ABOUT THE FIRM

Punjab State Power Corporation Ltd.

(POWERCOM)

Starting with the modest installed capacity of 62 MW, the PSEB (from which

POWERCOM unbundled)grew up by leaps and bounds. Envisaged with an

aim to produce power required for multitude of uses in state of

Punjab, POWERCOM generated 37222 million units during 2008-09 , which is more than 2006-07 by 2238 Million Units resulting of 6.40% increase in two years. It has its thermal power

plants situated in Ropar, Bathinda and Lehra Mohabbat and

hydel projects in form of Ranjit Sagar Dam, Shanan Power

House, Anandpur Sahib Hydel project, Mukerian Hydel Project

Stage 1 and U.B.D.C. (Upper Bari Doab Canal) Hydro Electric

Power House. The Corporation has an ambitious plan to add sufficient generating capacity in the State in order to bridge the gap between demand and supply. A beginning was made in this regard by improving the performance of the existing units.

ABOUT THE

TRAINING I had my training in 66

..TRAINING REPORT SUBMITTED BY-: PARDEEP DIXIT [Type the abstract of the document here. The abstract is typically a short summary of the contents of the document. Type the abstract of the document here. The abstract is typically a short summary of the contents of the document.] [Type the author name] [Pick the date]

KV Substation located in sector 71, Mohali. Commissioned in 2-

2-2011, this substation has incoming from 220 KV Substation

located in Mohali phase 1. It basically has a step down

distribution 66/11 KV transformer and is responsible for supply

to 11 kv substation located in 3B1 Mohali, Mattur village, 3B2

and Phase7.Training basically included of being part of work

culture in substation, information about all the parts present in

substation, their uses and intricacies involved.From these

substations the power reaches our home through distribution

transformers.

SUBSTATION

A substation is a part of an electrical generation,

transmission, and

distribution system.

Substations

transform voltage

from high to low, or

the reverse, or

perform any of

several other

important functions.

Electric power may flow through several substations

between generating plant and consumer, and its voltage

may change in several steps.

A substation that has a step-up transformer increases the

voltage while decreasing the current, while a step-down

transformer decreases the voltage while increasing the

current for domestic and commercial distribution.

NEED OF SUBSTATIONS

1. For efficient and reliable power distribution

2. To improve power factor whenever needed

3. It is practically unfeasible to control and keep

an eye on the power supply of large region, so

we need substations controlling smaller regions.

4. It houses vrios protection devices such as

lightening arresters,circuit breakers,isolators. 5. With number of substations ,fault isolation,detection

and correction becomes convenient

VARIOUS PARTS PRESENT IN 66 KV

SUBSTATION

DISTRIBUTION TRANSFORMER 66/11 KV, 20 MVA

by IMP

CURRENT TRANSFORMER

VOLTAGE TRANSFORMER

SULPHUR HEXAFLOURIDE CIRCUIT BREAKERS

ISOLATOR

RELAYS(STATIC AND ELECTROMAGENTIC)

LIGHTENING ARRESTERS

BATTERY ROOM

TRANSFORMER

It is a static electric device which transforms electric

energy from one circuit to another through magnetic

medium without any change in frequency. Because a

transformer works on the principle of electromagnetic induction,

it must be used with

an input source

voltage that varies in

amplitude.

Transformer can be

Step Up or Step

Down depending

on requirement at

the receiving end.

On the basis of

location these are of

two types-:

1. Power Transformer-

These are designed to have maximum efficiency at

full load. These are basically used at the generating

end such as various power generating plants. These

are Step Up transformers. Voltage is stepped up to

minimize losses occurring in the long transmission

line given by

H = I^2*R*T

2. Distribution Transformer-

These are designed to have maximum efficiency at

half of a load. These are widely used in the

substations to step down the high voltage coming

from power transformers present in power plants.

On the basis of construction these are of following

type

1. Core Type-

These have L or U type laminations.

Material used- silicon steel

Joints of different laminations are alternative.

Alternative joints are to provide path to flux so that

flux continues to pass through laminations.

Laminations are insulated to reduce eddy current

losses.

Thickness of L type laminations- 0.35 mm

2. Shell Type-

In this, laminations shapes are of E and I types.

Thickness of laminations 0.35 mm

Laminations are placed inverted to each other to

provide continuous flux flow

Used in remote and hilly areas

Parts of a Transformer-:

CORE Transformers have silicon steel cores for flow of magnetic field.

This keeps the field more concentrated around the wires, so that

the transformer is more compact. The core of a power

transformer must be designed so that it does not reach magnetic

saturation. Carefully designed gaps are sometimes placed in the

magnetic path to help prevent saturation.

Practical transformer cores are always

made of many stamped pieces of thin

steel. The high resistance between layers

reduces eddy currents in the cores that

waste power by heating the core. These

are common in power and audio circuits.

A typical laminated core is made from E-

shaped and I-shaped pieces, leading to the

name "EI transformer".

WINDINGS

The winding material depends on the application. Small power

and signal transformers are wound with insulated solid copper

wire, often enameled. Larger power transformers may be wound

with wire, copper or aluminum rectangular conductors, or strip

conductors for very heavy currents. Windings on both primary

and secondary of a power transformer may have taps to allow

adjustment of the voltage ratio; taps may be connected to

automatic on-load tap changer switchgear for voltage regulation

of distribution circuits.

INSULATION

The conductor material must have

insulation to ensure the current

travels around the core, and not

through a turn-to-turn short-

circuit. In power transformers, the

voltage difference between parts

of the primary and secondary windings can be quite large.

Layers of insulation are inserted between layers of windings to

prevent arcing, and the transformer is immersed in transformer

oil that provides further insulation and acts as a cooling medium.

COOLING

High-power or high-voltage transformers are bathed in

transformer oil - a highly-refined mineral oil that is stable at

high temperatures. Large transformers to be used indoors must

use a non-flammable liquid. Today, nontoxic, stable silicone-

based oils or fluorinated hydrocarbons may be used, where the

expense of a fire-resistant liquid offsets additional building cost

for a transformer vault.

The oil cools the transformer, and

provides part of the electrical

insulation between internal live

parts. It has to be stable at high

temperatures so that a small short

or arc will not cause a breakdown

or fire. To improve cooling of

large power transformers, the oil-filled tank may have radiators

through which the oil circulates by natural convection. Very

large or high-power transformers (with capacities of millions of

watts) may have cooling fans, oil pumps. Oil transformers ar

equipped with Buchholz relays.

BUCHHOLZ RRELAY

Buchholz relay is a safety device mounted on oil-filled power

transformers and reactors, equipped with an external overhead

oil reservoir called a conservator. On a slow accumulation of

gas, due perhaps to slight overload, gas produced by

decomposition of insulating oil accumulates in the top of the

relay and forces the oil level down. A float switch in the relay is

used to initiate an alarm signal.If an arc forms, gas accumulation

is rapid, and oil flows rapidly into the conservator. This flow of

oil operates a switch attached to a vane located in the path of the

moving oil. This switch normally will operate a circuit breaker

to isolate the apparatus before the fault causes additional

damage. Buchholz relays have

a test port to allow the accumulated gas to be withdrawn for

testing. Flammable gas found in the relay indicates some

internal fault such as overheating or arcing, whereas air found in

the relay may only indicate low oil level or a leak .

OTHER PARTS

Transformer also has a temperature measuring devices in it. It

measures temperature of both primary and secondary winding

and of transformer oil. This proves of great use especially in

summer season.

It also has a motor for circulation of transformer oil. It

automates the oil level in transformer.

With time,it turns pink due to

moisture and hass to be replaced manually.

INSTRUMENT

TRANSFO

RMERS

Instrument transformers (ITs) are designed to

transform voltage or current from the high values in the transmission and distribution systems to the low values that can be utilized by low voltage metering devices. Depending on the requirements for those applications, the IT design and construction can be quite different. Generally, the metering ITs require high accuracy in the range of normal operating voltage and current. During a disturbance, such as system fault or overvoltage

transients, the output of the IT is used by a protective relay to initiate an appropriate action (open or close a breaker, reconfigure

the system, etc.) to sort the disturbance and protect the rest of the power system. Instrument transformers are the most common and economic way to detect a disturbance. CURRENT TRANSFORMER

Current transformer (CT) is

used for measurement of electric

currents. When current in a

circuit is too high to directly

apply to measuring instruments, a current transformer produces

a reduced current accurately proportional to the current in the

circuit, which can be conveniently connected to measuring and

recording instruments. A current transformer also isolates the

measuring instruments from what may be very high voltage in

the monitored circuit. Current transformer has a primary

winding, a magnetic core, and a secondary winding. A primary

objective of current transformer design is to ensure that the

primary and secondary circuits are efficiently coupled, so that

the secondary current bears an accurate relationship to the

primary current.

The most common design of CT consists of a length of wire

wrapped many times around a silicon steel ring passed over the

circuit being measured. The CT's primary circuit therefore

consists of a single 'turn' of conductor, with a secondary of many

hundreds of turns. The primary winding may be a permanent

part of the current transformer, with a heavy copper bar to carry

current through the magnetic core. Shapes and sizes can vary

depending on the end user or switchgear manufacturer.

From construction point of view, there are two types of

current transformers which are commonly used in laboratories

and panels. These are:-

1. Clamp-On or Clip-On

2. Bar Type

1. Clamp-On or Clip-On:- It is a Current Transformer in which the core can be opened

with the help of clamp and the conductor can be inserted in the

core. A single conductor acts as a primary and secondary is

wound on the core. An ammeter connected across the secondary

winding of the transformer which measure the current flowing to

the conductor directly. It is a portable instrument and generally

used in laboratories for testing purposes.

2. Bar-Type:- A Bar-Type current transformer has a circular ring type core

over which secondary is wound. An ammeter is connected

across the secondary. When a bar conductor or bus bar is

inserted through it, the ammeter measure current flowing

through bar conductor directly.

These are generally used with

instruments placed on panels or used

with the protective relays.

POTENTIAL TRANSFORMER

The potential transformer are

basically step-down transformers.

The connections of voltmeter when used in conjuction with the

potential transformer for measurement of high A.C. voltages.

The voltage to be measured is applied across the primary

winding which has a large no. of turns is coupled magnetically

to the primary winding. Turn ratio is so adjusted that the

secondary voltage is 110V when full rated primary voltage is

applied to primary.

Potential transformers are used to operate voltmeter, the

potential coils of wattmeter and relays from high voltage lines.

The design of potential transformer is quite similar to that of

power transformer. But the loading capacity of a potential

transformer is very small in comparison to that of power

transformer. The loading of a potential transformer some time

is only a few volt amperes. These transformers are made shell

type because this condition develops a high degree of accuracy.

For medium voltages i.e. upto 6.6 KV the potential transformer

are usually of dry type, between 6.6 KV to 1.1 KV they may be

either dry or oil immersed but for voltage more than 11 KV they

always oil immersed type. An out of door type oil immersed

voltage transformer having ratio 66000/110.

The working of a potential transformer is essentially the

same as that of a P.T. is very small and consequently the

exciting currents almost of the same order as that of secondary

current. Whereas in power transformers exciting current is very

small fraction of secondary load current.

USE OF C.T. AND P.T. FOR POWER

MEASUREMENT

For measurement of power or energy in a high voltage

power system, both C.T. and P.T. are used. P.T. is used to step

down the system voltage and C.T. is used to step down the

system current up to the required level. P.T. is connected in

parallel and C.T. is connected in series. The potential coil of

wattmeter is connected across the secondary of P.T. and

current coil is connected across the secondary of C.T.

Wattmeter or Energy meter so connected measure the power

or energy of the circuit directly.

ISOLATORS

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. Often the isolation switch is not intended for

normal control of the circuit and is only used for isolation.

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.

CIRCUIT BREAKERS

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.

The circuit breaker must detect a fault condition; in low-voltage

circuit breakers this is usually done within the breaker enclosure.

Circuit breakers for large currents or high voltages are usually

arranged with pilot devices to sense a fault current and to

operate the trip opening mechanism. The trip solenoid that

releases the latch is usually energized by a separate battery,

although some high-voltage circuit breakers are self-contained

with current transformers, protection relays, and an internal

control power source.

Once a fault is detected, contacts within the circuit breaker must

open to interrupt the circuit; some mechanically-stored energy

(using something such as springs or compressed air) contained

within the breaker is used to separate the contacts, although

some of the energy required may be obtained from the fault

current itself. Small circuit breakers may be manually operated;

larger units have solenoids to trip the mechanism, and electric

motors to restore energy to the springs.

The circuit breaker contacts must carry the load current without

excessive heating, and must also withstand the heat of the arc

produced when interrupting (opening) the circuit. Contacts are

made of copper or copper alloys, silver alloys, and other highly

conductive materials. Service life of the contacts is limited by

the erosion of contact material due to arcing while interrupting

the current. Miniature and molded case circuit breakers are

usually discarded when the contacts have worn, but power

circuit breakers and high-voltage circuit breakers have

replaceable contacts.

When a current is interrupted, an arc is generated. This arc must

be contained, cooled, and extinguished in a controlled way, so

that the gap between the contacts can again withstand the

voltage in the circuit. Different circuit breakers use vacuum, air,

insulating gas, or oil as the medium in which the arc forms.

SF6 CIRCUIT BREAKERS

. These breakers are available for indoor or outdoor applications,

the latter being in the form of breaker poles housed in ceramic

insulators mounted on a structure.

Current interruption in a high-voltage circuit-breaker is obtained

by separating two contacts in a medium, such as SF6, having

excellent dielectric and arc quenching properties. After contact

separation, current is carried through an arc and is interrupted

when this arc is cooled by a gas blast of sufficient intensity.

Gas blast applied on the arc must be able to cool it rapidly so

that gas temperature between the contacts is reduced from

20,000 K to less than 2000 K in a few hundred microseconds, so

that it is able to withstand the transient recovery voltage that is

applied across the contacts after current interruption. Sulphur

hexafluoride is generally used in present high-voltage circuit-

breakers (of rated voltage higher than 52 kV).

Into the 1980s, the pressure necessary to blast the arc was

generated mostly by gas heating using arc energy. It is now

possible to use low energy spring-loaded mechanisms to drive

high-voltage circuit-breakers up to 800 kV.

DISADVANTAGES OF SF6 CIRCUIT BREAKERS

1. SF6 is the most potent greenhouse gas that the Intergovernmental Panel on Climate Change has evaluated. It has a global warming potential that is 23,900 times worse than CO2.

2. When an arc is formed in SF6 gas small quantities of lower order gases are formed. Some of these byproducts are toxic and can cause irritation to eyes and respiratory system.

3. SF6 is heavier than air so care must be taken when entering low confined spaces due to the risk of oxygen displacement

LIGHTENING ARRESTER

The lightning arresters provide protection against atmospheric

lightening. A lightning arrester is a protective device, which

conducts the high voltage surges on the power system to the

ground.

It consists of a spark gap in series with a non-linear resistor. One

end of the diverter is connected to the terminal of the equipment

to be protected and the other end is effectively grounded. The

length of the gap is so set that normal voltage is not enough to

cause an arc but a dangerously high voltage will break down the

air insulation and form an arc. The property of the non-linear

resistance is that its resistance increases as the voltage (or

current) increases and vice-versa.

The action of the lightning arrester or surge diverter is as under:

(i) Under normal operation, the lightning arrester is off the line

i.e. it conducts no current to earth or the gap is non-conducting

(ii) On the occurrence of over voltage, the air insulation across

the gap breaks down and an arc is formed providing a low

resistance path for the surge to the ground. In this way, the

excess charge on the line due to the surge is harmlessly

conducted through the arrester to the ground instead of being

sent back over the line.After the surge is over, the resistor offers

high resistance to make the gap non-conducting.

JUMPER and TOWER

In a straight run line, one terminal pole is provided after

very 1km so as to

facilitate sagging.

Sagging of a line means

The short length of

conductor used to

connect line conductor

on one side of terminal

pole to the line

conductor on the other side of terminal poleis known as

jumper.

A jumper is made of same material and has same current

carrying capacity as that of line conductor. With a suitable

clamp for HV lines, jumpers are arranged in such a way

that under maximum deflection condition, there is

maximum clearance of 0.3m between line jumpers and

other metallic parts.

COUPLING CAPACITOR AND WAVE

TRAP

These instruments are not used for electrical supply.

Coupling capacitor is used for communication. It takes place

conversion between two Sub Stations. Wave Trap is also for

communication. It receives the sound below 20 hertz frequency

and left the sound above 20 hertz frequency. This reaches the

sound one Sub-Station to another Sub-Station and

communication takes place.

CAPACITOR BANKS

Shunt capacitor banks are used to improve the quality of the

electrical supply and the efficient operation of the power system.

Studies show that a flat voltage profile on the system can

significantly reduce line losses. Shunt capacitor banks are

relatively inexpensive and can be easily installed anywhere on

the network. Shunt capacitor banks (SCB) are mainly installed

to provide capacitive reactive compensation/power factor

correction. The use of SCBs has increased because they are

relatively inexpensive,easy and quick to install and can be

deployed virtually anywhere in the network. Its installationhas

other beneficial effects on the system such as: improvement of

the voltage at the load, better voltage regulation (if they were

adequately designed), reduction of losses and reduction or

postponement of investments in transmission.The main

disadvantage of SCB is that its reactive power output is

proportional to the square of the voltage and consequently when

the voltage is low and the system need them most, they are the

least efficient.

RELAYS

A Relay is an electrically operated switch. Many relays use an

electromagnet to operate a switching mechanism mechanically,

but other operating principles are also used. Relays are used to

protect electrical circuits from overload or faults; in modern

electric power systems these functions are performed by digital

instruments still called "protective relays".

ELECTROMAGENTIC RELAYS

The core of the electromagnetic relay is an electromagnet,

formed by winding a coil around an iron core. When the coil is

energized by passing current through it, the core in turn becomes

magnetized, attracting a pivoting iron armature. As the armature

pivots, it operates one or more sets of contacts, thus affecting the

circuit. When the magnetic charge is lost, the armature and

contacts are released. Demagnetization can cause a leap of

voltage across the coil, damaging other components of the

device when turned off. Therefore, the electromagnetic relay

usually makes use of a diode to restrict the flow of the charge,

with the cathode connected at the most positive end of the

coil.The electromagnetic relay is capable of controlling an

output of higher power than the input.

STATIC RELAY

The conventional relay type of electromagnet relays can be

replaced by static relays which essentially consist of electronic

circuitry. Static relays are superior to electro-magnetic relays.

1. The moving parts and the contacts are largely eliminated. The only moving element in a static relay is the final tripping contact.

2. More precise and high speed operation.

Static relay consists of DC supply required for energizing the

circuitry of the static relay. This is obtained from DC batteries.

It then compares the actual quantity with the pre-set quantity.

For example in an over-current relay it will compare the actual

current supplied by CT with the pre-determined set current over

which tripping is required. By using the gate circuits conditions

of operation of relays are set and relay can only be operated

when requisite conditions are satisfied. The actual tripping of

relay can be achieved by firing the SCR i.e. silicon controlled

rectifier.

DIFFERENTIAL RELAY

Another common form of protection for high voltage apparatus such as transformers and power lines is current

differential. This type of protection works on the basic theory of Kirchhoff's current law which states that the sum of the currents entering a node will equal zero. It is important to note the direction of the currents as well as the magnitude, as they are vectors. It requires a set of current transformers (smaller transformers that transform currents down to a level which can be measured) at each end of the power line, or each side of the transformer. The current protection relay then compares the currents and calculates the difference between the two.

As an example, a power line from one substation to another will have a current differential relay at both substations which communicate with each other. In a healthy condition, the relay at substation A may read 500 amps (power exporting) and substation B will read 500 amps (power importing). If a path to earth or ground develops there will be a surge of current. As supply grids are generally well interconnected the fault in the previous example will be fed from both ends of the power line. The relay at substation A will see a massive increase in current and will continue to export. Substation B will also see a massive increase in current, however it will now start to export as well. In turn the protection relay will see the currents travelling in opposite directions (180 degrees phase shift) and instead of cancelling each other out to give a summation of zero it will see a large value of current. The relays will trip the associated circuit breakers. This type of protection is called unit protection, as it only

protects what is between the current transformers. It is important to note that generally the higher the currents in the lines the larger the differential current required for the relay to see it as a fault.