Summer Training

Report

132 KV GRID
SUB STATIONS
BEER
(HISAR)
PREPARED BY
DEEPAK
ROLL NO. 200110900014
GOVT. POLYTECHNIC SIRSA
 SUB STATION

GENERAL BACKGROUND

A substation forms an important part of transmission and distribution system

of electric power system. An electric substation consists of a number of
incoming and outgoing circuits connected to common bus bar systems. Bus
bars are conducting to which a number of incoming and outgoing circuits
are connected. These components are connected in a definite sequence such
that a circuit can be switched off during operation by manual command and
also automatically during abnormal conditions such as short-circuits.

A substation receives electric power from generating station via incoming

transmission lines and delivers electric power via the outgoing transmission
lines. Substations form important links between the generating stations,
transmission systems, distribution systems and the load points. A substation
thus provides a point for controlling the flow of power.

FUNCTIONS OF A SUB STATION

An electricity supply undertaking generally aims at the following points:

 Continuous electric power supply to all the consumers at all times.

 Maximum security of supply.

 Shortest possible fault-duration.

 Optimum efficiency of plants and the network.

 Supply of electric power within targeted frequency limits, (49.5Hz and

50.5 Hz).

 Supply of electric power within specified voltage limits.

 Supply of electric energy to the consumers at the lowest cost.

Classification of substation:

1. Generating substation

2. Grid substation (132kv)

3. Distribution substation (33kv, 11kv)

Details of 132KV BEER (HISAR)Sub-Station :-

132 KV BEER(HISAR) SUB-STATION AT A GLANCE

A) TECHNICAL DETAILS:

Voltage Level: 132 KV

Total Land Area: 04 Acre
Switchyard Area with control room 04 Acre

B) PARTICULARS OF EXISTING 132 KV SIDE:

No. of 132 kv line feeders 02

No of Bays 07
No. of T/F 03
No. of Bus Coupler 01

C) PARTICULARS OF EXISTING 132 KV SIDE:

No. of 132 KV line feeders : 02
No of bays : 07
No of T/ : 01

132 KV BEER (HISAR) SUB STATION

At present two lines of 132 KV are in operating condition. Following are the
major equipments used at 132 KV grid substations.
 Equipmets:

1. LIGHTENING ARRESTER

Lightning Arrester is the apparatus commonly used to protect sub-station

equipment against lightening strokes on the lines entering the sub-station. It
diverts the transient over voltage surges to earth and protect the substation
equipment from lightning and switching over-voltage surges.

The most important and costly equipment in a substation is the transformer

and the normal practice is to install a lightning arrester as near the
transformer as possible. At Beer (Hisar) substation Metal-Oxide type
arrester (zinc-oxide arrestor) is installed.

2. Isolators
Isolator is a switching device which can be opened or closed only under no
current or no load condition. It provides isolation of the circuit for the
purpose of maintenance

Isolators are disconnecting switches and are used for disconnecting of the
circuit under no load conditions. Isolator provides a visible air gap isolation
of equipment and feeder sections for safe examination, maintenance and
repair. It is capable of carrying normal current and short circuit current for a
specified time. The various types of isolators are as follow.

 Horizontal center break

 Double Break
 Pantograph
 Vertical single break

The earth switch of isolator is a mechanical switching device for providing

safety earthing during maintenance. It is capable of withstanding short
circuit current for a specified time.

ISOLATORS AT BEER(HISAR) SUBSTATION

In BEER (HISAR) Substation the isolators used are single break and double
break isolators. All the isolators used in the substation are manually and
electrically operated.
Ratings of Isolator
Make : SIEMENS
Rated voltage : 145 KV motorized type

Electric motor : 1HP,1385 rpm, 415 v,1.95 A

Reduction gear ratio : 20:1
Opening and Closing time : 10 to 12 sec approx.
Auxillary contacts : 8 NO +8 NC,10 A

3. Circuit Breakers
Circuit Breaker is a device capable of making, breaking an
electrical circuit under normal and abnormal conditions such as
short circuits.

Why do we have Circuit Breakers?

• To switch Transmission Lines, Transformers, Shunt Reactors,

Capacitor Banks etc.

• To close/reclose an open circuit

 • And of course the most important to clear a fault to protect
equipment, and human life!

We can say circuit breaker generally use to break the current through circuit
under any condition whether it is load or no load condition. If we want to
open an isolator than firstly we have to open the circuit breaker first because
isolator opens at no load condition.

The Breakers used in BEER (HISAR) sub-station are of SF 6

type

Circuit Breakers both of 132 KV ratings used at Beer (Hisar) Sub Station
are of SF6 type. SF6 used here for its arc extinction property.

Which reduces the production of arc almost at the time of opening or closing
of the breaker
Ratings of Circuit Breakers (132 KV)

Make : SIEMENS

Rated voltage : 145 kV

Lightening impulse : 650 kV

Withstand voltage

Short Ckt. Breaking current : 40 kA

Short time withstand : 40 kA , 3 Sec.

Current and duration

Rated Power freq. : 275 kV

Withstand voltage

Rated normal current : 3150 A

Line charging : 50 A
Breaking current

Impulse weight of SF6 gas : 8.1 kg

Frequency : 50 Hz

3. Transformers

 A transformer is a static device, which consists of two or more

 Stationery electric circuits interlinked by a common magnetic
circuit
 For the purpose of transferring electrical energy between them.
 This transfer of energy takes place without change in frequency.
 A transformer may be used to step-up or step-down a voltage.
 A transformer may be a two winding transformer
 or inter-connected transformer(auto-transformer).

APPLICATION OF TRANSFORMERS
Transformers are used in number of applications:
 To change the level of voltage and current in electric power
system.
 As impedance matching device for maximum power transfer in
low power-power electronic and control circuits.
 As a coupling device.
 To isolate one circuit from another, since primary and secondary
are not interconnected.
 To measure voltage and currents; these are known as instrument
transformers.

Transformers are extensively used in Ac power system for the following

reasons:

 Electric energy can be generated at most economic level (11KV-

33KV)

 Stepping of generated voltage to high voltage, extra high voltage

EHV(voltage above 230 KV), or to even ultra high voltage UHV
(750 KV and above ) to suit the power transmission requirement
to minimize losses and increase transmission capacity of lines .

 The transmission voltage is stepped down in many stages for

distribution and utilization of domestic, commercial and industrial
consumers.

Ratings of transformer 132kV 40/50MVA

No of transformer : 1

132/33 kv : 1

Make : ECE

Type : Two windings

No. of phase : 3

Rated Voltage : HV 132kV

 LV 33 kV

Rated line Current : HV 174.95

LV699.82

Frequency : 50Hz

Insulation Level : HV L1( 550/AC 230)

: Hvn&LVN L170/AC 70
: LV(170/AC70)

Core and oil mass : 45800kg

Tank and fitting mass : 17350kg

Mass of oil : 16350kg

Total weight : 79500kg

Volume of oil : 18400 l

Ratings of transformer 132kV 10/16MVA

No of transformer : 2

Make : HHE and ECE

Rated Voltage : HV 132kV

LV 11kV

Rated Current : HV 54.7A

LV 656A
 No. of Phase : 3

Frequency : 50Hz

Temperature Rise : 50/55

Type of cooling : ON

Weight of core and winding : 45800kg

Weight of oil : 16350kg

Total weight : 79500kg

Oil quantity : 18400L

4. CURRENT TRANSFORMERS

Current Transformers are used for reducing/stepping down a.c. current from
higher value to low value for measurement / control. The current
transformers may be either of bushing type or wound type. The bushing
types are normally accommodated within the breaker on the transformer
bushings and the wound types are invariably separately mounted. The
location of current transformer with respect to associated circuit breaker has
an important bearing upon the protection scheme.

The Current Transformers in BEER (HISAR) Sub-Station:

Detailed particulars of 132 KV Current Transformers as used at
BEER(HISAR) are mentioned below:
Ratings of Current Transformer
Make : SCT Ltd
Rated voltage : 145 kv
Rated thermal current : 125% of rated current
Short time current : 40 A (rms) for 1 sec
Lightning impulse : 1050 kv
Withstand voltage
Oil quantity : 200 Lt

5. POTENTIAL TRANSFORMERS

Potential transformer may be defined as an instrument transformer for the

transformation of voltage from a higher value to lower value. Potential
Transformers are used for measurement and protection.. Voltage
transformers are necessary for voltage, directional, distance protection. The
primary of voltage transformer is connected directly to power circuit
between phase and ground depending upon rated voltage and application.
The volt-ampere rating of voltage transformers is lesser as compared with
that of power transformers.

Coupling Capacitor Voltage Transformer serves as a combined voltage

transformer and coupling capacitor and is most commonly used these days.

Ratings of PT :-

Make : Mehru
Freq : 50 hz
Insulation level : 460kv/1050kvp
Ratio : 220/√3kv/110√3 v

6. CAPACITOR VOLTAGE TRANSFORMERS (CVT)

Capacitor voltage transformers are used for line voltmeters, protective, tariff
meter, etc. The capacitor voltage transformer is more economical an
electromagnetic voltage transformer when the nominal system voltage
increase above 66 KV. The carrier current equipment can be connected via
the capacitor of the Capacitor Voltage Transformers. Thereby there is no
need of separate coupling capacitors.
Capacitor type voltage transformer is used for voltages 66 KV and above. At
such voltage cost of electromagnetic type potential transformers tends to be
too high. The capacitors connected in series act like potential dividers
provided the current taken by the burden is negligible compared with the
current passing through the series connected capacitors. However, the
burden current becomes relatively larger and ratio error and also phase error
is introduced. Tuning carries out compensation. The reactor connected in
series with the burden is adjusted to such a value that at supply frequency it
resonates with voltage divider. Generally high voltage capacitors are
enclosed in porcelain housing. A large metal sheet box at the base encloses
the tuning coil, intermediate transformer.
C1 : Primary Capacitance
C2 : Secondary Capacitance
G : HF Protection Device (Adjustable air gap)
Tr : Intermediate Transformer
L : Compensating Choke
Zd : Damping Device
F : Protection Device (Varistors 2 no.s in series)
NHF : HF Terminal for Carrier Communication
f : HRC Fuse (6 A)

When terminal NHF not in use for HF transmission it must be connected to

earth as supplied NHF is connected to earth.

7. Relays :-
Relay works as a protective device during abnormal condition. As every
machine has its own a rating or current capacity. When machine goes above
its normal capacity it comes under the abnormal condition. As when it
operates at abnormal condition so there are the chances of causing any type
of trouble that resulting into the machine failiure . So we have an equipment
relay which senses the abnormal conditions and break the circuit. So we can
say that relay is like a fuse which breaks the circuit at abnormal condition.

Classification of relays
1. Based on actuating quantities :
 a) Current relay

b) Voltage relay

c) Frequency relay

2. Based on logic protection for fault condition

a) Earth fault

b) Over current

c) Under voltage

d) Differential

3. Based on time characterstics

a) Definite time

b) IDMT

4.Based on its construction

a) Machenical

b) Electromagnetic

c) Digital

8.Role of Battery at Substation

Battery is heart of substation. In spite of using highly advanced
protection switchgears, if we fail to keep d.c. battery healthy then
we can’t avoid the failure of operation of substation.

Proper maintaince is the key to dependable battery operation.

Choosing a battery of sufficient capacity helps insure its long life.
A battery should be selected with ampere-hour(capacity sufficient
to carry electric load).

a) For 2 132 kv --- 220V,200AH

b) For 66kv – 220KV,100AH

Details :

Sp. Gravity of acid : Dry

No. of cells : 107
Voltage per cell : 2.05V
Temp. : 27C
Make : NED
Current during charging : 20A
 BUS BARS
The incoming circuits and outgoing circuits are connected to the bus bars.
The lines of one voltage level are connected to one three phase bus bar of
that voltage level. The bus bars carry the main power and are reliable. The
functional requirements of a bus bar system vary depending upon the type of
a particular substation. The main functions of bus bar system are:

1. These carry normal currents and overload currents continuously with

temperature rise within specified limits.

2. These withstand normal system voltage; specified transient over voltage

without flashover.

3. These withstand mechanical stresses due to wind, icing, short-circuits etc.

without damage.

4. These provide low resistance path for current flow.

The bus bar system is very important aspect in the substation design as it
directly affects the entire substation design, the location of equipment, and
operation of substation during normal, emergency and post fault conditions,
maintenance and also the substation cost.

Bus Schemes
Single Bus Scheme:

 Simplest and cheapest bus bar scheme

 Maintenance and extensions of bus bars are not possible without
shutdown of the substation.
 Operation & maintenance of bus bar is easy.
 Single Bus with Sectionaliser:

 Similar to the single bus scheme except the sectionalising breaker or

isolator.
 By keeping the sectionaliser open one section can be in service and
the other can be taken for maintenance or extension.
 If a bus section breaker is provided bus bar protection can detect fault
on any section and trip the breakers connected to that section and
isolate it.

Single main & transfer scheme:

 Individual CB can be taken out for maintenance on-load at a time.

 The transfer bus coupler acts as the breaker for the circuit under by
pass.
 Individual circuits have a bypass isolator to connect to the transfer bus
and this isolator will be closed during bypass operation of that
particular circuit.

Double bus scheme:

 Most commonly used bus scheme.
 Normally load will be distributed on both the buses and the bus
coupler will be kept closed.
 For maintenance & extension of any one of the buses the entire load
will be transferred to the other bus.
 On load transfer of a circuit from one bus to the other bus is possible
through bus isolators provided the bus coupler is closed and thereby
two buses are at the same potential.
 On load bypassing of any circuit for breaker maintenance is not
possible.

Double main with by-pass isolator:

 This bus arrangement provides the facilities of a double bus

arrangement & a main and transfer bus arrangement.
 The bus to which the transfer bus isolator is connected can be used as
a transfer bus also.
 During the time a circuit is under bypass, the bus coupler will act as
the breaker for the bypassed circuit.

Double Main & Transfer Scheme:

  In this bus scheme, in addition to the main buses there will be a
separate transfer bus also.
 Since separate transfer bus is available there will be no need of
transferring the load from one bus to the other bus unlike in a double
main cum transfer bus arrangement.
 Other features are similar to the one described in double bus cum
transfer bus arrangement.

Double bus with 1 & ½ breaker scheme:

 In this layout, two circuit have three breakers, the middle breaker ties
the two circuits and hence is called the tie breaker.
 The combination of three breakers is called a diameter.
 Parallel feeders from the same source should not be connected to the
same diameter.
  One great advantage of breaker and half scheme is that even both the
buses are out of service , power can be transferred from feeder to
another.

Double bus with double breaker scheme:

 This arrangement is very expensive one and hence followed in very

important circuit only.
 In this arrangement breaker maintenance for each circuit is possible.

Ring/Mesh bus scheme:

 This arrangement is very popular.

 As long as the mesh is closed load has two sources of supply and any
circuit breaker can be taken out of service without affecting the
supply.
 Extension of mesh station is almost impossible.
 No bus bar protection required.