable energies

The use of renewable energy sources, such as solar, wind and
hydraulic energies, is very old; they have been used since many
centuries before our time and their applications continued
throughout history and until the "industrial revolution", at which
time, due to the low price of petroleum, they were
abandoned. During recent years, due to the increase in fossil fuel
prices and the environmental problems caused by the use of
conventional fuels, we are reverting back to renewable energy
sources.
Renewable energies are inexhaustible, clean and they can be used in

a decentralised way (they can be used in the same place as they are
produced). Also, they have the additional advantage of being
complimentary, the integration between them being favorable. For
example, solar photovoltaic energy supplies electricity on sunny
days (in general with low wind) while on cold and windy days,
which are frequently cloudy, the wind generators are in position to
supply more electric energy.
The electrical energy produced by photovoltaic power generator or

by a wind generator can be used in two ways: consumed at the time
of generation or stored. In order to use this energy at times other
than daylight hours or on days without wind, it is necessary to
install batteries whose function it is to store the energy produced by
the generator and to maintain the voltage of the installation at a
reasonably constant level.
so the energy storage system" EES" are used.
Historically, EES has played three main roles. First, EES reduces
electricity costs by storing electricity obtained at off-peak times
when its price is lower, for use at peak times instead of electricity
bought then at higher prices. Secondly, in order to improve the
reliability of the power supply, EES systems support users when
power network failures occur due to natural disasters. Their third
role is to maintain and improve power quality, frequency and
voltage. This chapter is concerned with the study of photovoltaic, 47
wind power generators and EES.

4.1Wind Energy
4.1.1 Basic principle of wind energy
The terms "wind energy" or "wind power" describe the process by
which the wind is used to generate mechanical power or electricity.
Wind turbines convert the kinetic energy in the wind into
mechanical power. This mechanical power can be used for specific
tasks (such as grinding grain or pumping water) or a generator can
convert this mechanical power into electricity to power homes,
businesses, schools.
4.1.2 Wind Turbines

Wind turbines, like aircraft propeller blades, turn in the moving air
and power an electric generator that supplies an electric current.
Simply stated, a wind turbine is the opposite of a fan. Instead of
using electricity to make wind, like a fan, wind turbines use wind to
make electricity. The wind turns the blades, which spin a shaft,
which connects to a generator and makes electricity.
4.1.3 Types of wind turbines

4.1.3.1. horizontal-axis wind turbines:
In which the axis of rotation is horizontal with respect to the

ground (and roughly parallel to the wind stream)
4.1.3.2vertical-axis wind turbines:
In which the axis of rotation is vertical with respect to the ground

(and roughly perpendicular to the wind stream)
48

Fig 4-1 wind turbine configuration
4.1.4 Parts of a Horizontal Axis Wind Turbine

1. Anemometer: Measures the wind speed and transmits wind
speed data to the controller.
2. Brake: A disc brake which can be supplied mechanically
electrically or hydraulically to stop the rotor in emergencies.
3. Controller: The controllers starts up the machine at wind speed
of about 8 to 16miles per hour(mph) and shuts off the machine at
about 65mph. Turbines cannot operate at wind speed above about
65mph because of their generators could over heat.
4. Gear box: Gears connect the low-speed shaft to the high speed
shaft and increase the rotational speeds from about 30 to 60
rotations per minute(rpm) to about 1200 to 1500 rpm, the rotational
speed required by most generators to produce electricity. The gear
box is a costly and heavy part of the wind turbine.
5. Pitch: Blades are turned, or pitched, out of the wind to keep the
rotor from turning in winds that are too high or too low to produce
electricity.
6. Wind vane: Measures wind direction and communicates with the
yaw drive to orient the turbine properly with respect to the wind.
7. Yaw drive: Upwind turbines face into the wind; the yaw drive is
49
used to keep the rotor facing into the wind as the wind direction
changes. Downwind turbines don’t require a yaw drive, the wind
blows the rotor downwind.
8. Yaw motor: Powers the yaw drive.
Fig 2-2 horizontal axis wind turbine
4.1.5 Types of Generators used for Wind

Turbines
4.1.5.1 Induction Generator
An induction generator is a type of electrical generator that is
mechanically and electrically similar to an induction motor.
Induction generators produce electrical power when their shaft is
rotated faster than the synchronous frequency of the equivalent
induction motor. Induction generators are often used in wind
turbines and some micro hydro installations. Induction generators
are mechanically and electrically simpler than other generator
types. They are also more rugged, requiring no brushes or
commutator.
Induction generators are not self-exciting, meaning they require an
external supply to produce a rotating magnetic flux, the power
required for this is called reactive current. The external supply can
be supplied from the electrical grid or from the generator itself,
once it starts producing power or can you can use a capacitor bank
to supply it. The rotating magnetic flux from the stator induces 50
currents in the rotor, which also produces a magnetic field. If the
rotor turns slower than the rate of the rotating flux, the machine acts

like an induction motor. If the rotor is turned faster, it acts like a

generator, producing power at the synchronous frequency. In the
United States it would be 60 Hz.
The common down side of using an induction generator in a wind
turbine is gearing. Typically you need an induction motors to run
1500+ RPM to meet the synchronous so a gearing is almost always
needed.
4.1.5.2 Permanent Magnet Alternators:

Permanent magnets alternators (PMA) have one set of
electromagnets and one set of permanent magnets. Typically the
permanent magnets will be mounted on the rotor with the
electromagnets on the stator. Permanent magnet motor and
generator technology has advance greatly in the past few years with
the creation of rare earth magnets (neodymium, samarium-cobalt,
and alnico). Generally the coils will be wired in a standard three
phase wye or delta.
Permanent magnet alternators are can be very efficient, in the range
of 60%-95%, typically around 70% though. As a generator they do
not require a controller as a typical three phase motor would need.
It is easy to rectify the power from them and charge a battery bank
or use with a grid tie.
It is easy to build a permanent magnet alternator, even for
beginners. This is a common choice for home builders.
Note: Car alternators are not PMA but actually have a field coil
instead of permanent magnets, and are typically very inefficient
around 50%. They typically need to be spun 1500+RPM to get any
real power out of them, but with a belt or gear arrangement can still
do a decent job.
4.1.5.3 Brushed DC Motor:
Brushed DC Motors are commonly used for home built wind
turbines. They are backwards from a permanent magnet generator.
On a brushed motor, the electromagnets spin on the rotor with the
power coming out of what is known as a commutator. This does
cause a rectifying effecting outputting lumpy DC, but this is not an 51
efficient way to “rectify” the power from the windings, it is used
because it’s the only way to get the power out of the rotor. A good

brushed motor can reach a good efficiency, but are typically at most
70%.
There are many great advantages to using a brushed motor. One of
the biggest reasons is because typically you can find one not
requiring any gearing and still get a battery charging voltage in light
wind. They are also quite easy to find, they can be purchased from
eBay, surplus supply stores, industrial supply stores, and can find
them on different things that might get thrown away or given away
(like a treadmill).
4.1.6 Modeling the Power Generated by a

Turbine
The total power delivered to a wind turbine can be estimated by
taking the derivative of the wind's kinetic energy. This results in the
following expression:
(1)
where A = swept area of turbine blades, in m2
ρ = air density, in kg/m3
u = wind speed, in m/s
The process of converting wind power to electrical power results in
efficiency losses, as described in the diagram below.
The electrical power output of a practical wind turbine can be

described using the following equation:
(2)
Where C tot = overall efficiency = Cp Ct Cg
Overall efficiency is typically between 0.3 and 0.5, and varies with
both wind speed and rotational speed of the turbine. For a fixed
rotational speed, the turbine operates most efficiently at what's
known as the rated wind speed. At this wind speed, the electrical 52
power generated by a wind turbine is near its maximum (Per), and
overall efficiency is denoted C tot R.

(3)
For a fixed rotational speed, the electrical power output of a wind
turbine can be estimated using the profile below.
Where
u c = cut-in speed, the speed at which the electrical power output
rises above zero and power production starts.
u r = rated wind speed.
u f = furling wind speed, the speed at which the turbine is shut
down to prevent structural damage.
4.1.7 Wind power system:

4.1.7.1 Fixed speed wind turbine
For the fixed-speed wind turbine, the induction generator is directly
connected to the electrical grid according to the figure. The rotor
speed of the fixed-speed wind turbine is in principle determined by
a gear box and the pole-pair number of the generator.
53

Fig 4-3 fixed speed wind turbine
4.1.7.2 variable speed wind turbine

The system presented in the next figure consist of a wind turbine
equipped with a converter connected to the stator of the generator.
the generator could either be a cage- bar induction generator or a
synchronous generator. Synchronous generator or permanent-
magnet synchronous generator can be designed with multiple poles
which imply that there is no need for a gear box.
Fig 4-4 variable speed wind turbine
4.1.7.3 variable speed wind turbine with DFIG

This system consists of a wind turbine with doubly-fed induction
generator (DFIG). This means that the stator is directly connected
to the grid while the rotor winding is connected via slip ring tos to
54
a converter.

Fig 4-5 variable speed wind turbine with DFIG
4.1.8 Control Methods

You can use different control methods to either optimize or limit
power output. You can control a turbine by controlling the
generator speed, blade angle adjustment, and rotation of the entire
wind turbine. Blade angle adjustment and turbine rotation are also
known as pitch and yaw control, respectively. A visual
representation of pitch and yaw adjustment is shown in Figures
6and 7.
55
Fig 4-6 Pitch Fig-7 yaw adjustment

The purpose of pitch control is to maintain the optimum blade angle

to achieve certain rotor speeds or power output. You can use pitch
adjustment to stall and furl, two methods of pitch control. By
stalling a wind turbine, you increase the angle of attack, which
causes the flat side of the blade to face further into the wind.
Furling decreases the angle of attack, causing the edge of the blade
to face the oncoming wind. Pitch angle adjustment is the most
effective way to limit output power by changing aerodynamic force
on the blade at high wind speeds.Yaw refers to the rotation of the
entire wind turbine in the horizontal axis. Yaw control ensures that
the turbine is constantly facing into the wind to maximize the
effective rotor area and, as a result, power. Because wind direction
can vary quickly, the turbine may misalign with the oncoming wind
and cause power output losses. You can approximate these losses
with the following equation:
EQ 6: ∆P=α cos(ε)
Where ∆P is the lost power and ε is the yaw error angle.
The final type of control deals with the electrical subsystem. You can
achieve this dynamic control with power electronics, or, more
specifically, electronic converters that are coupled to the generator.
The two types of generator control are stator and rotor. The stator
and rotor are the stationary and nonstationary parts of a generator,
respectively. In each case, you disconnect the stator or rotor from the
grid to change the synchronous speed of the generator independently
of the voltage or frequency of the grid. Controlling the synchronous
generator speed is the most effective way to optimize maximum
power output at low wind speeds.
Figure 8 shows a system-level layout of a wind energy conversion
system and the signals used. Notice that control is most effective by
adjusting pitch angle and controlling the synchronous speed of the
generator.
56

4.1.9 Advantages of wind energy

1. The wind is free and with modern technology it can be captured
efficiently.
2. Once the wind turbine is built the energy it produces does not
cause greenhouse gases or other pollutants.
3. Although wind turbines can be very tall each takes up only a
small plot of land. This means that the land below can still be used.
This is especially the case in agricultural areas as farming can still
continue.
4. Many people find wind farms an interesting feature of the
landscape.
5. Remote areas that are not connected to the electricity power grid
can use wind turbines to produce their own supply.
6. Wind turbines have a role to play in both the developed and third
world.
7. Wind turbines are available in a range of sizes which means a
vast range of people and businesses can use them. Single
households to small towns and villages can make good use of range
of wind turbines available today.
4.1.10 Disadvantages of wind energy

1. The strength of the wind is not constant and it varies from zero to
storm force. This means that wind turbines do not produce the same
amount of electricity all the time. There will be times when they
produce no electricity at all.
2. Many people feel that the countryside should be left untouched,
without these large structures being built. The landscape should left
in its natural form for everyone to enjoy.
3. Wind turbines are noisy. Each one can generate the same level of
noise as a family car travelling at 70 mph.
4. Many people see large wind turbines as unsightly structures and
not pleasant or interesting to look at. They disfigure the countryside
and are generally ugly.
5. When wind turbines are being manufactured some pollution is
produced. Therefore wind power does produce some pollution. 57
6. Large wind farms are needed to provide entire communities with
enough electricity. For example, the largest single turbine available
today can only provide enough electricity for 475 homes, when
running at full capacity. How many would be needed for a town of

100 000 people?
58

Turbine technical specification
59

4.1.11Power calculation for one day

Of wind turbine
hour v(mls) vci vco vr pr po Max po
1am 7 3.5 20 13 1650000 607894.7 1476316
2am 7 3.5 20 13 1650000 607894.7
3am 7 3.5 20 13 1650000 607894.7
4am 7 3.5 20 13 1650000 607894.7
5am 8 3.5 20 13 1650000 781578.9
6am 8 3.5 20 13 1650000 781578.9
7am 8 3.5 20 13 1650000 781578.9
8am 9 3.5 20 13 1650000 955263.2
9am 8 3.5 20 13 1650000 781578.9
10am 8 3.5 20 13 1650000 781578.9
11am 8 3.5 20 13 1650000 781578.9
12pm 8 3.5 20 13 1650000 781578.9
1pm 8 3.5 20 13 1650000 781578.9
2pm 8 3.5 20 13 1650000 781578.9
3pm 9 3.5 20 13 1650000 955263.2
4pm 12 3.5 20 13 1650000 1476316
5pm 12 3.5 20 13 1650000 1476316
6pm 10 3.5 20 13 1650000 1128947
7pm 9 3.5 20 13 1650000 955263.2
8pm 8 3.5 20 13 1650000 781578.9
9pm 8 3.5 20 13 1650000 781578.9
10pm 8 3.5 20 13 1650000 781578.9
11pm 7 3.5 20 13 1650000 607894.7 60
12am 8 3.5 20 13 1650000 781578.9

4.2Solar energy
The energy in solar irradiation comes in the form of electromagnetic
waves of a wide spectrum. Longer wavelengths have less energy (for
instance infrared) than shorter ones such as visible light or UV.
The spectrum can be depicted in a graph, the spectral distribution,
which shows the relative weights of individual wavelengths plotted
over all wavelengths, measured in W / m (wavelength).
The diagram displays the spectrum of a sun ray just outside the entry
into the earth’s atmosphere. The peak of the spectrum is within the
visible spectrum, but there are still significant amounts of shorter and
longer wavelengths present.
4.2.1Insolation and Total Solar Irradiance

Total solar irradiance is defined as the amount of radiant energy
emitted by the Sun over all wavelengths that fall each second on 11
ft2 (1 m2) outside Earth's atmosphere irradiance is defined as the
amount of electromagnetic energy incident on a surface per unit
time per unit area.
Insolation is the amount of solar energy that strikes a iven area over
a specific time, and varies with latitude or the seasons.
61
The average amount of energy from the Sun per unit area that
reaches the upper regions of Earth's atmosphere is known as the

solar constant; its value is approximately 1,367 watts per square

meter.
The deserts of Africa, the Sahara, Namib Desert and the Arabian
Peninsula, are among the places with highest irradiation on earth,
especially 1,000km south of the Mediterranean where the annual
global irradiation is about twice that of southern Germany.
4.2.2Photovoltaic cells
The Principles of Photovoltaic cells
PV cells are made of at least two layers of semiconductor material.
One layer has a positive charge" P-type", the other layer has
negative charge" N-type" with different electrical properties, joined
together. The joint between these two semiconductors is called the
"P-N junction."
Sunlight striking the photovoltaic cell is absorbed by the cell. The
energy of the absorbed light generates particles with positive or 62
negative charge (holes and electrons), which move about or shift

freely in all directions within the cell.
The electrons (-) tend to collect in the N-type semiconductor, and

the holes (+) in the P-type semiconductor. Therefore, when
anexternal load, such as an electric bulb or an electric motor, is
connected between the front and back electrodes, electricity flows
in the cell.
Photovoltaic cells Construction of
the basic cell construction (monocrystalline silicon cell).
4.2.3PV connection
PV cells are interconnected together in a package called a module.
When two modules are wired together in series, their voltage is
doubled while the current stays constant.
When two modules are wired in parallel, their current is doubled
while the voltage stays constant.
To achieve the desired voltage and current, modules are wired in
series and parallel into what is called a PV array.
63

4.2.4Types of cells
4.2.4.1Crystalline silicon
Crystalline cells have been in service the longest and exhibit
outstanding longevity. Cells developed almost 40 years ago are still
operating and most manufacturers offer 10-year or longer
warranties on crystalline cells. There are two sub-categories of
crystalline cells – single crystal and polycrystalline. They both
perform similarly. The efficiency of crystalline cells is around 13%.
4.2.4.2 Amorphous silicon
Amorphous silicon is a recent technology for solar cells. It is
cheaper to produce and offers greater flexibility, but their efficiency
is half of the crystalline cells and they will degrade withuse.
These types of cells will produce power in low light situations.
This technology is expected to improve application ossibilities far
exceeding crystalline technology. Currently; the best choice for
solar cells will be the crystalline variety.
64

4.2.5Two approaches for using PV’s: stand-

alone and grid-interface.
4.2.5.1Stand-alone system
Requires batteries to store power for the times when the sun is not
shining .Does not use electric utility power.
The stand-alone system is termed a “separate system” by the electric
utility. However, a “separate system” in the utility’s terminology can
exist in a home that also has utility power as long as they are completely
separated.
4.2.5.2Grid-interface system
Uses power from the central utility when needed and supplies surplus
home-generated power back to the utility. Termed a “parallel” system by
the utility.
The following information presents a partial overview

of the guidelines often needed to interface with the
grid:
 Technical data and information must be supplied to the power

company. This includes physical layout drawings, equipment
specifications and characteristics, coordination data (this pertains to
the parts that will achieve the link to the utility system), test data on
the equipment, synchronizing methods, operating and instruction
manuals, and maintenance schedule and records.
 Interconnection equipment is installed and maintained by the
customer.
 Maintenance records must be provided to Power Company if
requested. Protective equipment must be maintained by the
customer every 2 years or as required by Power Company.
 The customer must provide their own protective devices for their
system.
 Extra costs incurred by the power company in the interface
arrangement must be borne by the customer.
 The PV system can operate only after written approval is received
from the power company.
 The customer and the power company must have agreed upon
65
safety procedures.

The interface between the home produced power can be metered in

a manner that when power is produced by the PV’s and sent into the
grid the meter will run backwards.
When power is brought in from the grid the meter will run in the
regular direction. This is called “net metering”. Either approach
(stand-alone or grid interface) can be done partially; with PV’s
being used in conjunction with a generator in a stand-alone system,
or with the central grid power serving as a primary power source in
a grid-interface system.
4.2.6Steps in designing a PV system.

4.2.6.1 Calculate the Electrical Load
Examine the uses of energy in a home in three categories (thermal
or heat energy, electrical energy, and refrigeration), conservation
opportunities can then be isolated in each category that can affect
overall electrical consumption.
a-Thermal energy requirement for heating living
spaces, water, and cooking.
Best accomplished by non-electrical fuels such as solar, gas, wood,
and others. Electric space heating, water heating, and cooking
require an enormous amount of electricity. It is not practical to use
photovoltaics to create electricity for these purposes. Solar energy
can be used in other forms such as passive and active solar space
heating and solar water heating more efficiently. Gas can also be
used for the thermal loads more economically and efficiently than
electricity.
b-Electrical loads (lighting, appliance and equipment
operation)
Should be done with the most conserving items that can accomplish
the task. Highly energy efficient lighting products are readily
available and the energy efficiency of appliances can be easily
compared for the best choices.
Best application for PVs is in this category.
66
c-Refrigeration for air conditioning and food
preservation.

Consumes proportionally enormous amounts of electrical energy

making PV power very costly for these tasks. Gas powered air
conditioning is available as an alternative.
For food preservation, there are gas refrigerators and two
manufacturers of very high efficiency electrical refrigerators and
freezers.
4.2.6.2Size the PV System
Different size PV panels will produce different amounts of power.
The rated output wattage of the panel is the amount of watts the
panel will create in one hour of direct sun. For our area, multiply
the rated wattage by 5.1 to get the average amount produced in one
day. The 5.1 factor is the viable operating hours per day and
accounts for the fact that there will be more sun available in the
summer and less in the winter.
4.2.7PV Subsystems – Inverters, Controllers,

and Wiring Inverters
Conventional appliances and equipment and utility-supplied power
use alternating current (AC) power and PV systems produce direct
current (DC) power. Inverters are required to convert the power
from the PV’s from DC to AC. Recently produced inverters are
reliable and efficient. They are also a major cost for the project
starting at over $1,000 for a size that will accommodate a residence.
For practical reasons, including electrical code compliance and

financing, it is best to have a conventional (AC) electrical
distribution system in the house. This will permit the use of
appliances, equipment, and lighting that is commonly available.
4.2.7.1Charge controllers
Regulate the voltage entering batteries to avoid overcharging the
batteries.
Available in different capacities and must be selected to match the
system.
Prevents losses of power back through the panels at night.
67
4.2.7.2Wiring
Some direct current (DC) equipment may be desirable to operate in
a home. DC appliances and equipment, although initially more
costly than their AC counterparts, will use less power to operate. In

some cases, such as pumps, the DC motors are much more efficient.
When DC wiring is going to be used in a home, a heavier wire is
required. Generally, #10 wire is best for direct current applications
but larger wire may be necessary if the wire runs are quite long.
Tables are available in the manuals offered by companies listed in
the Resources section.
4.2.8MountingPV panels
PV arrays must be placed to receive the most sunlight. A 45-degree
slope to the panels with a south orientation is best. The 45-degree
slope will help offset the shorter winter day by bringing the panels
closer to perpendicular to the lower winter sun.
There are several ways to mount the panels – fixed, fixed with
adjustable tilt angles, manual tracking, passive tracking, and active
trackers. All of these mounting approaches can be placed on the
ground or on a roof except for some active trackers which are pole
mounted and thus more suited for a ground mount.
Fixed mounts are the least costly and lowest energy producing
mounting systems. A metal frame suited for outdoor conditions is
best. PV panels will substantially outlive the best wood racks.
The fixed mount with adjustable tilt angles and manual tracking
mounts will require manually changing the angle of the PV panels
either several times a day (manual tracking) and/or seasonal
adjustments to keep the panels as close to perpendicular as possible
to the sun (tilt angle adjustments).
Trackers are useful if the site is appropriate. There needs to be no

obstacles in the east and west that will block the sun since the
trackers will orient the PV panels to face the sun from early
morning to late afternoon. Passive trackers are typically freon
activated to track the sun from east to west only (there is no
automatic tilt angle change). Active trackers draw a very small
amount of power from the PV panels (as low as one watt) and
mechanically track from east to west and adjust to the proper tilt
angle. The passive trackers will increase the panels output from 40-
50%. Active trackers will improve panel output by as much as 60%. 68
However, it is important to realize that the largest gains for the

trackers occurs during the longest days of summer. There are not
large gains in the winter.
4.2.9Batteries
Batteries are the best method of storing energy from a PV system
for the periods when the sun is not shining. (This is for stand-alone
or non -grid connected systems.) The information from calculating
the daily load will be needed for determining the battery sizing.
4.2.10PV Output Power
The basic element of a solar energy conversion system is the PV
module/cell, which absorbs photons of light from the incident solar
radiation, and releases electrons to provide a DC current to a closed
electrical circuit. The rating of a PV module is expressed in peak-
watt and is equal to the maximum power produced by a module
under standard test conditions (STC).
However, a single PV module has limited potential to provide
power at high voltage or high current levels. It is thus mandatory to
connect PV modules in series and parallel, in a form of array, in
order to scale-up the voltage and current to reach a given level of
electrical power.
The manufacturers of PVs usually provide the characteristic of their
PV module under STC by
specifying Isc (short circuit current in A), Voc (open-circuit
voltage in V),IMPP (current at maximum power point in A), VMPP
(voltage at maximum power point in ),and NOT(nominal operating
temperature of cell in o C).
69

A typical graphical presentation of the current-voltage and power-

voltage characteristics of a PV module is shown in figure 3-12. This
current-voltage characteristic is valid for a particular radiation level
and ambient temperature. The short circuit current is directly
proportional to the solar radiation, whereas the voltage is inversely
proportional to the temperature. Moreover, most of the PV modules
are equipped with a maximum power point tracker which helps the
PV system to operate near the knee of the I-V curve all day long to
generate maximum power from the PV in different weather
conditions.
70

Power calculation of pv system

Zone"1" {Block1} {Block7} {Mall} {office block2}
Zone"2"{Block3} {Block6} {Hotel block 2}
Zone"3"{Block4} {Block 5}
Block 1 = Block 3=Block 7=Block 6
{B5,10C,13B,13C}
{B5} : area =820

number of modules = area / area of module = 503
power of modules = power of one module * no of modules
=76959 Watt =96198.75 VA =0.09619875 MVA
{10C}: area =795
Number of modules =488=74664Watt =0.09333MVA
Power of modules
{13B}:area =910
number of modules =558=85374Watt =0.1067175MVA
power of modules
{13A}:area=680
number of modules =417=63801Watt =0.07975MVA
Total power of PV of Block "1" = 375.99625 KVA
Block"2"
{office1,office2,hotel1,hotel2,hotel3,hotel4}
Office1 : 1bulding area=910
number of modules =558
power of modules = 85374Watt =0.1067175MVA
Office2 : 2bulding area=445 for each building
71
power of modules = 41769Watt

power of 2 buildings = 83538 Watt=0.0144228MVA

Hotel 1 : 2bulding area=590 for each building
Hotel 2 : area=40
power of modules= 3672 Watt=4.59KVA
Hotel 3 : area=80
power of modules= 7497 Watt= 9.37123KVA
Hotel 4 : 2bulding area=540 for each building
Total power of PV of Block "2" = 400.17403 KVA

Block" 4"
{B5,13B,13C}
{B5} : area =820
number of modules = 503
power of modules =76959 Watt =0.09619875 MVA
{13B}:area =910
power of modules=85374Watt =0.1067175MVA
{13A}:area=680
power of modules =63801Watt =0.07975MVA
Total power of PV of Block "4" = 282.66625 KVA 72

Block" 5"
area = 2117
power of modules=198594Watt =0.2482425MVA
Mall: area=350
power of modules =32742Watt =0.0409275MVA
zone "1"={Block1}+ {Block7} +{Mall}+ {office block2}

=0.1067175MVA +0.0144228MVA+0.0409275MVA 375.99625
KVA* 2 =914.0603KVA=0.9140603MVA
Zone"2"= {Block3}+ {Block6}+ {Hotel block 2}
=2*375.99625KVA+0.138465MVA+4.59KVA+9.37123KVA+0.126
6075MVA =1031.02623kVA=1.031MVA
Zone"3"={Block4} + {Block 5}
282.66625KVA+0.2482425MVA=530.90875KVA=0.53090875MVA
Table 4.1 Module specifications
73

4.3.Electrical Energy Storage Systems

1. Characteristics of electricity
Two characteristics of electricity lead to issues in its use, and by the
same token generate the market needs for EES. First, electricity is
consumed at the same time as it is generated. An imbalance
between supply and demand will damage the stability and quality
(voltage and frequency) of the power supply even when it does not
lead to totally unsatisfied demand. The second characteristic is that
the places where electricity is generated are usually located far
from the locations where it is consumed much power flow may
happen to be concentrated into a specific transmission line and this
may cause congestion. if a failure on a line occurs (because of
congestion or any other reason) the supply of electricity will be
interrupted.
4.3.1Electricity and the roles of EES

4.3.1.1 High generation cost during peak demand Periods
Power demand varies from time to time and the price of electricity
changes accordingly. The price for electricity at peak demand
periods is higher and at off peak periods lower. This is caused by
differences in the cost of generation in each period. During the off-
peak period when less electricity is consumed, costly types of
generation can be stopped. This is a chance for owners of EES
systems to benefit financially. With high PV and wind penetration
in some regions, cost-free surplus energy is sometimes available.
This surplus can be stored in EES and used to reduce generation
costs. Conversely, from the consumers’ point of view, EES can
lower electricity costs since it can store electricity bought at low
off-peak prices and they can use it during peak periods in the place
of expensive power. Consumers who charge batteries during off-
peak hours may also sell the electricity to utilities or to other 74
consumers during peak hours.

4.3.1.2Need for continuous and flexible Supply

If the proper amount of electricity cannot be provided at the time
when consumers need it, the power quality will deteriorate and at
worst this may lead to a service interruption. Renewable energy
facilities such as solar and wind do not possess both a kW function
and a frequency control function unless they are suitably modified.
Such a modification may be a negative power margin (i.e.
decreasing power) or a phase shift inverter. EES is expected to be
able to compensate for such difficulties with a kW function and a
frequency control function. Stationary batteries have been utilized
to support renewable energy output with their quick response
capability.
4.3.1.3Long distance between generation and consumption

Consumers’ locations are often far from power generating facilities,
and this sometimes leads to higher chances of an interruption in the
power supply. Network failures due to natural disasters (e.g.
lightning, hurricanes) and artificial causes (e.g. overload,
operational accidents) stop electricity supply and potentially
influence wide areas. EES will help users when power network
failures occur by continuing to supply power to consumers. One of
the representative industries utilizing EES is semi-conductor and
LCD manufacturing, where a voltage sag lasting for even a few
milliseconds impacts the quality of the products. A UPS system,
built on EES and located at a customer’s site, can keep supplying
electricity to critical loads even when voltage sag occurs due to, for
example, a direct lightning strike on distribution lines. A portable
battery may also serve as an emergency resource to provide power
to electrical appliances.
4.3.1.4Congestion in power grids

EES established at appropriate sites such as substations at the ends
of heavily-loaded lines can mitigate congestion, by storing
75
electricity while transmission lines maintain enough capacity and
by using it when lines are not available due to congestion.

4.3.1.5Transmission by cable
Electricity always needs cables for transmission, and supplying
electricity to mobile applications and to isolated areas presents
difficulties. EES systems such as batteries can solve this problem
with their mobile and charge/discharge capabilities. In remote
places without a power grid connection recharging an electric
vehicle may present a challenge, but EES can help realize an
environmentally friendly transport system without using
conventional combustion engines.
4.3.2Emerging needs for EES

There are two major emerging market needs for EES as a key
technology: to utilize more renewable energy and less fossil fuel,
and the future Smart Grid.
4.3.2.1More renewable energy, less fossil Fuel

On-grid areas
In on-grid areas, the increased ratio of renewable generation may
cause several issues in the power grid (see Figure 1). First, in power
grid operation, the fluctuation in the output of renewable generation
makes system frequency control difficult, and if the frequency
deviation becomes too wide system operation can deteriorate.
Conventionally, frequency control is mostly managed by the output
change capability of thermal generators. When used for this
purpose thermal generators are not operated at full capacity, but
with some positive and negative output margin (i.e. increases and
decreases in output) which is used to adjust frequency, and this
implies inefficient operation. With greater penetration of renewable
generation this output margin needs to be increased, which
decreases the efficiency of thermal generation even more.
Renewable generation units themselves in most cases only supply a
negative margin. If EES can mitigate the output fluctuation, the
76
margins of thermal generators can be reduced and they can be
operated at a higher efficiency. Secondly, renewable energy output

is undependable since it is affected by weather conditions. Some

measures are available to cope with this. One is to increase the
amount of renewable generation installed, i.e. provide overcapacity,
so that even with undependability enough power can be secured.
Another is to spread the installations of renewable generators over a
wide area, to take advantage of weather conditions changing from
place to place and of smoothing effects expected from the
complementarily of wind and solar generators. These measures are
possible only with large numbers of installations and extension of
transmission networks. Considering the cost of extra renewable
generation and the difficulty of constructing new transmission
facilities, EES is a promising alternative measure.
Off-grid areas
In off-grid areas where a considerable amount of energy is
consumed, particularly in the transport sector, fossil energy should
be replaced with less or non-fossil energy in such products as plug
in hybrid electric vehicles (PHEVs) or electric vehicles (EVs) (see
Figure 1). More precisely, fossil fuels should be replaced by low-
carbon electricity produced mainly by renewable generation. The
most promising solution is to replace petrol or diesel-driven cars by
electric ones with batteries. In spite of remaining issues (short
driving distance and long charging time) EES is the key technology
for electric vehicles.
Smart Grid uses

EES is expected to play an essential role in the future Smart Grid.
Some relevant applications of EES are described below. First, EES
installed in customer-side substations can control power flow and
mitigate congestion, or maintain voltage in the appropriate range.
Secondly, expected for EES is as the energy storage medium for
Energy Management Systems (EMS) in homes and buildings. With
a Home Energy Management System, for example, residential
customers will become actively involved in modifying their energy 77
spending patterns by monitoring their actual consumption in real
time.

Fig 4.3.1 – Problems in renewable energy installation and possible solutions
4.3.3The roles of electrical energy storage

technologies
Generally the roles for on-grid EES systems can be described by
the number of uses (cycles) and the duration of the operation, as
shown in Figure 2. For the maintenance of voltage quality (e.g.
compensation of reactive power), EES with high cycle stability and
short duration at high power output is required; for time shifting on 78

the other hand longer storage duration and fewer cycles are needed.
The following sections describe the roles in detail.
Fig 4.3.2 – Different uses of electrical energy storage in grids, depending on

the frequency and duration of use
4.3.3.1The roles from the viewpoint of a utility

1) Time shifting
Utilities constantly need to prepare supply capacity and
transmission/distribution lines to cope with annually increasing
peak demand, and consequently develop generation stations that
produce electricity from primary energy. For some utilities
generation cost can be reduced by storing electricity at off-peak
times, for example at night, and discharging it at peak times. If the
gap in demand between peak and off-peak is large, the benefit of
storing electricity becomes even larger. Using storage to decrease
the gap between daytime and night-time may allow generation
output to become flatter, which leads to an improvement in
operating efficiency and cost reduction in fuel.
2) Power quality
A basic service that must be provided by power utilities is to keep
supply power voltage and frequency within tolerance, which they
can do by adjusting supply to changing demand. Frequency is
controlled by adjusting the output of power generators; EES can 79
provide frequency control functions. Voltage is generally controlled
by taps of transformers, and reactive power with phase modifiers.
EES located at the end of a heavily loaded line may improve

voltage drops by discharging electricity and reduce voltage rises by
charging electricity.
3) Making more efficient use of the network

In a power network, congestion may occur when
transmission/distribution lines cannot be reinforced in time to meet
increasing power demand. In this case, large-scale batteries
installed at appropriate substations may mitigate the congestion and
thus help utilities to postpone or suspend the reinforcement of the
network.
4) Isolated grids
Where a utility company supplies electricity within a small, isolated
power network, for example on an island, the power output from
small-capacity generators such as diesel and renewable energy must
match the power demand. By installing EES the utility can supply
stable power to consumers.
5) Emergency power supply for protection and control equipment

A reliable power supply for protection and control is very
important in power utilities. Many batteries are used as an
emergency power supply in case of outage.
4.3.3.2The roles from the viewpoint of consumers

1) Time shifting/cost savings
Power utilities may set time-varying electricity prices, a lower price
at night and a higher one during the day, to give consumers an
incentive to flatten electricity load. Consumers may then reduce
their electricity costs by using EES to reduce peak power needed
from the grid during the day and to buy the needed electricity at
off-peak times.
2) Emergency power supply

Consumers may possess appliances needing continuity of supply, 80
such as fire sprinklers and security equipment. EES is sometimes
installed as a substitute for emergency generators to operate during

an outage. Semiconductor and liquid-crystal manufacturers are

greatly affected by even a momentary outage (e.g. due to lightning)
in maintaining the quality of their products. In these cases, EES
technology such as large-scale batteries, double-layer capacitors
and SMES can be installed to avoid the effects of a momentary
outage by instantly switching the load off the network to the EES
supply. A portable battery may also serve in an emergency to
provide power to electrical appliances.
4.3.3.3The roles from the viewpoint of generators of

renewable energy
1) Time shifting
Renewable energy such as solar and wind power is subject to
weather, and any surplus power may be thrown away when not
needed on the demand side. Therefore valuable energy can be
effectively used by storing surplus electricity in EES and using it
when necessary; it can also be sold when the price is high.
2) Effective connection to grid
The output of solar and wind power generation varies greatly

depending on the weather and wind speeds, which can make
connecting them to the grid difficult. EES used for time shift can
absorb this fluctuation more cost-effectively than other, single-
purpose mitigation measures (e.g. a phase shifter)
4.3.4Types and features of energy storage

systems
4.3.4.1Classification of EES systems
A widely-used approach for classifying EES systems is the
determination according to the form of energy used. In Figure 3
EES systems are classified into mechanical, electrochemical,
81
chemical, electrical and thermal energy storage systems.

Fig 4.3.3 – Classification of electrical energy storage systems according to energy

form
4.3.4.2 Mechanical storage system

The most common mechanical storage systems are pumped
hydroelectric power plants (pumped hydro storage, PHS),
compressed air energy storage (CAES) and flywheel energy storage
(FES).
4.3.4.3Electrochemical storage Systems

Secondary batteries
Lead acid battery (LA)
Nickel cadmium and nickel metal hydride battery (NiCd, NiMH)
Lithium ion battery (Li-ion)
Metal air battery (Me-air)
Sodium sulphur battery (NaS)
Sodium nickel chloride battery (NaNiCl)
Flow batteries.
Redox flow battery (RFB)
Hybrid flow battery (HFB)
82

Chemical energy storage

Hydrogen (H2)
Synthetic natural gas (SNG)
Electrical storage systems

Double-layer capacitors (DLC)
Superconducting magnetic energy storage (SMES)
4.3.4.4Thermal storage systems
4.3.5Configurations of EES
Energy storage systems can be replaced off-line, in a line-
interactive mode, or on-line to deal with power quality problems
4.3.5.1Off-line systems
Off-line (Also called standby) energy storage systems (Figure.4)
are cost-effective for small, less critical, stand-alone applications
such as isolated PCs and peripherals. However, when an outage
occurs in the utility supply, this configuration may not be able to
switch to its storage power supply fast enough to prevent
disturbances in highly sensitive equipment. If filters are present,
standby systems will protect against most transients by limiting
excess voltage, but their ability to protect against sags and surges is
significantly less than on-line or line-interactive designs.
Fig4.3.4.Off-Line Configuration of Energy Storage Systems.
83

4.3.5.2Line-interactive systems
Line-interactive systems (Figure.5) provide highly effective power
conditioning and energy storage backup. Their voltage boost
circuitry and fast acting transfer switches protect against voltage
sags and surges and provide extremely quick response to
disturbances. Transfer switches with response times of ~1/4 power
cycle provide adequate protection for the most sensitive devices.
The energy efficiency of line-interactive storage system is higher
than that of on-line systems and becomes an important cost-saving
advantage when protecting hundreds of kilowatts of critical loads.
Fig 4.3.5.Line-Interactive Configuration of Energy Storage Systems.
4.3.5.3On-line systems
The on-line configuration (Figure.6) provides the highest level of
protection for critical loads. Off-line and line-interactive storage systems
reduce the impact of transients, surges, and sags by clipping the peaks,
boosting power, or switching to storage backup. In contract, on-line
energy storage systems regenerate the sine wave and do not involve
switching. The configuration protects against all utility disturbances
because the system completely isolates the load from the utility
supply at all times. Since on-line systems continuously condition
input supply, they have relatively large parasitic losses.
84

Fig 4.3.6.On-Line Configuration of Energy Storage Systems.
4.3.6 Choosing the Battery Type
For load leveling purposes, advanced batteries are required. These

batteries should have the following features. high efficiency, 70-
75%; high cycle life. 3000-4000 cycles: discharge should be at
constant power for 5-8 hours; low demand cost ($/MW) and low
capacity cost ($/MWh) although all of these criteria are not met by
any of the existing batteries. the following provide good choices:
1. Sodium-Sulfur,
2. Zinc-Bromine,
3. Hydrogen-Nickels. and
4 Lead-acid
Out of the above four only the lead-acid battery has been the front
runner. A cycle life of 1000-1500 may easily be reached with the
present technology.
85

4.3.7New trends in applications
Renewable energy generation

In order to solve global environmental problems, renewable
energies such as solar and wind will be widely used. This means
that the future energy supply will be influenced by fluctuating
renewable energy sources – electricity production will follow
weather conditions and the surplus and deficit in energy need to be
balanced. One of the main functions of energy storage, to match the
supply and demand of energy (called time shifting), is essential for
large and small-scale applications.
Decentralized storage systems for increased self-consumption of

PV energy (kWh class)
With the increasing number of installed PV systems, the low-
voltage grid is reaching its performance limit. Figure 3-7 shows an
example of system design.
Fig 4.3.7 .PV system designed for energy self-consumption
To provide a consumer-friendly system at low cost, maintenance

cost in particular needs to be low and the most important factor for
stationary batteries is still the price per kWh. Currently for this
application lead acid batteries are the most common technology 86
because of the low investment costs. Lithium ion batteries are

generally better in efficiency and in the number of cycles, but they

have much higher investment costs. NaNiCl batteries are also an
option for this application, but they need daily cycling to avoid
additional heating.
Smoothing out for wind (and PV) energy (MWh class)

The Japan Wind Development Co. Ltd. Has constructed a wind
power generation facility equipped with a battery in Aomori, Japan
(Futamata wind power plant, shown in Figures 8 and 9). This
facility consists of 51 MW of wind turbines (1 500 kW x 34 units)
and 34 MW of NaS batteries (2 000 kW x 17 units). By using the
NaS battery, the total power output of this facility is smoothed and
peak output is controlled to be no greater than 40 MW. Operation
started in June 2008
Fig4.3.8 General view of the Futamata wind power plant
87

Figure4.3.9. NaS battery units – 34 MW
Figure4.3.10. Example operational results of constant output control over 8 hours
Figure 10 shows an example of output from this facility. The

electric power sales plan is predetermined one day before. In order
to achieve this plan, the NaS battery system controls charging or
discharging in accordance with the output of wind power
generation. This facility meets the technical requirements of the
local utility company to connect to the grid.
88

4.3.8Management and control hierarchy of

storage systems
In this section the concepts of the management and control of

storage systems are introduced. While it is essential to have local
management for the safe and reliable operation of the storage
facilities, it is equally important to have a coordinated control with
other components in the grid when grid-wide applications are
desired. Many storage systems are connected to the grid via power
electronics components, including the converter which modulates
the waveforms of current and voltage to a level that can be fed into
or taken from the grid directly. Sometimes the converter is
connected to a transformer before the grid connection in order to
provide the required voltage. The converter is managed by a
controller which defines the set-points of the storage system. These
set-points can be expressed as the magnitude of active and reactive
power, P and Q. Such a controller may also be called control
electronics – a controller in this context is simply a representation
of the place where intelligence for decision-making is applied.
4.3.8.1Internal configuration of battery storage systems

Complex storage systems consisting of batteries are equipped with
a Battery Management System (BMS) which monitors and controls
the charge and discharge processes of the cells or modules of the
batteries. This is necessary in order to safeguard the lifetime and
ensure safe operation of the batteries. The diagram in Figure 11
shows a possible realization of the internal control architecture for a
battery storage system. It should be noted that for bulk energy
storage it is very likely that there is a more refined hierarchy for the
BMS, which involves a master control module coordinating the
charging and discharging of the slave control modules. It is possible
that the batteries and converters are from two different
manufacturers, and therefore compatibility and interoperability of 89
the two systems regarding both communication and electrical
connections is imperative.

Fig4.3.11. A possible realization of internal control architecture for a battery storage

system
4.3.8.2External connection of EES systems
The P and Q set-points for an EES for a certain application can be

set locally or remotely, depending on the control scheme
implemented. The control scheme should in turn be determined by
the application. More precisely, the application determines the
algorithmic and input/output requirements for the EES system. For
instance, an application which requires simple logic using only
local measurements can have the set-points determined locally
through the storage controller. An example of such an application is
load leveling, which only needs to know the loading conditions of
the local equipment (e.g. lines, transformers) next to which the EES
is installed. The same applies for applications which have
predetermined set-points that do not change during operation.
However, set-points for applications which require dynamic
adaptation to the network operational environment and much
remote data or measurements might be better determined by a
remote controller which can gather these remote inputs more
efficiently. One example of such an application is wind power
smoothing, which uses wind output forecasts as well as
measurements from the wind farm as inputs. Another example is 90
energy time-shifting, making use of dynamic market prices. A

generalized setup with remotely determined set-points is shown in

Figure 12. Batteries and the BMS are replaced by the “Energy
Storage Medium”, to represent any storage technologies including
the necessary energy conversion subsystem.
Fig4.3.12 A Control hierarchy involving remote data/measurements
For our project we will use the lead-acid battery and online energy
storage system configuration.
Lead-acid battery
Lead acid batteries are the world’s most widely used battery type
and have been commercially deployed since about 1890. Lead acid
battery systems are used in both mobile and stationary applications.
Their typical applications are emergency power supply systems,
stand-alone systems with PV, battery systems for mitigation of
output fluctuations from wind power and as starter batteries in
vehicles. Stationary lead acid batteries have to meet far higher 91
product quality standards than starter batteries. Typical service life
is 6 to 15 years with a cycle life of 1 500 cycles at 80 % depth of
discharge, and they achieve cycle efficiency levels of around 80 %

to 90 %. Lead acid batteries offer a mature and well-researched
technology at low cost. There are many types of lead acid batteries
available, e.g. vented and sealed housing versions (called valve-
regulated lead acid batteries, VRLA). Costs for stationary batteries
are currently far higher than for starter batteries. Mass production
of lead acid batteries for stationary systems may lead to a price
reduction. One disadvantage of lead acid batteries is usable
capacity decrease when high power is discharged. For example, if a
battery is discharged in one hour, only about 50 % to 70 % of the
rated capacity is available. Other drawbacks are lower energy
density and the use of lead, a hazardous material prohibited or
restricted in various jurisdictions. Advantages are a favorable
cost/performance ratio, easy recyclability and a simple charging
technology.
92

Transformer
Chapter 5
IN THIS CHAPTER:
 What is a transformer?
 Types of transformers
 Main Parts of Distribution

Transformers
 The regulation of a transformer
 The efficiency of a transformer
 Methods of cooling
Transformer Chapter5
5.1Introduction
The transformer is defined as a static device which by
electromagnetic induction transforms alternating voltage and
current between two or more windings at the same frequency and
usually at different values of voltage and current. The transformer
consists of two winding and iron core; the winding connected to the
source is called the primary winding, and the one connected to the
load is called the secondary winding. The two windings are
insulated from each other and from the core; the core is high
presence magnetic circuit that links all the transformer’s windings.
Energy is transferred from the primary to the secondary through a
magnetic induction. There may be more than one secondary
windings, each connected to a different load or interconnected to
provide different output voltages. Without high transmission and
distribution voltages the power losses and voltage drops associated
with line resistance would make electrical power transfer very
inefficient. Currently the highest practical generating voltage is
around 25 kV, so transformers are needed to step up voltage for
economical transmission, and step down voltage to levels that safe
for the customer to use.
 Long distance transmission is done at 132 kV, 220 kV and 500

kV ac.
 Distribution is done at 66 kV, 33 kV, 11 kV, 6.6 kV and 3.3 kV
ac.
 Utilization is done at various voltages from 11 kV to 380 volts.
Thus the electric power system has several voltage levels.
The transformer denoted by

 K.V.A. rating.
 Primary to secondary voltage and frequency.
 Winding connection (∆ or Y).
 Percentage regulation. 96

5.2 What is a transformer?

A "transformer" changes one voltage to another. This attribute is
useful in many ways. A transformer doesn't change power levels. If
you put 100 Watts into a transformer, 100 Watts come out the other
end. [Actually, there are minor losses in the transformer because
nothing in the real world is 100% perfect. But transformers come
pretty darn close; perhaps 95% efficient.
A transformer is made from two coils of wire close to each other

(sometimes wrapped around an iron or ferrite "core"). Power is fed
into one coil (the "primary"), which creates a magnetic field. The
magnetic field causes current to flow in the other coil (the
"secondary"). Note that this doesn't work for direct current (DC):
the incoming voltage needs to change over time - alternating current
(AC) or pulsed DC.
The number of times the wires are wrapped around the core
("turns") is very important and determines how the transformer
changes the voltage.
 If the primary has fewer turns than the secondary, you have a
step-up transformer that increases the voltage.
 If the primary has more turns than the secondary, you have a
step-down transformer that reduces the voltage.
 If the primary has the same number of turns as the secondary, the
outgoing voltage will be the same as what comes in. This is the case
for an isolation transformer.
Fig. (5-1) simple structure of transformer 97

5.3 Types of transformers

In general, transformers are used for power supplies. power
transformers are used to convert from one voltage to another, at
significant power levels.
5.3.1 Step-up transformers

A "step-up transformer" allows a device that requires a high voltage
power supply to operate from a lower voltage source. The
transformer takes in the low voltage at a high current and puts out
the high voltage at a low current.
5.3.2Step-down transformers
A "step-down transformer" allows a device that requires a low

voltage power supply to operate from a higher voltage. The
transformer takes in the high voltage at a low current and puts out a
low voltage at a high current.
5.3.3 Isolation transformers

An "isolation transformer" does not raise or lower a voltage;
whatever voltage comes in is what goes out. An isolation
transformer prevents current from flowing directly from one side to
the other. This usually serves as a safety device to prevent
electrocution.
5.3.4Variable auto-transformers
A "variable auto-transformer" (variac) can act like a step-up

transformer or step-down transformer. It allows you to dial in
whatever output voltage you want.
5.4Main Parts of Distribution Transformers

5.4.1Iron Core
Made of cold rolled silicon steel sheets 98

0.3mm to minimize losses

5.4.2Windings
5.4.2.1 High Voltage Windings
High tension turns are made of copper wires of either circular cross
sections varnish isolated or rectangular cross sections isolated by
silicone paper.
5.4.2.2 Low Voltage Windings
Low tension turns are made of either no insulated copper foils with
insulating paper in between or of rectangular wires insulated by
cylindrical paper sheets.
5.4.3Tank
The transformer tank is made of corrugated steel, the corrugated

tank surface is itself the cooling surface, the tank is provided with
an additional steel reservoir for oil expansion, on which a piping
device is installed to transmit oil cock, a hole for silica gel
apparatus and an oil level indicator.
5.4.4Oil Expansion Conservator

5.4.5 Terminals
(High voltage)H.V.and (Low voltage)L.V. terminals are brought

out through porcelain bushings according to the rated voltage. The
insulators are fixed to the tank cover in such a way to ensure
replacement without dismantling the transformer cover. Cable end
boxes on either H.T. or L.T. side or both can be made if required.
5.4.6 Tap Changer
Tap changers are externally for allowing voltage regulation with ±5

% of the rated value in 5 equal steps of ± 2.5 % each, the tap
changer is manually operated while current is off.
5.4.7Cooling Oil
Transformers are filled with special oil (Duala (5) or equal) of high
insulating grade according to IEC 99
specifications.

5.5Number ofphases
5.5.1Single phase.
Two or more winding, coupled by acommon magnetic core.
5.5.2Poly phase.
A polyphase transformer
consists of separate insulated
electric windings for the
different phases, wound upon a
single core structure, certain
portions of which are common
to the different phases as shown
in figure (5.10)
Fig (5.2)
5.6Transformer ratios
The voltage ratio of a constant-voltage transformer, i.e., the ratio of
primary to secondary voltage, depends primarily upon the ratio of
the primary to the secondary turns. The voltage ratio will vary
slightly with the amount and power factor of the load. For general
work the voltage ratio can be taken as equal to the turn ratio of the
windings. The current ratio of a constant-voltage transformer will
be approximately equal to the inverse ratio of the turns in the two
windings.
5.7The regulation of a transformer

The change in secondary voltage from no load to full load, It is
generally expressed as a percentage of the full-load secondary
voltage.
100

5.8The efficiency of a transformer

The ratio of the out-put to input or, in other words, the ratio of the
output to the output plus the losses, As a formula it can be
expressed thus
5.9Parallel operation of the transformers

Some factories need a parallel operation of two or more power
transformers, the essential requirements for this parallel operation
are:
1. The polarity should be the same.

2. The voltage ratio should be the same.
3. The percentage impedance should be equal.
4. The phase rotation should be the same.
5. The vector diagrams and the phase displacement should be the
same.
If the voltage ratio not the same, for the same primary voltage the
secondary voltages will be different between the transformers
which causes a circulating current within the secondary circuit and
heating the transformer even on no load.
Also, to operate two transformers in parallel operation they must

have the same percentage impedance to make the loading of them
proportional to their kVA rating as percentage.
101

Fig (5.3) shows the the correct connection and the wrong connection of transformers used in
parallel operation.
5.10Methods of cooling
High temperatures will damage the winding insulation. Power
transformers rated up to several hundred kVA can be adequately
cooled by natural convective air-cooling, sometimes assisted by
fans. In larger transformers, part of the design problem is removal
of heat. Some power transformers are immersed in transformer oil
that both cools and insulates the windings. Some "dry" transformers
(containing no liquid) are enclosed in sealed, pressurized tanks and
cooled by nitrogen or sulfur hexafluoride gas.
5.10.1Oil-Immersed Distribution Transformer
This kind of product is applied for power system of three-phase,

50Hz as well as 35kV and below. It is the main transformer
equipment of medium and small-sized transformer substation;
Supplies power distribution, power and illumination for the industry
and agriculture. The company introduces advanced technique,
adopts the latest material and optimized design, which enables the
product structure more reasonable, and greatly improves the
product electric strength, mechanical strength and heat-sinking
capability.
Fig. (5-2) Oil-Immersed Distribution Transformer
102

5.1.0.2Dry-type transformer
Dry type transformers require minimum maintenance to provide

many years of reliable trouble free service. Unlike liquid fill
transformers which are cooled with oil or fire resistant liquid
dielectric, dry type units utilize only environmentally safe. Dry type
transformers provide a safe and reliable power source which does
not require fire proof vaults, catch basins or the venting of toxic
gasses. These important safety factors allow the installation of dry
type transformers inside buildings
Close to the load which improves over all system regulation and
reduces costly secondary line losses.
Dry type transformer are a rather mature product and technology

but, of all the components in a power system, a transformer
replacement can be a physically challenging event, extended
delivery of a replacement or repair unit and expensive
transportation costs. These are transformers whose core and coils
are not immersed in an insulating oil.
“Dry type” simply means it is cooled by normal air ventilation. The

dry type transformer does not require a liquid such as oil or silicone
or any other liquid to cool the electrical core and coils.
Due to the previous advantages of dry-type transformer it’s more

suitable for this project and we will put it in the basement.
5.11 Specification of the used transformer

The many uses to which transformers are put leads them to be
classified in a number of different ways [3] :
Transformer 1 MVA: 3-phase, 50 Hz
∆-Y connection
103
Step-down 22/0.4 KV
Z%=5%
No load power = 1.22 KW
Transformer 1.5 MVA: 3-phase, 50 Hz
∆-Y connection
Step-down 22/0.4 KV
Z%=6%
No load power = 1.78 KW
5.12Determining capacity of thetransformer

Stating transformer capacity according to electrical loads expected
for the construction 80% of it’s capacity.
By summing the total loads of each block, the transformer capacity

ratings are determined as shown in table (5-1).
ZONES blocks ratings
ZONE1 Block1+block7+m 2.5

all+office(block2) MVA
ZONE2 Block3+block6+ho 2.5
tel MVA
(block2)
ZONE3 Block4+block5 2.5
MVA
104

105

Cables
IN THIS CHAPTER:
Chapter 6
 Cable insulation materials
 Derating Factors
 Calculation of cross section of

cables
 voltage drop calculation
 Distribution panels
Cables Chapter6
6.1 Introduction
This Chapter is concerned with the selection of wiring cables for use
in an electrical installation. It also deals with the methods of
supporting such cables, ways in which they can be enclosed to provide
additional protection, and how the conductors are identified. All such
cables must conform in all respects with the Egyptian Code (E.C).
This Electrician's Guide does not deal with cables for use in supply
systems, heating cables, or cables for use in the high voltage circuits
of signs and special discharge lamps.
6.2 Factors considered in design and selection

of cables
The following factors are important when selecting a suitable cable
construction which is required to transport electrical energy from the
power station to consumer:
 Maximum operating voltage.
 Insulation level.
 Frequency.
 Load to be carried.
 Magnitude and duration of possible overload.
 Magnitude and duration of short-circuit current.
 Voltage drop.
 Length of line.
 Mode of installation.
 Underground (direct or in ducts).
 In air.
 Chemical and physical properties of soil .
 Max and min. ambient air temperatures and soil temperature.
107
 Specification and requirements to be met.

Cables Chapter6
6.3 Cable insulation materials

6.3.1 Paper
Dry paper is an excellent insulator but loses its insulating properties
if it becomes wet. Dry paper is hygroscopic, that is, it absorbs
moisture from the air. It must be sealed to ensure that there is no
contact with the air. Because of this, paper insulated cables are
sheathed with impervious materials, lead being the most common.
PILC (paper insulated lead covered) is traditionally used for heavy
power work. The paper insulation is impregnated with oil or non-
draining compound to improve its long-term performance. Cables of
this kind need special jointing methods to ensure that the insulation
remains sealed. This difficulty, as well as the weight of the cable, has
led to the widespread use of p.v.c. and XLPE (thermosetting)
insulated cables in place of paper insulated types.
6.3.2 P.V.C.
Polyvinyl chloride (p.v.c.) is now the most usual low voltage cable
insulation. It is clean to handle and is reasonably resistant to oils and
other chemicals. When p.v.c. burns, it emits dense smoke and
corrosive hydrogen chloride gas. The physical characteristics of the
material change with temperature: when cold it becomes hard and
difficult to strip, and so BS 7671 specifies that it should not be worked
at temperatures below 5°C. However a special p.v.c. is available
which remains flexible at temperatures down to -20°C.
6.3.3 Thermosetting (XLPE)

Gross-linked polyethylene (XLPE) is a thermosetting compound
which has better electrical properties than p.v.c. and is therefore used
for medium- and high-voltage applications. It has more resistance to
deformation at higher temperatures than p.v.c., which it is gradually
replacing. It is also replacing PILC in some applications.
Thermosetting insulation may be used safely with conductor
temperatures up to 90°C thus increasing the useful current rating,
especially when ambient temperature is high.
6.4 Derating Factors

The environmental and thermal conditions where a trailing cable is 108
used and the thermal resistance of its insulation determine a cable’s
ampacity rating. Cables used on reels on mobile machinery also have
a derating factor applied to account for the heating effects of having
Cables Chapter6
one or more layers consistently on the reel. The more layers on the
reel, the less amperage a cable can handle due to the effects caused by
the buildup of heat.
These following derating factors are considered in our calculation
1- Ground temperature derating factor
2- Burial depth derating factor
3- Soil thermal resistivity derating factor
4- Trefoil or flat derating factor
109

Cables Chapter6
In our calculation we used this values:

1- Ground temperature derating factor = 1 at ground temperature =
0
35 c.
2- Burial depth derating factor = 0.99 at 0.06m.
3- Soil thermal resistivity derating factor=1 at Soil thermal
resistivity=120 Ώ m.
4- Trefoil derating factor .
6.5 Calculation of cross section of cables

First we can calculate the load current from the relation :
S
I(load) 
3 V
where S : the load in KVA

V : the operating voltage in KV
I(load): load current in Amp
After that we can calculate the rating current by dividing the load
current by the total derating factor (df)
I load
I(rate) 
df
As total derating factor (df)=

Ground temperature derating factor* Burial depth derating factor*
Soil thermal resistivity derating factor* Trefoil derating factor.
With the result of rating current we can calculate the cross section area
of cable by using (2).
110

Cables Chapter6
6.5.1Cables selected in our project :

6.5.1.1 Medium voltage cable:
111

Cables Chapter6
6.5.1.2 Low voltage cable:
112

Cables Chapter6
113

Cables Chapter6
6.6 voltage drop calculation

Voltage drop (V.D) at each circuit could be calculated by formula
voltage drop per meter length (v/m) as referred to table (5-1) and the
current value passing through the cable can be calculated by the
equation:
A
V .D  mV  L   100
n
Where:
mV: V.D per meter per ampere.
L : cable length.
A : current value.
n : number of cables per phase.
The value of V.D related to the type of cable and its cross section
per meter length can be given from factory's manuals [2]
The length of cable is measured between the main switch board and
the sub main switch board. The distance between boards, the spear
length and non-linear distance must be taken in consideration to
determine cable length.
- The allowable percentage value of voltage drop is 5%
5
 400  20volt
100
- Any value more than 20 volt, voltage drop is rejected.

- If the voltages drop percentage more than 5%, the cable cross section
must be maximized to eliminate voltage drop.
For example
- We will take the voltage drop calculation of block (1).
6.5.1 Street lights cable:

34
V .D  5.199  50 
1000
=8.8 volt < 20 acceptable 114

Cables Chapter6
6.5.2 Ground cable:

74
V .D  1.280  40 
1000
=3.7 volt < 20 acceptable
6.5.3 Building (10C)
297.33
V .D  0.18  50 
1000
=2.6volt < 20 acceptable
6.5.4 Building (5)
111.13
V .D  0.72  20 
1000
6.5.5 Building (13A)
326.32
V .D  0.157  150 
1000
6.5.6 Building (13B)
353.77
V .D  .18  110 
1000
=7 volt <20 acceptable
115

Cables Chapter6
Table (6.1) voltage drop calculation
116

Cables Chapter6
6.6 Joints and terminations:

The normal installation has many joints, and it follows that these
must all remain safe and effective throughout the life of the system.
With this in mind, regulations on joints include the following:
1. All joints must be durable, adequate for their purpose, and
mechanically strong.
2. Where sheathed cables are used; the sheath must be continuous into
the joint enclosure
Fig (6.1) The joint between two cables
Fig(6.2)cable-termination
117

Cables Chapter6
6.7 Cable trays:

Is Stephens Metal Plates fixed in the walls hinged on roofs to put the
cables in it and it used in case of a lot of feeders for installation as
shown in fig (6.3 a&b)
(a) (b)
Fig (6.3) Cable trays
6.7.1 Types of cable trays:

It may be metallic or non metallic made of suitable substance.
6.7.1.1 Ladder
Made of steel as tow plates connected together . These trays offer
strength and high capacity in industrial facilities. Also it is good in
case of heavy loads of cables as ( power station – cement factory –
heavy industries – chemical industries ) and it gives the best solution
for towers and high building. Fig (6.4)
6.7.1.2 Cable Tray (Race Ways):

* Features:
- Highly durable
- Excellent finishing
- Resistance to corrosion
- High performance 118
- Cost effective etc.

Cables Chapter6
* Application:
Widely used in glass, electronic, photo voltaic and automotive
industry. Fig(6-5).
Fig(6-4) Ladder type fig(6-5) Race Ways
6.8 The Conduits :

The electrical color to distinguish conduits from pipelines of other
services is orange as shown in fig (6-6 )
119
Fig(6.6) The Conduits

Cables Chapter6
6-9 Cable Trench / Channel :

Trench is an ideal, accessible runway for power cables /
distribution , control and communication wiring , industrial piping ,
and Telecommunication wires.
It is suitable to choose the best under ground installation cables far
from the lines of water, gases and telephone, choose the places at
intersections with streets, and put the best conduits for cables cross
sections.
For the under voltage the cutting section will be 400 cm wide and 80
cm depth for the single cable and 100 cm in case of the medium
voltage and the wide increases with a space of 20cm in for any
additional cable.
At the bed cutting it put layer of sand with a depth of 10 cm and over
the cable . It put layer of sand with a depth of 20 cm .
Layer of Brick put then smooth fill put after that alarm tape put at the
depth of 30 cm . as shown in fig (6-7)..
Fig( 6-7)
Benefits of Cable Trench

1)Handling easy . 120
2)Installation is simple as shown in fig(6-8)

3)Substation expansion
Cables Chapter6
Fig(6-8) Installation of Cable Trench
Cable trench layout is indicated as shown in fig(6-9)
121

Cables Chapter6
Fig(6-10) Cable Trench / Channel layout
4-10 Distribution panels:

A single panel or group of panels units designed for assembly in the
form of a single panel placed after the incoming feeders from
transformer including buses, automatic over current devices, and
equipped with or without switches for the control of light, heat, or
power circuits; designed to be placed in a cabinet or cutout box placed
in or against a wall or partition and accessible only from the front .
122

Cables Chapter6
6.10.1 Medium voltage distribution panel (M.V.D.P) :
Fig 6-11 components of (M.V.D.P)
6.10.1.1 Measuring instruments:
a) At incoming panel:
-Voltmeter and voltage transformer (V.T).

-Three ammeter and current transformer (C.T).
-Wattmeter feds from (V.T , C.T).
-VAR meter feds from (V.T , C.T).
-Power factor (P.F) meter feds from (V.T , C.T).
-Watt hour meter feds from (V.T , C.T).
-VAR hour meter feds from (V.T , C.T). 123
-Frequency meter (Hz).

Cables Chapter6
b) At outgoing panel:
-Three ammeter and (C.T).

-Watt hour meter (Wh).
-VAR hour meter (VARh).
c) at bus-tie panel:
- Three ammeter and current transformer (C.T).
6.10.1.2 Protection instruments:
a) At outgoing feeders:
- Non directional over current protection relay feds from (C.T, D.C).
- Non directional earth fault current protection feds from (C.T , D.C).
-D.C source .
b) At incoming circuits:
-Non directional over current protection relay fed from (C.T, D.C).
- Non directional earth fault current protection relay fed from (C.T ,
D.C).
-D.C source.
c) At BUS-Tie panel:
-Non directional over current protection relay feds from (C.T, D.C).
- Non directional earth fault current protection relay fed from (C.T ,
D.C).
-Earth leakage E/L relay.
-Three ammeter and current transformer (C.T).
-D.C source .
6.10.1.3 switchgears instruments:
In all panel ( incoming , outgoing and bus-tie or bus-coupler) there

are:
- circuit breaker
-Earth switch.
-Load break switch. 124

Cables Chapter6
6.10.2 Low voltage distribution panel
Distribution boards is a panel used to distribution inside the floors

which is divided to two main types
6.10.2.1Main panel
Main panel provide protection

against over current fault and
short circuit fault which can be
controlled by the rating selection
of breakers and short circuit level
which it’s depend on the load
rating and board distance from
supply.
The components:
a) Fuse
b) Circuit breaker
Types of circuit breaker
a) Miniture circuit breaker

b) Moulded case circuit breaker
125

Cables Chapter6
6.10.2.2 Sub panels
The sub panel is panels which it’s distributed inside the floor and
it’s number depend on the floor geometry and floor loads (sockets,
lighting, appliance ).
the sub panel is nearly look like the main floor panel in construction
it’s consist of main breaker 3 Ø and sub breakers 1Ø which feeds
directly to the loads through wires to the loads.
126

Earthing
IN THIS CHAPTER:
Chapter 7
 Advantages& Disadvantages of
Earthing
 Combining neutral with earth
 IEC Terminology
 Theory vs. practice
 Soil Resistivity
Earthing Chapter 7
7.1 Introduction
Ground or earth in a mains (AC power ) electrical wiring
system is a conductor that exists primarily to provide a low
impedance path to the earth to prevent transient hazardous voltages
from appearing on equipment ; normally a grounding conductor
does not carry current . Neutral is a circuit conductor that may carry
current in normal operation, and which is usually connected to
earth.
In shortly the grounding or earting is done for safety purposes to

protect people from the effects of faulty insulation on electrically
powered equipment. A connection to ground helps limit the voltage
built up between power circuits and the earth, protecting circuit
insulation from damage due to excessive voltage. Connections to
ground may be used to limit the build-up of static electricity when
handling flammable products or when repairing electronic devices.
In some types of telegraph and power transmission circuits, the
earth itself can be used as one conductor of the circuit, saving the
cost of installing a separate run of wire as a return conductor. For
measurement purposes, the Earth serves as a (reasonably) constant
potential reference against which other potentials can be measured.
An electrical ground system should have an appropriate current-
carrying capability in order to serve as an adequate zero-voltage
reference level. In electronic circuit theory, a ground is usually
idealized as an infinite source or sinks for charge, which can absorb
an unlimited amount of current without changing its potential.
7.2 The advantages of Earthing

The practice of earthing is widespread, but not all
countries in the world use it. There is certainly a high cost
involved, so there must be some advantages. In fact there are two.
They are:
1- The whole electrical system is tied to the potential of the general
mass of earth and cannot float at another potential. For example, we
128
can fairly certain that the neutral of our supply is at, or near, zero
volts (earth potential) and that the phase conductors of our standard

Earthing Chapter 7
supply differ from earth by 240 volts.

2- By connecting earth to metalwork not intended to carry current
(an extraneous conductive part or a an exposed conductive part ) by
using a protective conductor, a path is provided for fault current
which can be detected and , if necessary, broken . The path for this
fault current is shown in (Fig 7-1).
Fig 7-1 path for earth fault current (shown by arrows)
7.3 The disadvantages of Earthing

7.3.1 The two important disadvantages are :
1- Cost: the provision of a complete system of protective
conductors, earth electrodes, etc. is very expensive.
2- possible safety hazard: It has been argued that complete
isolation from earth will prevent shock due to indirect contact
because there is no path for the shock current to return to the
circuit if the supply earth connection is not made (see [Fig 7-2(a)])
.This approach, however, ignores the presence of earth leakage
resistance (due to imperfect insulation) and phase -to- earth
capacitance (the insulation behaves as a dielectric). In many
129
situations the combined impedance due to insulation resistance

Earthing Chapter 7
and earth capacitive reactance is low enough to allow a significant

shock current (see [Fig 7-2(b)] ) .
Fig 6.2 Danger in an unearthed system
A. Apparent safety: no obvious path for shock current.

b. Actual danger: shock current via stray resistance and capacitance.
7.4 Combining neutral with earth

Connecting the neutral to the equipment case provides some
protection against faults / shorts, but may produce a dangerous
voltage on the case if the neutral connection is broken.
Combined neutral and ground conductors are commonly used in

electricity supply companies wiring and occasionally for fixed
wiring in buildings and for some specialist applications where there
is little choice like railways and trams. Since normal circuit currents
in the neutral conductor can lead to objectionable or dangerous
differences between local earth potential and the neutral and to
protect against neutral breakages, special precautions such as
frequent rodding down to earth, use of cables where the combined
neutral and earth completely surrounds the phase conductor(s), and
thicker than normal equipotential bonding must be considered to
ensure the system is safe.
7.5 In household wiring

There are two main approaches to the problem of how to 130
disconnect power when a live wire comes into contact with
metalwork attached to the earthing system: One way is to get the
Earthing Chapter 7
resistance through the fault path and back to the supply very low by
having a metallic connection from the earth back to the supply
transformer (a TN system). Then when a fault happens a very high
current will flow rapidly blowing a fuse (or tripping a circuit
breaker).
The second approach, where such a direct connection is not used

(a TT system) , the resistance of the fault path back to the supply is
too high for the branch circuit over current protection to operate
(blow a fuse or trip a circuit breaker) . In such case a residual
current detector is installed to detect the current leaking to ground
and interrupt the circuit.
7.6 IEC Terminology

International standard IEC 60364 distinguishes three families of
earthing arrangements, using the two - letter codes TN, TT, and IT.
The first letter indicates the connection between earth and the
power - supply equipment (generator or transformer):
T: direct connection of a point with earth (French: terre);
I: no point is connected with earth (isolation) , except perhaps via a
high impedance .
The second letter indicates the connection between earth and the
electrical device being supplied:
T: direct connection with earth, independent of any other earth
connection the supply system.
N: connection to earth via the supply network.
The third and fourth letters indicate the arrangement of the earthed
supply conductor system.
S: neutral and earth conductor systems are quite separate.

C: neutral and earth are combined into a single conductor.
7.6.1 TN network
In a TN earthing system, one of the points in the generator or 131
transformer is connected with earth, usually the star point in the

Earthing Chapter 7
three-phase system. The body of the electrical device is connected

with earth via this earth connection at the transformer.
The conductor that connects the exposed metallic parts of the

consumer is called protective earth (PE). The conductor that
connects to the star point in a three-phase system , or that carries the
return current in a single - phase system , is called neutral (N) .
Three variants of TN systems are distinguished: TN-S: PE and N
are separate conductors that are connected together only near the
power source.
TN-C: A combined PEN conductor fulfills the functions of both a
PE and an N conductor.
TN-C-S: Part of the system uses a combined PEN conductor,
which is at some point split up into separate PE and N lines. The
combined PEN conductor typically occurs between the substation
and the entry point into the building; where as within the building
separate PE and N conductors are used. In the UK , this system is
also known as protective multiple earthing (PME) , because of the
practice of connecting the combined neutral - and - earth conductor
to real earth at many locations , to reduce the risk of broken neutrals
- with a similar system in Australia being designated as multiple
earthed neutral (MEN) .
TN-S: separate protective earth
(PE) and neutral (N) conductors
from transformer to consuming
device, which are not connected
together at any point after the 132
building distribution point .

Earthing Chapter 7
TN-C: combined PE and N

conductor all the way from the
transformer to the consuming device.
TN-C-S earthing system:

combined PEN conductor from
transformer to building distribution
point, but separate PE and N
conductors in fixed indoor wiring and
flexible power cords.
It is possible to have both TN-S and TN-C-S supplies from the

same transformer. For example, the sheaths on some underground
cables corrode and stop providing good earth connections, and so
homes where “bad earths " are found get converted to TN-C-S .
7.6.2 TT network
In a TT earthing system, the protective earth connection of the
consumer is provided by a local connection to earth, independent of
any earth connection at the generator.
133

Earthing Chapter 7
6.6.3 IT network
In an IT network, the distribution system has no connection to
earth at all, or it has only a high impedance connection. In such
systems, an insulation monitoring device is used to monitor the
impedance.
7.7 Theory vs. practice

Theoretically, the resistance to remote earth of an earth electrode
can be calculated. This calculation is based on the general 134
resistance formula:
R = (r × L)/ A

Earthing Chapter 7
where:
R: resistance to remote earth (W)
r: soil resistivity (W-cm)
L: length of conducting path (cm)
A: cross-sectional area of path (cm)
This general fomula is a simplified version of some complex

formulas ( derived by professor H. B. Dwight of Massachusetts
Institute of Technology ) used to calculate the resistance to remote
earth for a grounding system . The assumption in the general
formula is that the resistivity of the soil is constant throughout the
considered area , or averaged for the local soil . In the practical
(real) world , soil resistivity is not constant , properties of electrodes
and thier connections vary ( except with CADWELDTM ) , and
complex equations just don't cut it . Therefore , an actual measuring
technique is necessary . This technique is done with an earth
resistance tester . One example of the earth tester is the ERICO
EST301 Universal Earth System Tester , seen in figure 6-3 ,(please
refer to the ERICO EST301 Operating Instructions manual for
detailed instructions on its use . ) This type of instrument can be
used at various stages in the life of a grounding system , once
during installation to see if it meets all specifications , and anytime
there after to observe any possible changes.
Figure 7.3: ERICO EST301 Universal Earth system Tester
7.8 Earth Electrode Measurement (single

Electrode)
There exist different measuring techniques for resistance to remote
135
earth of a grounding system. One such technique is the 3-pole earth
electrode measurement for a single electrode. This technique uses

Earthing Chapter 7
the electrode under test (EUT), a reference probe, and an auxiliary

probe, set in a straight line. Figure 6-4 shows the single electrode
measuring method, and figure 6-5 shows the single electrode
measuring setup for the ERICO EST301 earth tester.
Figure 6.4: Single Electrode Measuring Method
Figure 6-5: Single Electrode Measurement Setup
After applying a voltage at the designated location in the circuit,

the current between the EUT and the auxiliary probe is measured,
and the voltage between the EUT and the reference probe is
measured. Using Ohm's Law, the resistance can now be calculated.
This routine is completed by the earth tester. It has been determined
that the distance D be approximately 100 feet , and the distance
between the EUT and reference probe be 0.62 times the value of D .
These values have been tested using the fall of potential method to
give optimal results (see figure 6-6). But due to the large amounts
of uncertainty in all properties of probes and soil, the value of D 136
should be varied for each individual test until reasonably consistent
values appear; however, it is recommended that the value of D stay
Earthing Chapter 7
greater than 80 feet. It is also necessary to take a second set of

readings at 90 to the original in case of interference from overhead
power lines or any underground electrical equipment or metal
objects.
Figure 6.6: Fall of Potential
7.9 Earth Electrode Measurement (Multiple

Probe System)
A second earthing resistance measuring technique is the process
of measuring the resistance to remote earth of a single earth
electrode in a multiple electrode grounding system. This technique
is used when the earth electrode cannot be disconnected from the
rest of the grounding system such as a communication tower
installation. When the earth electrode can be disconnected, the
previous 3-pole single electrode technique may be used. Caution
should always be taken when disconnecting any earth electrode.
The same principles apply to this technique as they did for the
single probe technique; the only difference is that for the multiple
electrodes grounding system, the current is measured with a current
transformer around the EUT, (see figures 6-7 and 6-8.) After the
proper voltage and current values are measured, a simple Ohm's
Law equation determines the electrode's resistance to remote earth.
137

Earthing Chapter 7
Figure 6.7: Multiple Electrodes Measuring Method
Figure 6.8: Multiple Electrode Measurement Setup
Once the resistance to remote earth for each electrode in the entire
grounding system is determined, one can calculate the resistance to
remote earth for the entire grounding system in one of two ways. The
first approach is in understanding that the electrodes are in parallel
with each other (through the grounding grid and ground itself.)
Because they are in parallel, the rule for parallel resistances can be
used.
Rs=1/ [ (1/R1) + (1/R2) + (1/R3) + .....(1/Rn)]

Where:
Rs : resistance to remote earth for entire grounding
system (W)
R1,2,3...n : resistance to remote earth for each
individual electrode (W)
However, this rule is not completely accurate in this application

138
because of the extra resistance to remote earth through the
grounding grid. The second approach used to calculate the

Earthing Chapter 7
resistance to remote earth for the entire grounding system assumes

that the resistances to remote earth for earth electrode are equal.
Then , for the entire grounding system , the resistance to remote
earth is 40 % lower for a system with only two electrodes , 60 %
lower for a system with three electrodes , and 66% lower for a
system with four electrodes ( compared to the resistance to remote
earth for one of the equal electrodes .) These values are slightly
larger than the values given by the parallel resistance rule.
7.10 Soil Resistivity
The second major factor in determining how well a grounding
system performs is the resistivity of the local soil. Soil resistivity is
the resistance measured between two opposing surfaces of a 1 m3
cube of homogeneous soil material (see figure 6-9,) usually
measured in Ω-m, or Ω-cm. Soil resistivity has a direct effect on the
resistance of the grounding system . The evaluation of the
resistivity of the local soil can determine the best location, depth,
and size of the electrodes in a grounding system, and can also be
used for many other applications. A geological survey uses the soil
resistivity to locate ore, clay, gravel, etc. . . . Beneath the earth's
surface. Depth and thickness of bedrock can also be determined.
The degree of corrosion of the local soil also can be obtained from
its resistivity value. Due to these many reasons, it is necessary to
measure the resistivity of the local soil.
Figure 7.9 : Soil Resistivity Definition Cube
Many different factors have a direct effect on the resistivity of the

local soil. A large factor is the type of soil. The resistivity range can
go from 1 W-cm to the upwards of over 1,000,000 W-cm (see
figure 6-10.) Moisture content can be a large factor in determining 139
the resistivity of the local soil. The drier the soil, the higher the

Earthing Chapter 7
resistivity. remains relatively low (and constant ) if the moisture

content of the soil is greater than 15 % ( by weight ,) and skyrockets
for lower values of moisture content . Another large factor in the
determination of soil resistivity is the content of minerals, such as
salts or other chemicals. For values of 1 % (by weight) salt content,
the soil resistivity remains low (and constant,) and skyrockets for
lower values of salt content. Finally, compactness and temperature
can set the resistivity of the local soil. With temperature, the colder
the soil is, the higher the resistivity. Due to seasonal changes where
the local soil can also change drastically (see figure 6-11.) Many of
these factors (moisture content, mineral content, compactness, and
temperature,) of the local soil can change during the life of the
grounding system, and therefore change the resistance to remote
earth of that grounding system.
Figure 7.10: Resistivity range for different types of soil
Figure 7.11: Typical electrode resistance to remote earth in a year

140
Like the resistance to remote earth of an electrode, measuring the
resistivity of the local soil can be done with a specific metering

Earthing Chapter 7
device. The process is sometimes referred to as the four pole (or

four - terminal) method (see figures 7-12 and 7-13.)
Figure 7.12: Soil Resistivity -Four Pole Method
Figure 7.13: Soil Resistivity - Four Pole Setup
Four small electrodes (auxiliary probes) are placed in a straight line

at intervals of a, to a depth of b. A current is passed through the
outer two probes, and the potential voltage is then measured
between the two inner probes. A simple Ohm's Law equation
determines the resistance. From this information, it is now possible
to calculate the resistivity of the local soil by using the Equally
Spaced (or Wenner Arrangement) method.
r = [4×p×a×R] / [1 + ((2×a) / SQRT (a2 + 4×b2))-(a /

SQRT (a2 + b2))]
where
r = resistivity of the local soil (W-cm)
a = distance between probes (cm) 141

Earthing Chapter 7
b = depth of probes into the ground (cm)

R = resistance determined by the testing device (W)
For most practical circumstances, a is twenty times larger than

b, where we can then make the assumption that b=0, and the
formula becomes simply:
r=2×p×a×R
these values give an average resistivity of the soil to a depth of
the value of a. It is recommended that a series of readings be taken
at different values of a, as well as in a 90‫ ס‬turned axis, so that the
measuring results are not distorted by any underground pieces of
metal (pipes, ground cables, etc.) These final values should be
plotted, so that a consistent value is determined.
So in our project “Smart City project “we used the TT network to
earthing all the building and other constructer and to design our
earthing system network we must have some requirements:
Soil resistivity
Off-frequency Injection
Determination of Step & Touch Potential. Soil resistivity be
determine by making tests in soil and after that we use the result in
Grounding Design Assistant program to find the dimension of the
electrode and the dimension cables In our project we estimate the
result to design the earth electrode and network of earthing.
142

Protection System
IN THIS CHAPTER:
Chapter 8
 Circuit breaker and their types
 Types of protection used in our

project
 Calculation of short circuit current

Protection system Chapter8
8-1 Introduction
Every electrical thing need protection .The house wiring is
protected by fuse. Modern generators are protected by complex
protective schemes . Protective relays is necessary with every
electrical plant and not part of power system is left unprotected. The
choice of protection is depend upon some aspect such as type and
rating of protected equipment, its importance, location, probable
abnormal condition, cost, etc…
The need of protective relaying protects the concerned equipment
from abnormal operating condition and faults. When an abnormal
condition develops in the protected equipment or machine , the
protective relaying for the protected equipment or machine sense
the abnormal condition and initiates an alarm or closes the tripping
circuit of the circuit breaker (C.B) so as to open the C.B and isolate
the equipment or machine from the supply. In other words,
protective relaying senses the abnormal condition in apart of the
power system and gives an alarm or isolates that faulty system from
healthy system. This can be achieved by essential component that
are C.B. and relays.
It should be note that protection relay does not prevent the
appearance of faults . It can take action only after fault has
occurred. Relay distinguish between normal and abnormal
condition .Whenever an abnormal condition develops, the relay
close its contacts, there by the trip circuit of the C.B. is closed.
Current from supply flow in the trip coil of the C.B. and C.B. opens
and faulty part is disconnected from supply. Removal of faulty part
from the system is automatic and fast.
Besides the relays and C.Bs ,there are several other important
components in protective relay scheme, these include protective
current transformers, voltage transformer ,auxiliaries, etc... Each
component is important. Protective relaying is a team-work of
these components.
The function of Protective relaying include the following :
144
1. To sound an alarm or to close the trip circuit of C.B. so as to
disconnect a component during an abnormal condition in the

component, which include over-load, under-voltage, temperature

rise, short circuits, reverse power, etc...
2. To disconnect the abnormally operating part so as to prevent the
subsequent faults.
3. To localize the effect of fault by disconnecting the faulty part.
4. To disconnect the faulty part quickly so as to improve the system
stability, service continuity and system performance.
8-2 Circuit breaker

A circuit breaker is an automatically operated electrical switch
designed to protect an electrical circuit from damage caused by
overload or short circuit. Its basic function is to detect a fault
condition and interrupt current flow. Unlike a fuse, which operates
once and then must be replaced, a circuit breaker can be reset
(either manually or automatically) to resume normal operation.
Circuit breakers are made in varying sizes, from small devices that
protect an individual household appliance up to large switchgear
designed to protect high-voltage circuits feeding an entire city.
8-3 The types of the Circuit breakers

8-3-1 Medium voltage circuit breaker
The type of the Circuit Breaker is usually identified according to
the medium of arc extinction. The classification of the Circuit
Breakers based on the medium of arc extinction is as follows:
1-Oil Circuit Breaker (tank type of bulk oil)
2-Minimum oil Circuit Breaker.
3-Air blast Circuit Breaker.
4-Vacuum Circuit Breaker.
5-Sulphur hexafluoride (SF6)Circuit Breaker.
The type of CB we Used in medium voltage is Sculpture
hexafluoride (SF6) Circuit Breaker.
145
Sulphur hexafluoride (SF6)is an inert, heavy gas having good
dielectric and arc extinguish properties.SF6 is now widely used in
electrical equipment like high voltage metal encloused cables,
capacitors, C.Bs ,current transformers, etc.... This gas is

commercially manufactured in many countries. It has good physical
properties such as it is colorless, odorless, state gas at normal
temperature and density-heavy gas as its density is 5 times that of
air at 20ºC and atmospheric temperature .It is stable up to 500ºC.
The chemical inertness of gas is an advantageous in switchgear.
The life of metallic part, contact is longer in SF6 gas. Its component
does not get oxidized or deteriorated. Hence maintenance
requirements are reduced. The breaker may need maintenance once
in four to ten year.
The merits of SF6 Circuit Breaker are :
a) Excellent insulating ,arc extinguishing ,physical and
chemical properties of SF6 gas is greatest advantage of Sf6
breaker.
b) The maintenance require is minimum .The breaker may need
maintenance once is four to ten years.
c) The Sf6 breaker does not make sound like air blast C.B
during operation.
d) Contact corrosion is very small due to internees of gas.
Hence contact does not suffer oxidation.
e) Non over current problem.
8-3-2 Low voltage circuit breakers

There are many different technologies used in circuit breakers and
they do not always fall into distinct categories. Types that are common
in domestic, commercial and light industrial applications at low
voltage (less than 1000 V) include:
1. MCB (Miniature Circuit Breaker) :Its rated current not more
than 100 A.
2. MCCB (Molded Case Circuit Breaker): Its rated current up to
1000A.
8-3-2-1 Miniature circuit breaker:
M.C.B. could operate automatically at rated current of 125A
146
(single or three phase).To provided with thermal elements for
protect against short circuit .The disconnecting capacity must be
less than 6KA at 220v at P.F. between (0.5 - 0.6) lag with taken in

consideration location of circuit breaker or choosing suitable rated

for disconnection capacity.
Fig(8-1) is a photograph of the internal details of a 10 ampere
European thermal-magnetic miniature circuit breaker. Circuit
breakers such as this are the most common style in modern
domestic consumer units and commercial electrical distribution
boards throughout Europe.
Unfortunately while the size and shape of the opening in the front
and its elevation from the rail are standardized the arrangements for
bus bar connections are not so you should take care that the breaker
you select fits the bus bar in your board and preferably is the same
make and range.
Fig(8.1) is a photograph of miniature circuit breaker.
1. Actuator lever - used to manually trip and reset the circuit

breaker. Also indicates the status of the circuit breaker (On or
Off/tripped). Most breakers are designed so they can still trip even
if the lever is held or locked in the on position. This is sometimes
referred to as "free trip" or" positive trip" operation.
2. Actuator mechanism - forces the contacts together or apart.
3. Contacts - Allow current to flow when touching and break the
flow of Current when moved apart.
4. Terminals.
5. Bimetallic strip.
147
6. Calibration screw - allows the manufacturer to precisely adjust
the trip Current of the device after assembly.
7. Solenoid.
8. Arc divider / extinguisher.

8-3-2-2 Molded case circuit breaker
Its capacity is up to 3200Amp.Its disconnection capacity for low
capabilities values not less than 15KA and each pole provided with
thermal element able to compress(70 -100%) of breaker capacity to
protect against increasing current and three is magnetic element
which is fixed or compressed with taken in account the international
standard.
8-4 Types of protection used in our project

1) Over-current Protection.
2) Earth Fault Protection.
3) Short circuit current protection.
8-4-1 Over-current protection

Over-current protection is that protection in which the relay picks
up when the magnitude of current exceeds the pickup level. The
basic element in Over-current protection is an Over-current relay
which is connected to the system, normally by means of current
transformers.
Over-current protection includes the protection from overloads.

This is most widely used protection. Overloading of a machine or
equipment generally means the machine is taking more current than
its rated current. Hence with overloading, there is an associated
temperature rise. The permissible temperature rise has a limit based
on insulation class and material problems. Over-current protection
of overloads is generally provided by thermal relays.
Over-current protection includes short-circuit protection. Short

circuits may be phase faults, earth faults or winding faults. Short-
circuit currents are generally several times (5 to 20) full load
current. Hence fast fault clearance is always desirable on short-
circuits. 148

When a machine is protected by differential protection, the over-

current is provided in addition as a back-up and in some cases to
protect the machine from sustained through fault.
Several protective devices are used for over-current protection these
include:
1- Fuses.
2- Circuit-breakers fitted with overloaded coils or tripped by over-
current relays.
3- Over-current relays in conjunction with current transformers.
4- Applications of Over-current Protection.
Over-current protection has a wide range of applications. It can be
applied where there is an abrupt difference between fault current
within the protected section and that outside the protected section
and these magnitudes are almost constant.
The over-current protection is provided for the following:

1) Transformer Protection
Transformers are provided with over-current protection against

faults, only, when the cost of differential relaying cannot be
justified. However, over-current relays are provided in addition to
differential relays to take care of through faults. Temperature
indicators and alarms are always provided for large transformers.
Small transformers below 500 kVA installed in distribution system
are generally protected by drop-out fuses, as the cost of relays plus
circuit-breakers is not generally justified Line Protection.
2) feeders protection
The lines (feeders) can be protected by

(a) Instantaneous over-current relays.
(b) Inverse time over-current relays.
(c) Directional over-current relay. 149
Lines can be protected by impedance or carrier current protection

also.

3) Motor Protection
Over-current protection is the basic type of protection used against

overloads and short-circuits in stator windings of motors. Inverse
time and instantaneous phase and ground over-current relays can be
employed for motors above 1200 H.P. For small/medium size
motors where cost of CT's and protective relays is not economically
justified, thermal relays and HRC fuses are employed, thermal
relays used for overload protection and HRC fuses for short-circuit
protection.
4) Protection of Utility Equipment

The furnaces, industrial installations commercial, industrial and
domestic equipment are all provided with over-current protection.
8-4-2 Earth-fault protection

Earth-fault protection called Ground fault protection in U.S.A.
This type of protection senses earth fault current. When the current
flows through earth return path ,the fault is called earth fault .Other
faults which do not involve earth are called phase faults. Since earth
faults are relatively frequent ,earth fault protection is necessary in
most cases. When separate earth fault protection is not economical
,the phase relays sense the earth faults currents. However such
protection lacks sensitivity .Hence separate earth fault protection is
generally provided. Earth fault protection responds to single line to
ground faults and double line to ground faults .The current coil of
earth fault relay is connected either in neutral to ground circuit
.Core balanced CTs are used for earth fault protection.
8-4-3 Short circuit protection

Short circuit currents will only occur under fault conditions and 150
they may be very high indeed .Such currents will open the
protective devices very quickly . The clearance time of protective
devices is governed by adiabatic equation.
8-5 Calculation of short circuit current

We must calculate the short circuit current which path throw the
electrical circuit ,as a result of 3-Φ short circuit at the rear of the
outgoing from the distribution board as a purpose to choosing the
breaking capacity and protect the electrical contactors
To calculate the 3-Φ short circuit current ( Is.c ) from the equation :
I sc =Us/Zf=1.05 Un/Zf
Where :
Us: phase volt at no load
Un : phase volt at load
Zf: the total impedance between source and the short circuit
position
8-5-1 Steps of impedance calculations used in short

circuit current calculations :
The equivalent impedance at medium voltage :
The impedance can be neglected because of its small value .

however to increase the accuracy this form is used to calculate it at
low voltage side :
1. we neglect the equivalent resistance ( Rseq )
2. calculate the equivalent reactance ( Xseq ) in mΩ
By using equation :
Xseq = 3Us2 /sc KVA
Xseq = 3(1.05*220)2 / sc KVA
Note : 151
In our case of study the (sc KVA) = 50000 KV

( Rseq ) = 0.047 mΩ
( Xseq ) = 0.316mΩ
The equivalent impedance of low voltage transformer :
The equivalent impedance can be calculated by using the equation :
Zs.c = 3Us2 *Us.c /KVA
Zs.c = 3 (1.05 * 220 ) 2 *Us.c /KVA
Where:
(KVA)is the rating of the transformer and Us.c is between 0.04 to

0.07
Impedance of the circuit breaker :
The impedance (Z s.c) = 0.15 mΩ is assumed .
Impedance of cables and conductors :
Assuming that the equivalent reactance ( Xeq ) = 0.15 mΩ per

meter length of cable.
And calculate the equivalent resistance per meter from the equation
:
( Req ) =
Where ( ) is the resistivity of the conductors materials as follow :
= 22.5 Ω.mm2 per meter for the copper and = 33 Ω.mm2 per
meter for the Aluminum
and (A) is the cross section area in mm2
Impedance of the bus duct :
Assuming that the equivalent reactance ( Xeq ) = 0.15 mΩ and the
resistance of it is calculated as in the case of cables . 152
Note: In our design, a bus duct from transformer to the main- board
is used.

8-5-2 calculation of short circuit current for block (1)

* Calculate Impedance of transformer at LV Side:
As the rating of transformer=1000 MVA

So Impedance of the transformer ( Z s.c ) is calculated from the
equation
Zsc= 3Us2 *Us.c / KVA
Zsc = = 8Ω
Reactance of C.B = 0.15
Total impedance Zt = 8+0.319+0.15 = 8.469mΩ
So short circuit current at L.V .S of transformer is
Isc = = 27.27 KA
So rating of short circuit breaking in L.V.S of transformer assume

to be (30KA )
So the breaking capacity of the C.B. = V Isc
*Calculate impedance of main board(built(5)]:
Assume we use copper bus duct from transformer to main board

with Cross section area =70 and length=33m so
Req = = 10mΩ
Xeq = 0.08×33 = 2.6mΩ

Zeq =10.33mΩ 153
Zt = 10.33+0.3+8+0.319 =18.95mΩ

Isc = = 12.19 KA
Isc For C.B = 15KA

So the breaking capacity of the C.B =10.4MVA
*Calculate impedance of main board[built(13A) normal ]
Cross section area = 50 and length = 1m
Req = = 0.45mΩ
Xeq = 0.08×1= 0.08mΩ

Zeq= 0.451mΩ
Zt = 0.451+0.3+8.319 = 9.07mΩ
ISC = = 25.46 KA
ISC For C.B = 30 KA

So the breaking capacity of the C.B= 1.732×0.4×30 = 20.7 MVA
*Calculate impedance of main board(built[13A]) critical

with Cross section area = 70 mm2 and length=1m
Req = = 0.321 mΩ
Xeq = 0.08×1= 0.08mΩ
Zeq= 0.33mΩ
Zt=0.331+0.3+8+0.319=8.95mΩ
ISC = = 25.78KA
ISC For C.B = 30KA

So the breaking capacity of the C.B =20.7MVA 154
*Calculate impedance of main board(built[13B]) normal


with
Cross section area =300 mm2 and length = 45m
Req = = 3.36mΩ
Xeq = 0.08×45 = 0.08mΩ
Zeq =4.6mΩ
Zt = 4.6+.3+8+0.319 = 13.22mΩ
Isc = = 17.47KA
Isc for C.B = 20KA
*Calculation impedance of main board(built[13B]) critical

with Cross section area=120 and length=42m so
Req =22.5*42 / 120 = 7.8mΩ

Xeq = 0.08×42=3.36mΩ
Zeq = 8.49 mΩ
Zt = 8.49+0.3+0.319 = 17.1mΩ
Isc = = 13.5KA
Isc For C.B = 15KA

8-5-3 Calculation of short circuit current for other blocks:

block (2)
155

8-5-4 Calculation of short circuit current for other blocks:

block (2)
Table 8.1 shows calculation of short circuit for

Load Req X eq Z Z
eq I t I block (2)
breaking
sc sc MVA
mΩ mΩ mΩ mΩ KA capacity(KA) breaking
capacity
Mall 7.6 6.5 10 17.17 13.4 15 10.4
36.9 6.5 37.4 44.5 5.2 7 4.9
Office 7 4.6 8.3 15.5 14.8 15 10.4
8.7 4.64 9.8 17 13.5 15 10.4
Hotel 10.9 7.2 13.1 20.2 11.4 15 10.4
21.4 7.2 22.6 29.7 7.76 10 6.9
block(3) as same as block (6)
Table 8.2 calculation of short circuit for block (3,6)

Load Req Xeq Zeq Zt Isc Isc MVA
mΩ mΩ mΩ mΩ KA Breaking breaking
capacity KA capacity
Building
10.5 2.6 10.8 19.4 11.9 15 10.4
(5)
Building 7.97 5.25 9.5 18.1 12.7 15 10.4
(10) 12.3 5.24 13.3 21.9 10.5 15 10.4
Building 16.9
3.8 3.2 5.01 13.02 20 13.86
(13) 5
9.7 3.2 10.2 17.4 13.2 15 10.4
Building 0.75 0.4 0.85 8.02 28.8 30 20.8
(13) 1.6 0.4 1.61 8.8 26.1 30 20.8
156

block(4)
Table 8.3 calculation of short circuit for block (4)

mΩ mΩ mΩ mΩ KA breaking cap breaking
capacity
Building 18.6 4.6 19.1 26.3 8.7 10 6.9
(5) 21.2 5.2 21.8 29 7.9 10 6.9
Building 0.75 0.4 0.85 0.8 28.8 30 20.8
(13A) 1.6 0.4 1.61 8.8 26.6 30 20.8
Building 6.1 5.2 8 15.2 15.1 20 13.8
(13A) 15.6 5.2 16.4 23.6 9.7 10 6.9
Building 30 2.6 4 11.1 20.6 25 17.3
(13B) 6.1 2.6 6 13.8 16.7 20 13.8
Building 6.9 5.9 9 16.2 14.2 15 10.4
(13B) 37 5.9 37.4 44 5.1 7 4.85
block(5)
Table 8.4 calculation of short circuit for block (5)
mΩ mΩ mΩ mΩ KA breaking breaking
capacity
Build 0.6 0.4 0.7 9.3 24.8 30 20.8
ing 1.6 0.4 1.62 10.2 22.6 25 17.3
block(7)
calculation of short circuit for block (7) as same as block (1) 157

references
References
‫ الكىد المصري ألسس تصميم وشروط تنفيذ التىصيالت الكهربية في المباني‬
 El-Sewedy cables catalogs.
 sunil S.Rao,"Switchgear and protection".
 B.M. Weddy, B.J. cory, "Electrical power system",4th edition 1998.
 IEC 60364-1: Electrical installations of buildings — Part 1:

Fundamental principles, assessment of general characteristics,
definitions. International Electrotechnical Commission, Geneva.
 Geoff Cronshaw: Earthing: Your questions answered. IEE Wiring

Matters, Autumn 2005.
 Merlin Gerin Guide, Section 2.3: Characteristics of TT, TN and IT

systems.
 John Whitfield: The Electricians Guide to the 16th Edition IEE

Regulations, Section 5.2: Earthing systems , 5th edition
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158
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references
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 http://www.superiorgrounding.com/soils.html
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 Electric power quality, Dr. A.A Salam
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storageplant-
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Web site
 http://www.greenrhinoenergy.com/solar/
 http://www.i15.p.lodz.pl/strony/EIC/res/Description_of_technology_pv.html
 http://www.buildingwithawareness.com/blog/2009/03/determining-the-actual-
power-output-of-photovoltaic-pv-panels-for-green-homes/
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FA C U L T Y O F E N G I N E E R I N G

Ahmed Gomaa abd El-rahman

Electrical minds team

2.3 Type of Substation bus scheme-----------------------------------18