INDEX

S.NO TOPIC PAGE NO

1 INTRODUCTION 2
2 PCHES 4
SWITCHYARD
3 EHV BUSBAR 6
ARRANGEMENTS
4 EQUIPMENTS IN 12
THE SWITCHYARD
5 TURBINE IN 48
POWER HOUSE
6 EARTHING 51
7 CONCLUSION 54

1. INTRODUCTION:

1
 Food, clothing and shelter were the basic needs of mankind till lately but now we
can say that electricity has become a part of basic needs. Life without electricity has
become unimaginable. There are three ways for the generation of electricity-thermal,
hydel and nuclear. In India, majority of the power is produced utilizing thermal energy.

BRIEF HISTORY OF THE PULICHINTALA HYDRO

ELECTRICAL SCHEME

PULICHINTALA HYDRO ELECTRICAL SCHEME is one of the major power

generating station of the Telengana. The main raw material is water (Hydro) is supplied by
krishna river , pulichintala and Water sources is from pulichintala project, which is about 20
Kms from the jaggaiahpet.
It is officially known as K.L RAO SAGAR. Its main aim to provide irrigation &
water supply. It supplies irrigation facility for 13L acres. It is having of totally 24 gates with
capacity of tmcft at 175 feet (53m) full reservoir level. Its construction began 14 Nov 2010.
The opening ceremony on 7 Dec 2013. It operates under TSGENCO.

Pulichintala Hydro Electrical Scheme installed four powerhouses namely

unit - 1,2,3,4.

Unit -1 : 30MW
Unit -2 : 30MW
Unit -3 : 30MW
Unit -4 : 30MW

A PROFILE OF PULICHINTALA HYDRO ELECTRICAL

SCHEME

2
 Foundation for India’s power sector was laid in the year 1897 with commencement of
2000 kw micro hydel project at Darjeeling, being the load center.

The Andhra Pradesh state electricity board. Here it is often called as APSEB. The
APSEB is responsible for promoting the coordination of generation, transmission and
distribution of electrical energy throughout the state of Andhra Pradesh.

In a step to power sector reforms, APSEB has been divided in to two corporations. i.e.
Andhra Pradesh Power Generation Corporation Limited (APGENCO) and Andhra Pradesh
Power Transmission Corporation Limited respectively on 1st February, 1999.
In a step of state bifurcation AP GENCO has been divided in to APGENCO &
TSGENCO respectively on 2nd June 2014
The project construction in 14 November 2010 and opened on 7 December 2013 and
its cost of 1850 crore rupees. The dam is completely in the Andra Pradesh.

It was constructed across the Krishna river downstream to existing Nagarjuna sagar dam.
Height of dam is around 30 m, length 1050 m and crest elevation is at 10 m.

K.L.RAO SAGAR PULICHINTAL PROJECT DAM

2.PCHES SWITCH YARD:

2.1 INTRODUCTION:

3
 An electrical substation is an assemblage of electrical components including bus
bars, isolators, circuit breakers, transformers, lightning arresters, instrument
transformers etc. electric power between incoming and out going circuits, in substation
takes place through bus bars. We can say, the bus bars are junction points capable of
carrying huge power.
Bus bars are conducting bars to which a number of incoming or outgoing
circuits are connected. Electrical components of each circuit are connected in a definite
sequence such that a circuit can be switched on/offoperations. In PCHES O&M we are
using Double Bus Bar system with quadradone ACSR conductor.

2.2 TASKS OF THE SWITHCH YARD:

a. Protection of transmission system (to isolate faulty network from the healthy
one)
b. Controlling the exchange of power (i.e. to control the power transmission to load
points as per requirements and instructions of LDC.)
c. Maintain the system frequency within targeted limits. (This can be done by
raising/ lowering of generation or load shedding.)
d. Determination of power transfer through transmission lines.
e. Fault analysis and subsequent improvements.
f. Communication: data transfer via power line carrier for the purpose of network
monitoring, control and protection.

2.3SCHEMATIC LINE DIAGRAM OF THE PCHES:

4
Spillway : 755.90M
LeftNOF : 422.60M
RightNOF : 91.50M
Storage : 45.75TMC
No.of Gates : 24Nos

3. EHV BUS BAR ARRNGEMENTS

5
  SINGLE BUS BAR
 SINGLE SECTIONALISED BUS BAR
 DOUBLE BUS BAR
 MAIN & TRANSFER BUS ARRANGEMENT
 DUPLICATE BUS BAR ARRANGEMENT
 THREE BUS SYSTEM: DOUBLE & TRANSFER BUS
 BREAKER AND HALF SYSTEM or 1 ½ BREAKER SYSTEM

3.1 BUS BARS:

The choice of the bus bar scheme for a substation depends upon the degree of
reliability, flexibility and economic justification. The degree of reliability is evaluated by
determining the continuity of service and possible faults.

In electric power distribution, a busbar is a metallic strip or bar, typically

housed inside switchgear, panel boards, and busway enclosures for local high current
power distribution. They are also used to connect high voltage equipment at electrical
switchyards, and low voltage equipment in battery banks. They are generally
uninsulated, and have sufficient stiffness to be supported in air by insulated pillars.
These features allow sufficient cooling of the conductors, and the ability to tap in at
various points without creating a new joint.
The term busbar is derived from the Latin word omnibus, which translates into English
as "for all", indicating that a busbar carries all of the currents in a particular system.

TYPES OF BUS BAR ARRANGEMENTS:

6
 a). SINGLE BUS BAR

This system is used for 132 K V substations. it is cheapest among all the other
bus bars. It is totally shut down in case of a Bus fault.

b). DOUBLE BUS BAR

7
 Main & Transfer bus
scheme

Three Bus system:

Main 1 &2 ,
Transfer/Bypass bus

This system is costlier then a single bus bar system. One bus can serve as reserve, which
is used during maintenance or fault. It is used for 220 KV substations.

8
c) . DOUBLE BUS BAR WITH TRANSFER BUS :

BUS COUPLER BY-PASS BAY FEEDER BAY GENERATORR

BAY BAY
BUS - 1

BC
Three Bus system:
BUS - 2
Main 1 &2 ,
Transfer/Bypass bus

TRANSFER BUS

GT

This system has additional flexibility for operation. We can take shut down on a
breaker without interrupting the transmission line. It is used for critical 220 KV
substations.

d )BREAKER AND HALF ARRANGEMENT :

9
 In this arrangement, three breakers are used for two circuits. It is important for
400 KV substations where higher flexibility is required. Cost is higher for this
arrangement.

The loads are automatically transferred

One &toHalf
healthy bus scheme
Breaker from faulty bus without
interruption of circuit. Here loss of 50% of Circuits can be eliminated when there is bus
bar fault or breaker fault.

Tower (structure) is a lattice structure built up by bolting /riveting/welding the

structural members of Galvanized steel that supports insulators, overhead transmission
line conductors and overhead earth wire. Structures also used for supporting flexible
bus bar insulators, equipment insulators, rigid bus bar insulators, and lightning masts
and overhead shielding mesh in substations (SS).Towers and structures are made .The
types of Towers not yet standardized and more than 35 types of towers are in practical
use.

10
OUTGOING 220KV LINE FROM THE PCHES SWITCH YARD

11
 4. EQUIPMENTS IN THE SWITCH YARD :
4.1 INSULATORS:

The flexible ACSR conductors of transmission line and substation bus bars are
supported on string insulators. The rigid tubular bus bars in SS are supported on Solid
insulators/Post insulators.

Materials used for Insulators

 Ceramic (Porcelain, Steatite)
 Glass
 Synthetic Resins.
(Glass-fiber reinforced epoxy resin rod covered by sheds made of silicon-
rubber.)
PROPERTIES OF INSULATORS:-
 High Electrical resistance of insulator material in order to avoid leakage
currents to earth.
 High Mechanical strength to with stand conductor load, wind load etc.
 It should be non porous and free from impurities and cracks.
 High ratio of puncture strength to flashover.

Three distinct types of Insulators are used in transmission systems and

substations:

1. String Insulators (Suspension or Tension) for supporting ACSR or AAAC

conductors. The string consists of several identical Ball and socket type
Disc insulators in series with end fittings on cross arm side and conductor
side.
2. a) Solid post insulators for SS apparatus and rigid tubular bus bars.
Several identical units assembled to form one Post insulator (stack).The
insulators are used in assembly of isolators, to support bus bars etc.
b) Solid core Insulators. Are used in the following applications and named
accordingly.

12
 Post Insulators for support
Shaft insulators.
Operating rod insulators.
3. Hollow Porcelain Insulators for Transformer bushings, SF6 GIS
bushings, CTs, CVTS, PTs, CBs chambers.
For DISTRIBUTION NETWORKS & SS:

 Pin Type Insulators. (for LT& HT)

 Shackle insulators:

 Stay Insulators:

The important requirement of air-insulation and porcelain insulators in EHV

substations and transmission lines are
 Creepage Distance

13
Creepage Distance: shortest distance between two conducting parts along the surface
of the insulating material.

Depends on
 Phase to ground Voltage.
 Degree of atmospheric pollution.

Degree of Pollution Recommended Creepage distance.

Clean areas 16 mm/kV (rated ph to Ph)
Moderately polluted area 20 mm/Kv
Industrial area 22 mm/kV
Heavily polluted & coastal area 25 mm/kV

4.2 CONDUCTOR AND ACCESSORIES :

Conductor consists of several strands (individual wires) wound in layers spiraled

along the length of conductor. Consecutive layers are twisted spirally in opposite
direction to provide good interlayer grip and gives strength and flexibility to the total
conductor.

Electrical Grade Aluminum wires or Al alloy wires are used for conductor for
carrying current. In the core, Galvanized Steel wires are used for reinforcement .The
core gives high tensile strength & conductor has low resistance.

14
Construction: surround a central wire; wires are wound spirally in the form of layers of
wires containing 6,12,18,24 … wires. Thus, the total number of individual strands ‘N’ in
a stranded conductor with ‘n” layers is given by
N=3n2 + 3n + 1.
Diameter of conductor= (2n+1)*d
‘d’ is diameter of strand (wire)
The conductors used are:
AAAC All-Aluminium Alloy conductor.

ACSR Aluminium conductor steel reinforced.

AACSR Aluminium alloy conductor .steel reinforced.Etc

15
The conductors are identified by their code names assigned by the manufacturer of
conductors like Moose, Zebra, dove etc.
Conductors are designated as:
Ex: 54/7/3.18.
Zebra conductor:
Aluminium strands =54 numbers
Steel strands =7
Diameter of wires = 3.18 mm

4.3 CLAMPS & CONNECTORS:

Tee-Connectors. For connecting ACSR conductor to ACSR tap conductor (dropper)

Parallel-Grove Connectors (PG clamp): For connecting two ACSR flexible conductors
in parallel.
Fixed type bus post Clamps: For supporting tubular bus on post insulators.
Pad Clamps. For Isolator to ACSR conductor connections
Spacers.
 For twin conductor bundle.
 For quadruple conductor bundle
Hardware for string insulator assembly.

16
Variants in Clamps and connections

17
4.4 CIRCUIT BREAKERS.

Circuit breakers are switching devices, design to close or open contact

members, thus closing or opening an electrical circuit under normal or abnormal
conditions.
Circuit breaker is automatic switching Device which can
 carrying normal current & switching in & out normal loads
 Interrupt short circuiting currents.
 can able to performer auto-reclose duty.

Classification of circuit breakers:

Based on LOCATION

 Indoor
 Outdoor.

Based on INTERUPTING MEDIUM

 Air break ………….. Air Break Circuit Breaker……….. (ACB)

 Air blast ……………. Air Blast Circuit Breaker …………(ABCB)
 Bulk oil……………… Bulk Oil Circuit Breaker …………(BOCB)
 Minimum oil……….. Minimum Oil Circuit Breaker ……(MOCB)
 SF6 gas insulated….. SF6 Circuit Breaker………………...(GCB)
 Vacuum……………. Vacuum Circuit Breaker………….(VCB)

18
Selection of a CB depends on :
1. Type of application
2. Rated voltage, current
3. Its Breaking capacity (fault level of the installation)
4. Auto-reclose duty Cycle.
Structural form of a Circuit Breaker (CB): depends on its type, rated voltage, type of
design, and type of operating mechanism.
 In door, metal-clad switchgear (up to 12kV): the three poles of circuit breaker
are mounted on with draw able truck.
 Outdoor switchgear (for above 33kV): the structural form of CB depends on
Rated voltage
Type of operating mechanism
Type of design
Type of interrupting medium.

Sub-assemblies of an outdoor CB:

1. Poles
2. Frame & structures
3. Operating mechanism housing
4. Control cabinet/switch cubical
5. Auxiliaries (Air compressors, receiver tank etc)

OPERATING MECHANISM:
Generally there are three types of mechanisms for EHV CBs:
1. Spring operating mechanism.
2. Pneumatic operating mechanism.
3. Hydraulic operating mechanism
4. Pneumo-spring mechanism

19
FEATURES:
SF6 gas circuit breaker has the following features.
1) superior interrupting capability:
This breaker can successfully interrupt high short circuit current with high rates
of TRV (transient recovery voltage), short line faults, capacitive current with out
generating dangerous over voltages.

2) Low operation noise:

Since the break is sealed off from the atmosphere ,there is no gas exhaust noise
during operation.

3) Simple construction & compact size :

Single break at 245KV coupled with non –exhausting gas design makes the
breaker structure simple & compact.

4) Easy installation and maintenance :

As the construction is simple, installation & inspection is very easy and since
deterioration of SF6 gas is negligible and erosion of arching contact by arching
in SF6 gas is very little , the maintenance interval is very long.

5) High safety:
Since SF6 gas is physically non –toxic and non –in flammable the breaker can be
operated safely .

245kV, type 200-SFM-40A, CGL make SF6 Gas circuit breaker:

Introduction:

These breakers are of single pressure type. Operating on puffer principle where
in, puffer cylinder and piston generate the gas flow arcing zone. This construction
shown in Fig 1.1 is very simple.

20
 The moving contact system is connected to operating mechanism. Housed in
mechanism housing. The operating mechanism uses compressed air for opening and
spring force for closing. Since compressed air is required for opening operation. The
mechanism is simple and reliable. The pole units are sealed of from atmosphere
contamination and therefore deterioration of SF6 gas and erosion of contacts is very
little.

These breakers are of single pressure type, operating on puffer principle

wherein, the gas flow on to the arcing zone is generated by puffer cylinder and piston.
The moving contact system is connected to operating mechanism, housed in mechanism
housing. The operating mechanism uses compressed air for opening and spring
charging .the spring force is used for closing. The pole units are sealed off from
atmosphere contamination and therefore deterioration of SF6 gas and erosion of
contacts is very less.

CONSTRUCTION:
GENERAL:

General construction of the breaker is illustrated in Fig1.2 . This is a single phase

auto- re closing type circuit breaker . The three phases have their won mechanism and
air reservoir inter connected electrically and pneumatically. The phases can be mounted
at any desired phase to phase clearance. A typical single pole of the breaker consists of
interrupting unit (100) supporting unit (200)and mechanism housing(300). Operating
mechanism is connected to pole unit through linkages. The electrical control units are
mounted in central phase or a separate free standing marshalling box which can be
supplied on request

INTERRUPTING UNIT :
Interrupt assembly:
The interrupter is a single pressure puffer type which consists of a puffer cylinder
(110)and a piston(112) stationary contact (106) and its assembly is suspended from the
upper side of the interrupting porcelain (114) over head conductors are connected to the
upper and lower terminal pads (101)and (116).

21
a) CLOSED POSITION :

In closed position current flow from the upper terminal (101) to lower terminal
(116) and vice versa through the stationary contact (106) , the moving contact (108),
puffer cylinder (110) and the fixed finger contacts (113).

b) OPENING OPERATION:
Opening is effected by pulling down the insulating rod (201), piston rod (111),
puffer cylinder (110),moving contact (108),moving arc contact (107), and the nozzle
(105) after some contact wiping stationary and moving arc contacts (104), (107)separate
thereby generating arc .during down ward movement the gas pressure in puffer
chamber builds up and highest pressure gas flows through nozzle and quenches the arc.

c) CLOSING OPERATION:

In closing operation , insulating rod ,(201) is pushed up and all the parts move in
the reverse direction of the opening operation. also SF6 gas is also taken into puffer
chamber .

2. SUPPORT UNIT ASSEMBLY

Support unit assembly consists of support porcelain(202) ,and insulating pull rod
(201) .this provides insulation between live parts and ground SF6 gas is filled in
containers interrupting unit and support unit at rated pressure.

3. SHAFT SEAL :

Shaft seal assembly (203) Is located at the lower flange of the supporting
porcelain to seal the gas .it consists of a spring ,brass bush Teflon and rubber
washers which ensure tight gas sealing

22
4. GAS SYSTEM:
The gas system of this breaker is illustrated in fig .2.2. each pole has its
independent gas system monitored individually by gas density switch (temperature
compensated gas pressure switch ) and pressure gauge .
the gas can be filled from valve A while valve B serves as isolating valve for
calibration of gas density switch .

5. AIR SYSTEM :

Compressed air is required for opening operation of the breaker .it is stored in 3
inter connected air receivers of capacity 70 L each , which act as local source of

compressed air for the operating mechanism .this system is provided with motor
compressor unit .the capacity of compressor is 90 L /m and sufficient to cater to
individual breaker . this governor switch operated safety valve is provided which blows
off at 17.0 to 18.0 kg/cm2 in case of over pressure . it is necessary to drain the condense
from the air reservoir once every week through the drain valve .

6. LOW PRESSURE PROTECTION :

To ensure of safety of breaker operation two types of pressure switches have
been incorporated .

1) Temperature compensated gas pressure switch :

This switch cuts off the trip coil circuit and closing circuit in case SF6 gas
pressure below the specified range due to leakage . the operating pressure is corrected
to ambient temperature these are temperature compensated pressure switches (hence
called density switches) and there are two micro switches which operate at two different
pressures .one of them is for low pressure alarm and the other is for low pressure cut
out .as soon as the alarm comes the gas must be filled to required level .

23
7. CONTROL CIRCUIT :
All control elements are mounted on a common base plate . this plate is mounted on
the mechanism housing through anti vibration mounting . So that vibration and shock
coming from housing due to breaker operation do not reach the control elements .
thermostat is providing to keep air pressure above condensation point . its setting can
be varied between 30~80 degrees centigrade

24
25
RATINGS
ANNEXURE
TECHNICAL PARTICULARS OF 220KV SF6 CIRCUIT BREAKERS
Make :CGL

1. Applicable technical standards : IEC-56/1997

2. Rated Voltage (RMS) : 245 KV
3. Rated Frequency : 50Hz
4. Number of poles per breaker : 3
5. Class (out door/indoor) : Out door
6. Rated normal current : 2500 A
7. Rated short circuit breaking current :
a) RMS value of AC component : 40 KA
b) Percentage of DC component : 50 %
c) Asymmetrical breaking current : 49 KA
( including DC component )
8. Short time current rating for 3sec (RMS) : 40KA
9. a)Rated short circuit making current (peak) : 100KA
b)Rated short circuit breaking current : 40 KA
10. Rated out of phase breaking current : 10 KA
11. Rated operating sequence : 0-0.3 sec -CO-3 MIN -CO
Operating mechanism : Motor wound spring
12. Type of closing mechanism : Spring
13. Type of tripping mechanism : Spring
14. a)Total creep age distance to ground. : 7595 mm
b) Creep age factor for the porcelains : Equal to or less than 4
c) Profile factor for the porcelains : Above 0.7
15. Rated closing voltage (closing coil voltage) : 220V DC
16. Rated opening voltage (trip coil voltage) : 220V DC
17. Rated gas pressure : 6 Kg /cm at 20 C
18. First pole to clear factor : 1.3
19.a) Rated lightning impulse withstand voltage : 1050 KVP
(to earth ,between poles and across open

26
 circuit breaker)
b) Rated one minute power withstand voltage
(RMS value) : 460KV RMS
(to earth ,between poles and across open
circuit breaker)
20. System neutral : solidly grounded
21. Design ambient temp. : 50 C
22. Rated small inductive
current breaking capacity : 1A to 12 A
23. Rated line charging current : Not less than 125Amp
24. Operating time
a) Total beak time from the instant of : Less than 3 cycles for all types of
trip coil energisation duties &
currents up to rated breaking
b) Closing time : Less than 8 cycles

25. Latching requirement : Mechanically & Electrically

trip free
26. Anti pumping device : Both mechanical and electrical
antipumping device should be
provided
27. Maximum temp. rise of circuit breaker : Ten (10 C ) deg C lower than
components the values specified in Table-4
of IS : 2516 (Part- , Sec-2)
28 . Minimum phase to phase spacing : 4500 mm

Maintenance:

To achieve the satisfactory performance, the user shell strictly adhere to the
following three aspects as per the recommendations .
1. storage and handling
2. installation testing and commissioning

27
 3. maintenance
the periodic maintenance measure comprise the following which will be elaborated
sequential
1. Visual inspection and checks
2. cleaning
3. Lubrication
4. Checking of oil, contacts and extinguishing
5. over handling

4.5 ISOLATOR AND EARTHING SWITCH INTRODUCTION :

ISOLATORS:
In sub-stations it is often desired to disconnect a part of the circuit for
maintenance or repairs of conductors, clamps, CBs etc. This is accomplished by an
Isolator (Isolating switch).Isolators are switches operated when the line in which they
are connected carry no current.
Isolator (disconnecting switch) operates under no load condition. It does not
have any specified current breaking capacity or current making capacity. Isolator is not
even used for breaking load currents. In some cases isolators are used for breaking
charging current of transmission line.
Isolators used for power systems are generally 3-pole isolator. The 3-pole
isolator have three identical poles. Each pole consists of two or three insulator posts
mounted on a fabricated support. The conducting parts are supported on the insulator
posts. The conducting parts consists of conducting copper or aluminum rod, fixed and
moving contacts. During the opening operation the conducting rod swings apart and
isolation is obtained. The simultaneous operation of three poles is obtained by
mechanical inter •locking of the three poles. Further, for all three poles, there is a
common operating mechanism.
The operating mechanism is manual plus one of the following:
1 .electrical motor mechanism
2.pneumatic mechanism

28
Further, the isolator can be provided with earthing switching when required. The
earthing switch consists of a conductor bar. When the earthing switch is to be closed,
these bars swing and connect the contact on line unit of isolator to earth.
To prevent mal-operation, the isolator is provided with the following interlockings:

Types of construction of isolator: -

- vertical break type
- Horizontal break type, either centre break or double break
Vertical pantograph type.
- Pantograph type

These are outdoor air break disconnecting switches of the gang-operated

horizontal break type with rating of 7kv and above.
Horizontal Break Centre Rotating Double Break Isolator :

In this type of construction, there are three insulator stacks per pole. The two in
each side are fixed and one at the centre is rotating type. The central insulator stack can
swing about its vertical axis through about 90deg. The fixed contacts are provided on
the top of each insulator stacks on the side. The contact bar is fixed horizontally on the
central insulator stack. In closed position, the contact shaft connects the two fixed
contacts.
The insulator are mounted on a galvanized rolled steel frame. The three poles are
interlocked by means of steel shaft. A common mechanism is provided for all three
poles.

EARTHING SWITCH: -
Earthing switch is connected between the line conductor and earth. Normally
it is open. When line is disconnected, the earthing switch is closed so as to discharge the
voltage trapped on the line. Though the line is disconnected, there is some voltage on the
line to which the capacitance between line and earth is charged. This voltage is
significant in high voltage system. Before proceeding, with the maintenance work these
voltages are discharged to earth by closing the earth switch.
Sequence of operation while opening/closing a circuit:-

29
 For taking out of service for maintenance:
1. Open circuit breaker
2. Open isolator
3. Close earth switching

While normalizing (closing the circuit)

1. Open earth switching
2. Close isolator
3. Close circuit breaker

4.6 INSTRUMENTAL TRANSFORMERS:

1. CURRENT TRANSFORMERS:
Protective relays in AC power system are connected in the secondary circuit of the
current transformers .
Current transformers are classified into two groups
1. Protective current transformers
2. Measuring current transformers

CURRENT TRANSFORMER

30
 Ratio error and phase angle errors are the important errors of these transformers.
The ratio error is very important in protective current transformers ,and phase angle
error may be less important .
Larger cores and air gaps are introduced in CT`S for fast protective relays, in order
To prevent saturation of current transformer cores during sub-transient current.

Some terms to be noted:

Accuracy class:
The class assigned to current transformers with the specified limits of ratio error
and phase angle error .
For relaying purpose the ratio error becomes important. Generally the load on the
secondary side of CT is at such a high lagging power factor that the secondary current
Is almost in phase opposition with the magnetizing current and , there fore, phase angle
error is negligible .Ratio error is very significant because the currents are high during
short circuit conditions .
%R.E. at Ip = ((Kn Is-Ip)/Ip)*100
where %R.E.=%ratio error
Ip= r.m.s. value of current in primary
Is= r.m.s. value of current in secondary
Kn=nominal ratio =rated primary current /rated secondary current

Burden on CT:
Impedance of secondary circuit expressed in ohms and power factor. It can be
expressed as apparent power and rated secondary current at specified power factor.
The circuit connected to the secondary winding is termed as `burden` of the
current transformer.
Open circuited secondary of circuit : An important aspect in CT operation is voltage
appearing across open circuited secondary normal voltage across secondary of a 15VA
CT with current of 5A,secondary voltage is 15/5=3V.

31
 However, if by mistake secondary is open circuited , the voltage across the
secondary rises to a high value .The peak value may reach some kilovolts.
Open circuiting of secondary results in zero secondary current , hence reduced back
e.m.f. the working flux zero increases and core gates saturated .the secondary e.m.f.
increases due to increased flux .
The primary gates over heated and the core also gets over heated. Voltages are
induced in the secondary by electro-magnetic induction .The peak value of the
secondary voltage on open circuit may be several times the r.m.s. value since the core is
saturated and waveform voltage is distorted .This may cause danger to personnel
working on secondary side. Therefore when primary current flowing, secondary should
never be disconnected .In bus zone protection a non linear resistor may connected
across secondary to limit the peak voltage to safe value.

32
DESCRIPTION OF CT`S:
The current transformer types IT 245 are out door, single phase post
type with oil impregnated paper insulation and hermitically sealed enclosures.
The primary winding is of eyebolt design with capacitance graded voltage
insulation. Primary currents are more than one value is obtained by providing either
primary reconnection or secondary tapping .
The core is made of high-grade electrical steel through which the required numbers
of secondary turns are wound torridly. This assembly is located in the eye of the
primary winding. The active part is located inside tank. There is more than one
secondary, to achieve various functions like metering or protection. A high voltage
porcelain insulator serves as the external insulation. One oil sight glass is provided and
section head contains the primary terminals .
A Nitrogen valve in the dome. Nitrogen gas which acts as a cushion for expansion and
contraction of oil.
The transformer is hermetically sealed to eliminate moisture absorption and oil
contamination.
OPERATION:
CT`S whose primary windings have been energized must not be open on the
secondary side. The secondary winding should either be short-circuited or closed by a
load corresponding to the rated burden indicated on the rating plate.

ESSENTIAL FEATURES:
Connection head:- The connection head contains the primary terminals
The current transformer types IT 245 are out door, single phase post type with oil
impregnated paper insulation and hermitically sealed enclosures.
The primary winding is of eyebolt design with capacitance graded voltage
insulation. Primary currents are more than one value is obtained by providing either
primary reconnection or secondary tapping .
The core is made of high-grade electrical steel through which the required numbers
of secondary turns are wound torridly. This assembly is located in the eye of the
primary winding. The active part is located inside tank. There is more than one
secondary, to achieve various functions like metering or protection. A high voltage
porcelain insulator serves as the external insulation. One oil sight glass is provided and

33
section head contains the primary terminals .One of which is brought out insulated P1
and other P2 is firmly bonded to steel body of the connection head. Necessary primary
reconnection terminals are provided. Sealing is effected by means of rubber bellows
incorporated in the head, which allows for expansion of oil. The entire arrangement is
such that the contact with the oil is avoided.

Terminal Box:

Contains secondary terminals .All terminals are easily accessible when the cover is
removed .
Arcing rings: Arcing horns can be supplied when expressly stipulated. They are
adjustable and are of shape, which avoids any polarity influence.
Oil: Since both the quality of oil and degree of dryness and dissolved gasses exert
Extraordinary effect in the reliability of CT`S, they are normally filled with oil.
Output and accuracy: The torrodial cores can give a very high power in metering and
protective cores, despite the low values chosen for the ampere turns. The instrument
security factors for metering can be kept small, while saturation factors of protective
cores can be kept high even at high out puts.

MAINTENANCE:

At suitable intervals depending on the operating conditions, check the earthing of the
tank and also clean the out side of the insulator.

SPECIFICATION FOR FEEDER CT

Nominal system voltage 220 KV

Highest system voltage 245 KV
Power frequency withstand voltage KV(RMS) 460 KV
Lightning impulse withtand voltage KV (peak) 1050 KV
No.of cores 5
Core 1 2 3 4 5

34
Rated primary current 800 800 800 800 800
Rated secondary current 1 1 1 1 1
Class of accuracy PS PS 0.2 PS PS
Output VA - - 20 VA - -
ISF - - <5 -
R ct at 75 deg C <10 <10 - <10 <10
Standard IEC 185/ IS 2705 or as per latest standards
Ith KA rms / sec 40 KA / 1 sec
I dyn 100 KA peak

2. VOLTAGE TRANSFORMERS:

Voltage transformers are used for measurement and protection. These are
necessary for voltage directional, distance protection. The primary of the voltage
transformer is connected directly to power circuit between phase and ground depending
upon rated voltage and application. The volt ampere rating of voltage transformer is
smaller.
There are two types of construction:
- electro magnetic potential transformer, in which primary and secondary are
wound in magnetic cores like usual transformer.
- Capacitor potential transformer, in which the primary voltage is applied to a series
capacitor group. The voltage across one of the capacitor is taken to auxiliary voltage
transformer. The secondary of auxiliary voltage transformer is taken for measurement
or protection.

Voltage Transformer

35
220 KV BUS PT
TYPE ELECTROMAGNETIC TYPE
SYSTEM RATED VOLTAGE 220 KV
HIGHEST SYSTEM
VOLTAGE 245 KV
RATED PRIMARY
VOLTAGE 220 KV/√3

36
Voltage Factor 1.2 continuous 1.5/30 sec
Ins Level 460/1050 KV
Secondary Winding 1 2
Measuring Protective
O/p 300 VA 100 VA
Class of acc. 0.2 without 3P
simultaneous
loading
Primary Terminals A-N
Sec. terminals 1a1 -1n 1a2-1n 2a1-2n 2a2-2n
Voltage ratio 220,000/√3 / 220,000/√3 / 220,000/√3 220,000/√3
110 110√3 / 110 / 110√3

Total creepage distance 6125 mm

SPECIFICATIONS:

The following aspects should be determined while selecting the voltage

transformer:
1) Rated primary voltage
2) Rated secondary voltage
3) Rated burden
4) Supply frequency
5) Number of phases
6) Class of accuracy
7) Insulation level, Power frequency and impulse voltage withstand.
8) Limits of dimensions, type of construction etc.
SOME IMPORTANT TERMS:
Rated transformation ratio:- The ratio of rated primary voltage to rated secondary
voltage.
Residual voltage:- Vector sum of three line to earth voltages
Residual VT:- A three phase VT or a group of three single phase residually
connected VT`s in which residual voltage appears across secondary terminals when
three phase voltages are applied to primary windings.
Ratio error:- Percentage ratio error some times called percentage voltage error is
given below
Voltage factor:- The upper limit of operating voltage is given by
Rated primary voltage* voltage factor, is specified for certain time.

37
 e.g.,1.1 continuous, 1.5 for 60 seconds ., 1.9 for 30 seconds.,
BURDEN on VT: -
Burdens are specified in volt amperes at rated secondary voltage at a particular
power factor. Let rated secondary be Vs. The ohmic impedance of burden be Zb.
Volt-ampere burden= p
Zb = Vs*VS/p
The rated burden on a VT should be less than rated burden of VT.
Connections of VTs:
There are three types of connections, V-V, star-star and star-open delta
V-V Connections:- This connections is used only for measurement and usually not
for protection.
There no path for Zero sequence voltages arising from earth faults .
Star-Star connection :- Either three separate transformers or a single three limb
transformers are used. The neutral point of the load is connected to neutral point of
secondary. The neutral point of primary is solidly earthed.
If primary neutral is not earthen, the zero sequence component of voltages
cannot flow through primary windings. Hence phase to earth voltages of system
which contain zero sequence component do not get truly transformed
Hence the earth fault on the system cannot be sensed on the secondary side of the VT

TYPES OF CONSRUCTIONS OF VT`S:

1.Electro magnetic voltage transformer , oil filled /epoxy resin encapsulated

2. Capacitor voltage transformer. (CVT)
Composite transformers used for protection and measurement are normally of full
range. Once the adjustment setting to suit a particular set of capacitors has been
determined, no further adjustments are necessary in service.
-If CVT of suitable transient performance is not available, cascade type
electromagnetic VT should be preferred.
CVT's should not give ferro - resonance and secondary over-voltages
Electro magnetic voltage transformer: -Potential transformer is similar to a
conventional transformer. The construction of PT largely depends on the rated primary
voltage. For voltages upto 3,3kv dry type transformers with varnish impregnated taped

38
windings are quite satisfactory. For higher voltages it is a practice to immerse the core
and winding in the oil. Recently windings are impregnated and encapsulated in
synthetic resins. The core of a smaller voltage transformer is usually made up of normal
T, Ur E, I, L shaped laminations when hot rolled steel is employed. For larger single
phase unit cut C core is oriented sheet steels.
The electromagnetic PTs are either indoor or outdoor. Porcelain are necessary for
outdoor PTs. the electromagnetic PT fro residual connections should have live limbs.
For voltages above 66kv.electromagnetic PTs are generally in cascade connection. They
employed number of series connected primary coils on separate cores, with coupling
coils to link primary coils so as to keep the effective leakage inductance at a low value.
Such an arrangement is conveniently housed in a porcelain enclosure.
The secondary leads should have low impedance to reduce voltage drop.

3. INTRODUCTION TO CAPACITVE VOLTAGE TRANSFORMERS:

Capacitor voltage trans formers are used for line voltmeters,
synchroscopes, protective relays, tariff meter, etc. The capacitor voltage transformers
are more economical than electro magnetic voltage transformer v* hen the nominal
voltage increases above G6kv.
DESCRIPTION:

The CVT consists if capacitive potential divider and an inductive medium

voltage circuit. The inductive part is immersed in mineral oil and hermetically sealed
with an air cushion inside a steel tank. One, two or three capacitor units are mounted
on the steel tank and are used as capacitive potential divider provided the current taken
by the burden is negligible compared with the current passing through the series
connected capacitors. The reactor connected m series with the burden is adjusted to
such a value that at supply frequency it resonates with the sum of two capacitors. This
eliminates any errors in the system.
CVT as coup ting capacitor for carrier current applications: - The carrier
current equipment is connected to the power line via coupling capacitor. The coupling
voltage divider can be used for coupling purpose.
Choice of capacitance value of CVT: - The range of frequency over which the
accuracy has to be maintained governs the maximum output from

39
The permissible rated output may be derived from the expression:

W=K(C1+C2) Vi*VWc Where W = output in va

K = constant depending on frequency, losses, etc ;
Cl = capacitance of primary voltage capacitor in farads i
C2 = capacitance of intermediate voltage capacitor in farad;
Vi = intermediate voltage in volts ;
Oc = phase angle error change in minutes per Hz.
From the above expression that, for a given accuracy over a given frequency range, the
rated output is proportional to the total capacitance at a fixed tapping point voltage. On
the other hand, when the capacitance values are fixed by other considerations, for
example, carrier current requirements, the rated output may depend entirely on the
permissible phase-angle error change per Hz.

40
Consider a single diagram of CVT and its equivalent circuit referred to primary voltage
Vp. At normal power frequency C and L are in resonance, therefore, offer zero
impedance. Therefore, the CVT behaves like conventional VT. However, this resonance
is at a particular frequency. At other frequencies, Ic and IL do not get cancelled and the
reactive component present introduces phase angle error in measurement. This error
depends on the power factor of burden. The phase angle error changes with frequency.
However, choice of frequency depends upon whether the capacitor is used as coupling
capacitor for carrier channel or not.
Ferro-resonance in CVT: - The excitation impedance Ze and equivalent C of voltage
divider may form a resonant circuit which may oscillate at lower frequency than 50Hz.
If such a circuit is introduced to an impulse voltage due to switching,
transient voltage oscillations of variable frequency do occur. These can pass through a
range of frequencies due to nonlinear nature of inductance of auxiliary VT.
Good design of CVT will not exhibit ferro - resonance for resistive burdens.
Auxiliary VT's should have large core so as to maintain flux density at a low value to
prevent saturation.
Application of CVT for protective relaying: -
-For capacitor type voltage transformer used for residual connection, accuracy class 10
is generally preferred.

220 KV CVT
STANDARD IEC - 186 or latest standards
RATED VOLTAGE A-N 220 /√3 KV
HIGHEST SYSTEM VOLTAGE A-N 245/√3 KV
INSULATION LEVEL 460 / 1050 KV
VOLTAGE FACTOR 1.2 CONTINUOUS 1.5/30 SEC
FREQUENCY 50 HZ
NOMINAL INTERMEDIATE VOLTAGE 20/√3 KV
HF CAPACITANCE 4400 PF +10% -5%
C1 PRIMARY CAPACITANCE 4840 PF +10% -5%
C2 SECONDARY CAPACITANCE 48400 PF +10% -5%
TOTAL OUT PUT SIMULTANEOUS 300 VA
OUTPUT MAXIMUM 750 VA
NO. OF SECONDARY CORES 3
VOLTAGE RATIO 220000/√3 / 110/√3 / 110/√3 / 110-110/√3
WINDING 1a-1n 2a-2n 3a1-3a2-3n
voltage 110/√3 110/√3 110-110/√3
burden 50 200 50
class 0.2 0.5 3P

41
 Insulation class A

4.7 METAL OXIDE SURGE ARRESTERS

Metal oxide surge arrester also known as zinc oxide surge arresters are well accepted as
voltage clippers for effective protection against over voltages.

GENERAL: Metal oxide surge arresters protect the costly out door electrical equipment
from over voltages caused by atmospheric disturbances due to lightning and internal
disturbances due to switching surges

CONSTRUCTION: The assembly consists of Metal Oxide elements with contact plates
between discs and held rigidly by a tie rod assembly. the striking aspect of this arrester is its
simplicity of construction.
1) THERMAL DISSIPATION :A system of silicone bumpers on each contact plates provides
thermal dissipation of heat generated in the elements for Temporary Over Voltages and
Transmission Line Discharges in addition to ruggedzed support to prevent damage in
shipping.

The heat generated in the Zinc Oxide elements is conducted through the contact plates to
silicone bumpers which are slug fit to the bushing and then through the bushing to the
atmosphere .

2): PRESSURE RELEASE ARRANGEMENT

The pressure relief device is a standard feature in all the station class arresters. Under
normal conditions the pressure relief diaphragm seals the internal components from the
atmosphere and open out to relieve the internal pressure generated, in the remote event of
arrester failure, which causes sustained short circuit the high pressure gases generated inside
the Arrester are directed and vented through the exhaust ports thus transferring the internal
arc to outside, avoiding violent explosion of the arrester housing to safeguard adjacent
equipment and personnel

Directing the ionized gases is important to prevent damage from flashover or adjacent
arresters, transformer bushings and bus supports .

42
43
44
PRINCIPAL OF OPERATION:
The excellent non-linear characteristics of the Zinc Oxide element keeps the
current at normal line to ground voltage in micro amperes, mainly being determined by the
dielectric constant and cross sectional area .how ever , if a certain voltage stress is exceeded ,
the device the “Cross Over “ and exhibits a very high nonlinear characteristic.

Metal Oxide voltage limiters are the new type of surge suppressors having exceptionally high
non-linear Volt-ampere characteristics with high energy absorption capability. A large
change in current through the resistor will result in a relatively small change in the voltage
across the resistor .An increase in current from a few micro amps to 10,000A-9 orders of
magnitude-increases the voltage by only 75%. The arrester designed by using Metal Oxide
elements, approximates more closely to an ideal constant voltage device

Optimum arrester characteristics are obtained by the use of Metal Oxide elements.

1) This new arrester draws very little current at the system voltage
2) Enters in to conduction at a voltage close to arrester rating
3) Holds the voltage with little change during the conduction period of surge current
4) Ceases to conduct at very nearly the same voltage at which conduction has started

Metal Oxide elements are made from Zinc Oxide with other metal oxide additions by
forming into discs at high pressure and sintered in high temperature kilns in accordance with
a pre-determined programme . The resulting resistor element is an extremely dense
polycrystalline ceramic material with highly complex micro structure. The structure of the
sintered body is a matrix of highly conductive Zinc Oxide grains and highly resistive
intergranular boundary regions and depletion layers resulting in a highly non-linear
characteristics . Micro structure is the vehicle through which all the electrical characteristics
are manifested .The elements have an insulating collar to avoid external flash over and the
parallel phases are metallized for uniform current distribution

The Varistor characteristics are evaluated by non –operating methods for varistors used in
electronic component industry and under operating and stressing conditions for varistors
used in surge arresters .

45
FEATURES:
a. HIGHER DUTY CAPABILITY:
The ZnO arrester has no gaps and so the discharge is smooth and effective
There being no follow current the Metal Oxide arrester conducts only that current required
to reduce the surge voltage to the arrester protective level and therefore dissipates only the
energies associated with the surges. Hence , the arrester operates cooler and can absorb
higher energy surges in rapid succession.

b. BETTER PROTECTIVE LEVEL :

MOSA has predictable stable and precise operating characteristics . Due to its high non-
linearity the protective levels are low
MOSA has quick response to surge voltages of the order of nano seconds . Hence it absorbs
the incoming surge without any time delay .As there are no gaps there is no need to consider
the volt –time-gap spark over characteristics.

c. SUPERIOR PERFORMANCE AGAINST POLLUTION :

METOVAR Arrester has high tolerance to the effects of external housing contamination due
to the self capacitance of the discs and staggered petticoat design of the housing .

d. EXCELLENT ENERGY DISSIPATION CAPABILITY:

METOVAR Arresters can be used with confidence for severe switching conditions for shunt
capacitor banks and cable circuits.

e. HIGH SURGE STABILITY: OBLUM`S METOVAR Metal Oxide arresters are highly stable
and are not affected by repeated surges due to lightning and switching(transmission line
discharges.

f. THERMAL STABILITY:
METOVAR Arresters have excellent thermal stability for high energy surges , external
pollution and temporary over voltages due to liberal design and have very low losses at
operating voltages.

46
 5.TURBINE IN POWER HOUSE :

5.1 TURBINE:
A turbine is a device that harnesses the kinetic energy of some fluid - such as
water, steam, air, or combustion gases - and turns this into the rotational motion of the
device itself. These devices are generally used in electrical generation, engines, and
propulsion systems and are classified as a type of engine.

5.2 TYPES OF HYDRO TURBINES:

There are two main types of hydro turbines: impulse and reaction. The type of
hydropower turbine selected for a project is based on the height of standing water
referred to as "head" and the flow, or volume of water, at the site. Other deciding
factors include how deep the turbine must be set, efficiency, and cost.

1.IMPULSE TURBINE:

1.1. PELTON
1.2. CROSS FLOW

2.REACTION TURBINE:

2.1. PROPELLER

2.2. FRANCIS
2.3. KINECTIC
Here in the Pulichintala project we use the propeller type turbine which
comes under the reaction turbine, and again in the propeller type turbine is classified in
to Bulb turbine, Tube turbine, Straflo and Kaplan turbine.
In this power house we use KAPLAN TURBINE with the rated speed of 125
RPM

47
 KAPLAN TURBINE IN THE POWER HOUSE
5.3.NAME PLATE DETAILS OF THE HYDRO TURBINE USED:

5.4.KAPLAN TURBINE:

The Kaplan turbine is a propeller-type water turbine which has adjustable

blades. It was developed in 1913 by Austrian professor Viktor Kaplan, who combined
automatically adjusted propeller blades with automatically adjusted wicket gates to
achieve efficiency over a wide range of flow and water level.
The Kaplan turbine was an evolution of the Francis turbine. Its invention allowed
efficient power production in low-head applications which was not possible with Francis
turbines. The head ranges from 10 to 70 metres (33 to 230 ft) and the output ranges
from 5 to 200 MW. Runner diameters are between 2 and 11 metres (6 ft 7 in and 36 ft
1 in). Turbines rotate at a constant rate, which varies from facility to facility. That rate
ranges from as low as 54.5 rpm (Albeni Falls Dam) to 450 rpm.[2]
Kaplan turbines are now widely used throughout the world in high-flow, low-head
power production.

5.4.1OPERATION OF TURBINE:
The Kaplan turbine is an inward flow reaction turbine, which means that the
working fluid changes pressure as it moves through the turbine and gives up its energy.
Power is recovered from both the hydrostatic head and from the kinetic energy of the
flowing water. The design combines features of radial and axial turbines.

48
The inlet is a scroll-shaped tube that wraps around the turbine's wicket gate. Water is
directed tangentially through the wicket gate and spirals on to a propeller shaped
runner, causing it to spin.
The outlet is a specially shaped draft tube that helps decelerate the water and
recover kinetic energy.
The turbine does not need to be at the lowest point of water flow as long as the draft
tube remains full of water. A higher turbine location, however, increases the suction
that is imparted on the turbine blades by the draft tube. The resulting pressure drop
may lead to cavitation.
Variable geometry of the wicket gate and turbine blades allow efficient operation for a
range of flow conditions. Kaplan turbine efficiencies are typically over 90%, but may be
lower in very low head applications.[3]
Current areas of research include computational fluid dynamics (CFD) driven
efficiency improvements and new designs that raise survival rates of fish passing
through.
Because the propeller blades are rotated on high-pressure hydraulic oil bearings, a
critical element of Kaplan design is to maintain a positive seal to prevent emission of oil
into the waterway. Discharge of oil into rivers is not desirable because of the waste of
resources and resulting ecological damage.

49
 KAPLAN TURBINE OVER VIEW

6. EARTHING (GROUNDING):

Earthing is provided for:

 Safety of personal.
 Prevent or minimize damage to equipment as a result of flow of heavy fault
currents.
 Improve reliability of power system.

The Earthing is broadly divided as:

50
 1. SYSTEM EARTHING:
2. EQUIPMENT EARTHING. (SAFETY GROUNDING)
SYSTEM EARTHING:
Connection between neutral of transformer/ generator to earth.
EQUIPMENT EARTHING:
Connecting all non-current carrying metal parts of electrical equipment (other than
current carrying conductors) to earth.

Earth resistance of earth pits/electrodes shall not exceed the following

limits:
Power Generating stations 05 ohms
EHT sub-stations 1.0 Ω
33 kV SS 2.0 Ω
D/t structures 5.0 Ω
Tower foot resistance 10.0 Ω
To keep the Earth resistance must be kept as low as possible in order to achieve safe
step potential, touch potential, an earth mat shall be buried at the above depths below
ground and the mat shall be provided with grounding rods at suitable points.

All Non-current carrying parts at substation (structures, Marshalling boxes, mechanism

boxes etc) shall be connected to this mat so as to ensure that under fault condition none
of these parts are at a higher potential than the ground potential, thus avoiding electric
shock to personal.
PHOTOGRAPHS AT THE PROJECT:

51
THE GATE OF THE TURBINE WHICH CLOSES THE TURBINE BLADES

PRESSURE RECEIVER

52
TAIL RACE OF THE PCHES
Water which is are used in the turbine will be out from the tail race. Such water will be send
as shown in picture.

POWER TRANSFORMER OF POWER HOUSE

This power transformer can step up the voltage level from 11KV[GENERATED VOLTAGE]
to the 220KV[REQUIRED VOLTAGE].

53
 CONCLUSION

This mini project EHV Switch yard is constructed in such a way that even ,
one can understand about the working and principle of switch gear components used in
EHV switch yard. This also explains the types of bus bar arrangement. And here in the
power house we also observe the excellence of working condition of machines and
motors.
Last but not least without switch gear there is no proper usage of electricity.

54