Abstract

North Delhi Power Limited, NDPL is a 51:49 JV of M/s TATA Power Company Limited and Govt. of Delhi (GoNCTD), and carries the distinction of being the first success story of Power Sector Reforms in India. NDPL was instituted on July1, 2002 and serves a population of about 4.5 million people spread across 510 sq kms. It has a registered consumer base of about 1 million, a peak load of 1100 MW and an annual energy consumption of around 6400 MUs. NDPLs Revenue has shown a CAGR of 18% (from Rs 1095 Crores in 2002-03 to Rs 2474 Crores in 2007-08). The gain in efficiency can be gauged by the fact that Tariff increase has contributed to only 4% to the total Revenue growth, the rest being solely on the basis of improvements in revenue cycle processes. NDPL has successfully reduced AT&C Losses by over 66% since takeover in July 2002 (from an opening loss level of 53% down to below 19% at present). The various measures taken to achieve this Loss Reduction include: Energy Audit up to the DT level. Implementation of HVDS & LT ABC schemes in Theft prone areas. Replacement of old erroneous electromechanical meters with accurate Electronic meters. Automated Meter Reading for all SIP & KCG consumers (contributing to almost 60% of the Revenue) Aggressive Enforcement activities with scientific inputs & analysis. HVDS implementation Public participation in controlling Theft through the concept of Social Audit. Collaboration with NGOs for creating awareness in Slums/JJ clusters regarding the dangers associated with Direct Tapping of electricity from live wires.

Power Supply situation in NDPL has improved over the years owing to the latest technological implementations and integrated approach to maintenance management institutionalized by NDPL. The International Reliability Indices are as shown in the Table below:

On Takeover SAIDI(hrs) 110 SAIFI(nos.) 55 CAIDI(hrs.) 2

02-03 70 35 2

03-04 36 18 2

04-05 23.6 12.6 1.87

05-06 9.3 5.3 1.75

06-07 6.9 5.2 1.3

07-08 6.2 6.6 0.9

08-09 8.2 6.6 1.2

System Average Interruption Duration Index (SAIDI): Average time for which the consumers face interruption System Average Interruption Frequency Index (SAIFI): Average frequency of sustained interruptions per customer over a predefined area. Consumer Average Interruption Duration Index (CAIDI): Average time required to restore service to the average customer/sustained interruption.

The demand for electricity continues to exceed the supply in almost all the developing countries. The availability of a reliable and economic form of electrical energy is a pre-requisite for economic growth and social development The electrical energy losses in India as per estimates are of the order of 21-23% as compared to 8-10% in developed countries. Many methods have been proposed to reduce the losses in distribution system.

Table of Contents
2

S. No. 1 2

Contents Chapter-1, Introduction Chapter-2, Data requirement Chapter-3, Design criteria a. Equipments used b. Planning Philosophy c. Analysis Criteria d. Planning Criteria. Chapter-4, Analysis of existing system a. DETECTION OF CABLE FAULTS b. AERIAL BUNCH CONDUCTOR c. Transformer oil leakage Chapter-5, Zones at a glance
a. b. c. d. Basic Introduction Equipment Modeling Network Modeling Load Modeling

Page Number 5 6-7

8-17

18-22

23-28

6 7

Conclusion BREAKDOWN
Recovery procedure

29 30

CHAPTER-1
3

INTRODUCTION
1.

Objectives:

This study is to evaluate the performance of 11kV feeders of Zone-411 and Zone-418 starting from the secondary side of the power transformers and including the distribution transformer considering the present network state and a load growth over next 2 years. The objectives set are as below

Study existing 11kV System adequacies Plan and design the 11kV system to meet the load growth over horizon of 2 years to ensure Voltage conditions to be within permissible limits Optimum energy losses Optimum conductor/ cable loadings Meet (N-1) contingency Maximum reliability

Project investment plan

2.

Methodology:

A systematic approach shall be taken to analyze the Network and to prepare a Investment Plan The methodology shall be as follow11kV Network Documentation and validation 11kV Network Mapping/ Modeling in CYME software Analysis of the existing system Prepare Final Report

CHAPTER-2
4

DATA REQUIREMENT
This chapter elaborates the details on the data requirement for analysis and planning procedure for 11kV Network for each zone & KCG Consumer.

1. Consumer Data:
Category wise number of consumers and connected load that including the HT consumers

2. Geographic Map :
Geographic map of the zone showing all sub-transmission and distribution networks shall be taken from NDPLs GIS

3. Power Source:
Power in the Zone - Grid Substations and 11kv Feeder

4. Operational Parameters:
Equipment data such as Cables, Conductors, Transformers etc. Sub-transmission Breakdowns Distribution Transformer Failures Tripping on 11kV Feeders/ Lines Consumer Outages

5. Electrical Network details:

Electrical network details SLDs with conductor/cable sizes, lengths, transformer locations, transformation capacities, Capacitors, HT consumers and consumers load Parameters of all equipment ,devices and conductors Load data, peak load data, diversity factors, power factors etc.
5

6. Load Data:
The planning study shall be based on actual feeder load conditions and measurement taken at various points in the system. Various operational and load data required Peak Load on each transformer/ feeder and corresponding actual voltages Diversity Factors at various levels Power Factor at various voltage levels

7. Data Validation:
The network data shall be obtained from GIS and validated with the actual Zonal data.

CHAPTER-3
DESIGN CRITERIA
6

The prime objective of the planning the 11kV Network is to ensure the quality and reliable supply as per regulatory requirements to the consumers with optimum technical losses and also meet the growing power demand with minimum 2 years of time horizon.

A. Equipments Used: Power transformer Capacitor bank CT & PT Lighting arrester Busbar coupler Circuit breaker Isolators Earth switch

A1) Power Transformer

A transformer is a device that transfers electrical energy from one circuit to another through inductively conductorsthe transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF), or "voltage", in the secondary winding. This effect is called mutual induction.

Components in power transformer

1.

Main tank: - it consist of oil, main windings, and all the working part of the transformer.
Its size is depending upon the kva rating of the transformer.

2.

Core:- Core of the transformer is either in square or rectangular in size. It is further divided
into two parts. The vertical position of the core is limbs and horizontal position of the core is yoke of the core. Core is made up of laminations to reduce the eddy current losses get minimized. This lamination is insulated by using insulations line varnish or thick paper. Paper insulation is used for low voltage transformer and varnish is used for high voltage transformer. There are two types of core :Shell and iron core.

3.

Windings

- Conducting material is used in the windings of the transformer. Usually the

windings are in concentrically to minimize the flux leakages. There are two types of windings. The coils are wound on the limbs and are insulated from each other in the basic transformer the two windings wound on the two different limbs. Due to this leakage flux increases which affects the transformer efficiency or performance so it should be necessary that the windings should be very close to each other to increase the mutual inductance and stray capacitance to improve the high frequency response. Such cylindrical coils are used in core type transformers and sandwich coils are very commonly used in shell type transformer here each high voltage winding lies between two low voltage windings such subdivisions of windings into small portions reduce the flux leakages.

4.

Insulation:- there are no of types of insulations that are used in the transformer
them are :a) Paper insulation. b) Cotton insulation c) Fibre based board insulation.

some of

5.

Radiators: - control the temp of the oil. Cooling of the oil is done by the 4 methods :a) ONAN b) ONAF c) OFAF d) OFWF

6.

Conservator controls the expansion of oil by temp. Conservator tank consists of oil level
which depends on the operation of the transformer. The oil expands in summer with the increase in load and the oil contracts with decrease of the load. Conservator is a small auxiliary oil tank that may be mounted above the transformer and connected to the main tank by a pipe. Its main function is to keep the main tank of the transformer completely filled with the oil in all circumstances. When the oil in the tank contracts then the conservator gives the oil to maintain the oil level in the tank. When the oil in the tank expands then the conservator takes the oil.

7.

Off load tap changer

A transformer

tap is

connection

point

along

a transformer winding that allows a certain number of turns to be selected. This means, a transformer with a variable turns ratio is produced, enabling voltage regulation of the output. The tap selection is made via a tap changer mechanism . 8.

Breather:

- We supply Silica Gel Breather which is largely in demand in the Transformer

Industry because they provide an economical and efficient way of keeping a tab over the level the moisture, entering in the Transformer. Silica Gel Breather is made from the finest quality raw material of Blue Silica Gel to sustain the test of time. They are available in two varieties viz. Clear View Type and Aluminum Type. The Silica Gel Breather, we provide, is up to the capacity of 2000kva. Our quality speaks for itself it has brought our name among some of the finest Silica Gel Breather Supplier and Exporters. Clear View Type Size. (Kg.) 0.120 0.250 0.500 0.750 1 1.5 2 3 5 6 8 10 15 Aluminum Body Size. (Kg.) 0.250 0.500 0.750 1 1.5 3 4 5 -

9.

OTI
indicator

:-

oil

temperature

A2) CT & PT
9

current transformer :A current transformer (CT) is a type of instrument transformer designed to provide a current in its secondary winding proportional to the alternating current flowing in its primary. They are commonly used in metering and protective relaying in the electrical power industry where they facilitate the safe measurement of large currents, often in the presence of high voltages. The current transformer safely isolates measurement and control circuitry from the high voltages typically present on the circuit being measured. Current transformers are used extensively for measuring current and monitoring the operation of the power grid. The CT is typically described by its current ratio from primary to secondary. Often, multiple CTs are installed as a "stack" for various uses (for example, protection devices and revenue metering may use separate CTs). Similarly potential transformers are used for measuring voltage and monitoring the operation of the power grid. Shapes and sizes can vary depending on the end user or switchgear manufacture. Typical examples of low voltage single ratio metering current transformers are either ring type or plastic moulded case. Depending on the application and voltage range of Cts, they could be sub-divided as below: Tank Type Current Transformers Cast Resin Current Transformers Bushing Type Current Transformers Window Type Current Transformers

Potential Transformer
Potential Transformer is designed for monitoring single-phase and three-phase power line voltages in power metering applications. The primary terminals can be connected either in line-to-line or in line-to-neutral configuration. A Potential Transformer is a special type of transformer that allows meters to take readings from electrical service connections with higher voltage (potential) than the meter is normally capable of handling without at potential transformer. The Potential Transformers, according the applications, could be sub-divided as below: Capacitive Potential Transformer Cast Resin Inductive Potential Transformer

A3) Lightning arrester

10

A lightning arrester is a device used on electrical power systems to protect the insulation on the system from the damaging effect of lightning. Metal oxide varistors (MOVs) have been used for power system protection since the mid 1970s. The typical lightning arrester also known as surge arrester has a high voltage terminal and a ground terminal. When a lightning surge or switching surge travels down the power system to the arrester, the current from the surge is diverted around the protected insulation in most cases to earth.

A4) Bus bar coupler :Depending on the switchgear, and the loads that the switchgear is feeding, they could be coupled for a couple of different reasons (here are three common reasons): 1- if the buses are being fed from two different transformers, if one of the transformers fails, the buses can be coupled so one transformer can feed loads coming off the other side of the buses, that the failled transformer originally fed. 2- if one transformer is providing more KVA than the other, the buses can be coupled to transfer load to the other switchgear, providing a more balanced situation, as far as transformer loading is concerned. 3- For future considerations, buses may be tied parallel to each other to provide KVA for future loads. This prevents the need for costly units that are not tied to existing buses, as well as installations of new transformers, or ties to existing lines.

A5) 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, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse, which operates once and then has to 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. A6 In electrical engineering, a disconnector or isolator switch is used to make sure that an electrical circuit can be completely de-energised for service or maintenance. Such switches are often found in electrical distribution and industrial applications where machinery must have its source of driving power removed for adjustment or repair. High-voltage isolation switches are used in electrical substations to allow isolation of apparatus such as circuit breakers and transformers, and transmission lines, for maintenance. Isolating switches are commonly fitted to domestic extractor fans when used in bathrooms in the UK. Often the

11

isolation switch is not intended for normal control of the circuit and is only used for isolation. Isolator switches have provisions for a padlock so that inadvertent operation is not possible (see: Lockout-Tagout). In high voltage or complex systems, these padlocks may be part of a trapped-key interlock system to ensure proper sequence of operation. In some designs the isolator switch has the additional ability to earth the isolated circuit thereby providing additional safety. Such an arrangement would apply to circuits which inter-connect power distribution systems where both end of the circuit need to be isolated. The major difference between an isolator and a circuit breaker is that an isolator is an offload device intended to be opened only after current has been interrupted by some other control device. Safety regulations of the utility must prevent any attempt to open the disconnect or while it supplies a circuit.

B.

Planning Philosophy:

o Minimum number of consumers affected by an outage in an area. o Meet N-1 contingency for 11kv Network o Automate the vital points after study so as to achieve the high reliability in the network. o Minimum technical loss level

C.
1. 2.

Analysis Criteria:

Time Horizon: The time horizon considered for the study is 2 years Administrative unit for analysis: The analysis shall be carried out 11kV Network for
all Zones. The Zones shall be selected on the Categories defined by NDPL viz. Stars, Destroyers, Bleeders and Devastators.

3.

Voltage Regulation

:The allowable voltage variations in 11kV Feeders under peak

loading conditions and normal system operations shall be between +6 & -9% , 5% for MW Consumer of nominal Voltage considered as 11 KV

12

4.

Feeder Head Voltage: The feeder head voltage shall be assumed to be the mean of the
maximum and minimum voltage occurred during the last year .

5. 6.

Technical Loss level: The optimum peak technical loss level shall be maximum 4 %. Power Transformers : Each 66 or 33/11 kV Grid substation shall have at least 2 nos of
Power Transformers of adequate transformation capacity to meet N-1 contingency

7.

Distribution Transformers: The Distribution Transformers to be recommended shall

be of standard ratings as per NDPL practice i.e. 25kVA, 63 kVA, 100kVA, 160kVA, 250kVA, 315kVA, 400kVA and 630kVA. However existing 1000kVA transformers shall continue to operate as long as they are not over loaded.

8.

Distribution Transformer Loading:

The Distribution Transformers shall be

operated at 50-65% (Optimum is 60%) of their rated capacity and shall be recommended for augmentation when the maximum demand on the transformer is nearing 80% of the rated capacity. 9.

Power Factor: HVDS:

The power factor limit shall be maintained at 0.85 (Lag) at 11kV

Distribution Transformers. 10. The loading for HVDS (Only Single Phase) shall be taken as a concentrated

Lumped Load for the corresponding feeder. 11. Analysis

Loading Condition:

The analysis shall be carried out for 11kV Network

considering the last year NDPLs peak load conditions. However individual Distribution transformer maximum day peak loads for corresponding month shall be taken for study.

D.

Planning Criteria:

1. Choice of Cables:
The choice of cables for 11kV Network shall be as per NDPL standard practice viz.-

13

Cable ID *

Resistance (Ohms/ Km)

Reactance (Ohms/ Km)

Susceptance (S / Km)

Rated Current under nominal conditions (A) 260 140 175 196 168 224 260

Rated Current under exigency (A) 290 160 200 220 188 252 290

11KV_3C_150_AB C 11KV_3C_150_PIL C 11KV_3C_240_PIL C 11KV_3C_300_PIL C 11KV_3C_150_XLP E 11KV_3C_240_XLP E 11KV_3C_300_XLP E

0.206 0.206 0.125 0.1 0.206 0.125 0.1

0.114 0.089 0.085 0.084 0.114 0.106 0.103

80.108 177.49 158.36 235.613 80.108 95.816 103.66

2. Choice of conductors:
The choice of overhead conductor shall be standardized to DOG conductor Rated Current under nominal conditions (A) 260 154 200 86 Rated Current under exigency (A) 290 183 238 102

Conductor Type DOG RABBIT RACCOON SQUIRREL

Diameter (cm) 1.415 1.050 1.227 0.633

GMR (cm)

Resistance (at 45 C) 0.324 0.643 0.431 1.621

0.551 0.409 0.478 0.247

3. . HT Consumers:
The actual peak load as per Meter data

4. . HVDS:
HVDS load shall be assumed with 40% Load Factor for Residential Loads and 60% Load Factors for Commercial and other loads

5. . Voltage Regulation:
14

+6% to -9% over declared System voltage of 11kV Nominal Voltage: Highest Voltage: Lowest Voltage: 11kV 11.66kV 9.9 kV

6. Circuit Lengths Limits (Without Line Capacitors):

DOG: 3x150 HT ABC: 3x95 HT ABC: XLPE Cable: 11 km 15 km 6 km 15 km

7. 11kV Feeder Loading Limits under peak:

Loading Limit on Feeder: Emergency Limit: Load Limit DistributionNormal Feeding: Load Transfer: Load Growth Provision: 2 MVA 0.5 MVA 2 MVA 4.5 MVA 5.5 MVA

8. Optimum number of Sections on Feeder and Load:

Normal Feed: 2 Sections with 1 MVA Load each

9. . No of Feeds per stage: 10. 11.

2 Nos of Feeds per Section

Voltage Unbalance Limits: Load Unbalance Limit:

1%

10%

15

12.

Distribution Transformer (DT) : overloaded DT ( >80%) shall

be augmented by higher rated DT . if existing rating is 630 KVA & above then additional DT shall be installed of appropriate capacity ( <1000 KVA).

CHAPTER-4
ANALYSIS OF EXISTING SYSTEM
After getting the desired input data as mentioned in the previous section, the existing 11kV Network of a zone shall be carried out in detail using the CYME-Dist software to assess the following parameters16

 Voltage variations:
o Voltage at each node/ bus section o % voltage variation w.r.t. Input Voltage o Voltage Limit Violations

Feeder wise Peak Power

technical loss in the Zone

Loss so as to arrive at % loss in 11kV system

Identification of inadequacies in the existing 11kV Network in terms ofo Overloading of Distribution Transformer o Overloading of Lines/cables o Power Factors and Reactive compensation requirement o 11kV Feeder Level (N-1) contingency o Reliability level of the network

DETECTION OF CABLE FAULTS

INTRODUCTION
In transmission system, sometimes due to some abnormal conditions such as aging of cables, high loading on cables etc. our cables get faulty. Now, in case of high voltage underground cables normally used for the power transmission from Transco to sub17

station, we need to pre- locate the fault location before starting our proceedings towards repairing it to decrease the unnecessary labour work, decrease repairing cost & overall to increase the efficiency of repairing the fault.

COMPACT SYSTEM FOR CABLE FUALTS

Now days NDPL is using advance GERMAN TECHNOLOGY named as SEBA KMT control unit to detect the underground cable faults. It is a compact system for detecting cable faults in underground cables of rating 11kv, 33kv, 66kv & sometimes its also used for detecting faults in overhead ABCs (Arial Bunch Conductor) used now days for distribution system. The system is consists of an oil filled capacitor bank used to obtain high voltage DC supply, which is further used to pass surge voltage during Pre & Pinlocation tests. System is also consists of a timing switch which can be controlled manually, this switch is used to provide the clock cycle (timing cycle) for charging & discharging of the capacitor bank during pin- location test.

PROCEDURE FOR FINDING FAULT LOCATION IN A

CABLE
Firstly for finding the fault location we connect the faulty cable to the system at no load. And we also need a normal AC power supply to the unit, which is normally above 230V, this supply is used by the capacitor bank, which gives out the high voltage DC supply, which is used as a surge voltage during Pin & Pre- location tests. Now, the steps involved in testing cables are: Testing Pre - location Pin - location

TESTING
This step involves the testing of cable for finding the faulty phase of the cable. In this one by one each phase is applied with the full load voltage, now the phase which doesnt able to hold this full load voltage, that phase is the faulty one.
18

 Pre -location
This test is performed to find out the average distance, nearby which the fault may exist in the cable. During this we get two curves which shows the distance where fault may exist. RED CURVE Reference curve BLUE CURVE Gives the fault location

Pin location
Pin location test is used to find out the exact position of the fault in the cable. In this test the faulty cable is attached to the capacitor bank unit & then a DC surge voltage is applied to the cable according to the timing cycle. An acoustic detector & a surge detector is used to detect the exact fault location. With these detectors, we trace the route of the cable around the suggested distance after pre- location test & detect the acoustic & surge signal near the fault, which appears due to the discharging of the capacitor bank at the fault. The degree of acoustic & surge signal predict the exact location of fault in the cable. Sometimes in Pre- location we may not get the proper graph of the cable, which create problems in detecting the fault location, then some other practical techniques are followed to find the fault location such as murray loop test.

AERIAL BUNCH CONDUCTOR

INTRODUCTION:
This conductor is commonly used in HT/LT networks to replace the DOG/SQURIAL/RECCON conductor. For HT, 11kv underground cables XLPE/PILCA is changed with overhead HT ABCs of size 3*150+1*155mm.

19

In HT ABCs there are four wires, 3 main phase wires of 150mm each, one neutral wire of 155mm. These cables are used in HVDS systems & in near the 11KV substations where the high voltage distribution is overhead. In LT networks overhead DOG/SQURIAL/RECCON conductors are replaced with LT ABCs of size 3*150+1*150+1*16mm. In LT ABCs there are five wires, 3 main phase wires of 150mm each, one neutral wire of 150mm and one is used for street light purpose which is of 16mm.These cables are used in domestic distribution purposes.

ADVANTAGES OF USING ABC CABLES:

These cables have a higher current carrying capacity. Distribution power losses are reduced using these cables. Flexibility of increasing number of conductors on a pole. These cables required less maintenance. ABCs makes the distribution system safer. Its easy to work with the ABCs during their maintenance and repairing of faults. ABCs distribution system looks better than the older ones.

Transformer oil leakage

1. Causes of transformer oil leakage.
20

Due to overheating of transformer . Due to over loading of transformer. Due to line fault of transformer. Due to failure of gas kit.

2. Safety point of oil leakage of transformer.

Using buchholz relay in transformer. Using magnetic oil level gauge. Using oti and wti .

3. How to stop oil leakage in transformer.

Using silicon putty up to temperature 120 degree celsius. Using titanium putty up to temperature 170 degree celsius.

4. Description of putty use to stop oil leakage.

1. Silicon putty. Composition: hardner & resin in 1:1 ratio, its settling time is 5 min. 2. Titanium putty. Composition:hardner & resin in 1:3 ratio, its settling time is 20 min.

21

CHAPTER-5
ZONE AT A GLANCE
A. Basic Introduction In pitampura III substation grid there are: 2 main circuit supply of 66kv from pitumpura II Three power transformers 33 feeders

B. Equipment Modeling:
Technical attributes of various electrical network equipments like transformers, sources, cables; overhead lines, capacitors and protective devices are considered for the study. Data for these equipments has been collected from the manufacturer catalogues and the same equipment parameters were given below. a.

Cable Parameters:
Cable ID * Resistance (Ohms/ Km) Reactanc e (Ohms/ Km) Susceptanc e (S / Km) Rated Current under nominal conditions (A) 260 200 140 175 196 Rated Current under exigency (A) 290 220 160 200 220
22

11KV_3C_150_A BC 11KV_3C_95_AB C 11KV_3C_150_PI LC 11KV_3C_240_PI LC 11KV_3C_300_PI LC

0.206 0.32 0.206 0.125 0.1

0.114 0.123 0.089 0.085 0.084

80.108 67.54 177.49 158.36 235.613

11KV_3C_150_X LPE 0.206 0.114 80.108 168 188 11KV_3C_240_X LPE 0.125 0.106 95.816 224 252 11KV_3C_300_X LPE 0.1 0.103 103.66 260 290 * A cable of 11KV_3C_300_XLPE represents 11 KV cable consists of 3 cores each having 300 mm cross-sections and with XLPE insulation. b. Overhead Conductor Type DOG RABBIT RACCOON SQUIRREL

conductor Parameters:
Diameter (cm) 1.415 1.050 1.227 0.633 GMR (cm) Resistance (at 45 C) 0.324 0.643 0.431 1.621 Rated Current under nominal conditions (A) 260 154 200 86 Rated Current under exigency (A) 290 183 238 102

0.551 0.409 0.478 0.247

c. Shunt

Capacitor Parameters

Rated KVAR Rated kV Capacitor ID * (Per phase) (L-N) 0.433KV_220KVAR_CAP 73.33 0.24 0.433KV_300KVAR_CAP 100 0.24 * A capacitor of 0.433KV_220KVAR_CAP represents capacitor supplying 220 KVAR at 0.433 KV. d. Transformer

Parameters
PRIM VOLT (KV) SEC VOLT (KV) IMPEDANCE (Ohms)

NO LOAD Transformer ID * X/R LOSS (KW) 11/0.433_5%_250KVA 11 0.43 4.5 3.72 0.37 11/0.433_5%_315KVA 11 0.43 5 3.72 0.45 11/0.433_5%_400KVA 11 0.43 5 3.72 0.53 11/0.433_5%_500KVA 11 0.43 5 4.38 0.7 11/0.433_5%_630KVA 11 0.43 5 4.38 0.7 11/0.433_5%_990KVA 11 0.43 5 4.38 1.4 11/0.433_5%_1000KVA 11 0.43 5 4.38 1.4 * A transformer of 11/0.433KV_5%_250KVA represents the 11KV/ 0.433KV step-down transformer of capacity 250 KVA and impedance of 5 %.

23

C. Network Modeling:
After preparation of the equipment database, the Grid substations are modeled by defining the internal arrangement of substations. Distribution network model is created as per the connectivity details shown in the Single Line Diagrams. In this model all details like section and equipment names (Location based), bus bar arrangement of distribution substation all the corresponding technical data of respective equipments that is required for analysis has been fed as input.

D. Load Modeling- Input Data:

Distribution Transformers Peak loads (metered) during summer 2008 have been considered. Wherever the metered data for the Distribution Transformers is not available, Feeder peak current is considered to derive the loads.

24

1. Load Growth :
1. Sum of peak load (2008) of all 11 KV Feeders = 35000 KW 2. MDI of KCG Consumers in year 2008 - 17400 KW 3. Approximate Peak Load contributed by HRB and HCB Connections = 35000-17400 = 17600 KW 4. Approximate Load added for HCB/HRB connections per year = 1500 KW 5. Load Growth = 1500*100/17600 = 7.28 %

25

Conclusion
Based on the study of 11kv/440v supply network, a detail list of works to be executed prepared under Capex-11-12. The works to be carried out during 11-12 are kept under following categories.

1)Distribution transformers:i) Augmentation of capacity of DTs which are loaded < 70% ii) Placement of new DT where augmentation is not possible

2)System Improvement Works:i) Re-conductoring of under-rated 11 kV sections ii) New 11 kV inter-connectors iii) New 11 kV feeders iv) Replacement of old 11 kV switches

BREAKDOWN
26

Recovery procedure
In a normal distribution system problem of breakdown occurs due to many reasons such as bad weather, ageing of cables, heavy loading etc. NDPL has their own separate staff for the fast recovery of these breakdown problems. Now days with the advancement in technology, automatic detection of breakdown on different sites is very easy with the help of automation engineering by making use of PLC n SCADA , microprocessors etc. During breakdown on any site, first of all DMS gets updated automatically, which when inform the zonal Deputy ZSO about the breakdown & then the breakdown staff of that area is informed about the site and breakdown. Now the breakdown staff tries to recover the fault as soon as its possible.

DMS

Zonal

DEPUTY ZSO

Breakdown unit

27