INTRODUCTION OF PROTECTIVE RELAYS

The protective relay is device that connect between main circuit and circuit breaker.

It gives the trip signle to circuit breaker for disconnect the supply path during

abnormelity effect.

All type of relays used for short circuits.They supplied by CTs and PTs.Failuras in the

system are indicated by changes in current in voltages.For every tupes of falt and some

differance in these quantites each relay designed to recognise differance and oprate in

response to it.

The diffrence may be in term of magnitude,frequency ,phase angel ,rate of

change ,harmonic,wave shape duration of condition the relay fault current and its

trip coil energized and trip signal to circuit breaker to disconnect the supply from supply

source to load current.

It has main three components such as sencing element ,comparison ,and controll element

the sencing element sence the actuating quantity and gives the response.

The comparing element compare the actuating quantity with setting value of relay.The

control element compleat the opration of during the changes

of contol quantity at pick up of relay.

The circuit breaker connenct in line series and primary of city also connect on line before

load circuit.The secondary winding of city and relay oprating winding are connected

with each other.The AC trip circuit is also used for trip signal.

132 KV LINES PROTECTION

DISTANCE AND OVER CURRENT Relays used on 132kv lines

The rated frequancy of these relays is 60 cycle per second.

The rated voltage are 125 voltage.

The CT ratio also similar of 11kv feeders.

DISTANCE RELAY Distance relay works on voltage and current ratio.It has two coils.

One coil energizes from CT and second coil energizes from PT.In falt

conditon.Wheare impedance of line less than adjusted value of relay

impedance.Then torque produce and relay operate.

CONSTRUCTION It consist horizental beam.The beam is povit in middle of lower side.

They are two electomagnetic under balance beam

One electromagnetic or coil is called oprating coil and other is called

restraning coil.

Oprating coil is energized from CT and resterning coil is energized from

PT.

There are also two connects held uper side in middle of beam.There are

two fixed connect from front of beam connects.These connects relates with

. trip circuit.

There are two armature held in the lower left and right side. The armature

coils of both side are not closed at no load. They are placed in up and down.

WORKING

The relays consist of two main parts directional and non direction element.

When fault occur then fault current passes through the current coils. Then

Flux produce in the lower core of directional element.So, flux will also

Produce in the upper core due to current passes through voltage coil.

So as a result of both fluxs.The torque will be produced on the spindle.

The spindles consist of moving contacts and rotating disk. Under condition of

torque spindle moves and moving contacts closed with fixed contacts after

covered some distance.

After completeing that process the lower and uper cores of non directional

element will be automatically energized.So, due to resultant flux the spindle

of non-directional element will rotates.The rotation will complete after some

time and fix contact closed with moving contacts and trip signal provides to

trip circuit.

In this method the motion or working of non directional element can be

control with help of directional element. The directional element works first

and then non directional element.

The relay works at the time of reverse current.If reverse current increased

from adjust value.

BUCHHOLZ’S RELAYBuchholz relay only used for immersed oil transformer. It provides the protection against

Internal fault of transformer. That relay connected between transformer tank and

conservator.

When fault occur in the transformer then heat produce so, as a result gases produce.

If fault current is low than relay will provides the signal to alarm circuit. If fault current is

high than relay provides the signal to breaker circuit.

So circuit breaker disconnected the supply that connected with a transformer.

CONSTRUCTION It consists of domed type oil tight container.

There are two floats and two mercury switch in relay container.

In fault condition. These floats inverse or actuate the mercury switch and

gives the signal to alarm and tripping circuit.

That relay internally completed with oil.

These floats are held in oil and made of aluminum. Every float has a counter

weight that was made of mild steel.

WORKING When lightly fault occur in transformer then oil will be decomposed so,

lightly bubble and gas produce. That gas moves towards the conservator

from main tank.

During passes through relay the gas stored in the relay housing. so oil level in

relay becomes low.

Then first float that held internally upper side moves down due his counter

weight effect and mercury switch tilt so, the contacts of alarm circuit shorted

with each other. In this way alarm on and provides the fault information.

When heavy fault occur in transformer so, a large amount of gas will be

produced and for that risen whole oil of tank will be transfer to conservator.

So, the balence of lower float will be disturb.

VALVE TYPE ARRESTER

CONSTRUCTION

Valve type arrester used at 132 kv grid station Khanewal.

the external body of this of arrester is made of ceramic.

It consist of resistance discs set.

There is a gaps in series between these resistance discs or valve.

This resistance made of flat discs. That material is also called

Silicon carbide ceramic. This resistance separate with each other

With help of mica ring. This material has property to provide high

Resistance to power frequency voltage.

IT provide low resistance to voltage surg. One end is connected

with line and other connected with earth or either end is earthed.

this type of arrester is maximum used for transformer protection.

this arrester held hear transformer and both side of transformer,

for both side protection. This arrester used for transformer protection

for lightning or surges.

WORKING

It provides very high resistance path to normal voltage but provides

low resistance path between line and earth during high voltage surges.

It earthed high voltage surges of line.

In result there is produce non blowing discharge in special discs

Capillaries and then goes to earth.

When arrester discharge the whole surge then arrester return to

the initial position.

In normal voltage condition, there is a high insulation strength

Between scarp gaps points with help of air provide high insulation

Between gaps and points. So current could not pass through the arrester.

When high voltage surge reached at upper terminal that connected with line,

So the insulation strength between spark gaps becomes zero so current

Passes through these gaps and goes to earth.

So it works as a switch at time of high voltage surges.

The loads can not longer that used to connect with earth.

TYPES

1) SECONDRY TYPE VALVE ARRESTER

These arresters used for medium voltage equipment protection.

2) DISTRIBUTION TYPES VALVE ARRESTER

These used for 22kv lines and sub station.

3) LINE TYPE VALVE ARRESTER

These arrester used for 66kv voltage and also used for higher voltage.

4) STATION TYPE VALVE ARRESTER

These types of arrester used for high degree protection,

And generating station, sub station these used for 220kv or higher voltage.

ADVANTAGES

These are cheep of its initial cost.

These are reliable and stable.

There are very strong.

They used for high voltages.

They have running cost.

There are very fast in line work.

They have maintenance but have only cleaning.

DISADVANTAGES

These types of arrester are not used to check the steep fronted.

The efficiency can be damage due to inter of moisture in the enclosure.

TRANSFORMER I vist the whole grid station of 132kv khanewal

First i select the transformer portion for four month traning

The grid station has four transformer

Three tranformers are using for consumers load and industrial load

But one transformer for khanewal Railway.

first of all i observe the first transformer. It was made in 1993 from china.

It has 20/26 MVA capacity with out fan 20 MVA and 26 MVA with fan.

It is step down transformer

It is a three phase transformer.

It has delta to star connection means its input winding is in delta connection and out

put winding in star connection

It has 132/11kv voltage rating. It takes 132kv in put voltage and provides the

11 kv voltage from out put

It current rating is 113.7/1305A.In put current 113.7 and out put current is

1305 ampere

I see the in puts and out puts these are properly connected with

in put supply and out put supply.

It observe the whole transformer externally the bushing connections

were properly connected, no external fault transformer was damaged

the basement was made with connect cemented. it is a H-type basement

Then i visit the second transformer, it is made of Asia Sweden

It is capacity 5/6.25 MVA

It has 132/66 kv voltage rating

It is also step down transformer

It was made in 1962

It has different method of cooling. It has oil natural, air natural and

air force cooling. oil natural cooling means oil that is used in transformer

provides cooling. In air natural the air of atmosphere is used for cooling. For

this purpose radiator tubes are used.

It is three phase and its connections are also in delta/star

It has rising temperature of winding are this rating is 45 degree.

It is oil rising temperature is 40 degree at this rating

During visit of this transformer i check the slice gel, it was containing in the

breather. Its colors was blue

The slice gel used for absorb the moisture of air

After this i visit the third transformer .It is made by siemens of Pakistan.

Its capacity is 20/26 Moa

It was properly working

It is also three transformer and its connection in delta/star

I see the conservator that was connected with tank with help of bushels

relay. I check the oil level of tank due to oil gauge. The oil was matching wither

the colored part. It means that was cools

I check transformer that was provides correct reading. It show the temperature

of oil.

I check the values they were properly tied .they used for oil filling

draining and sampling.

I check oil gauge, it is a simple scale and pointer ,that provides the oil

level of the tank .its oil level was correct.

I check radiator tubes, there was no leakage.

I check the cooling fans that were connected under

the radiator tubes. there was no physical fault in the fans.

In these three transformers, two are using for provides supply to 11kv line.

they get the supply from main bulbar, where all incoming and upcoming

lines are connected the 11kvline provides supply the different areas feeders.

These feeders are used for industrial load

Third transformer is connected between 11kv line to 66kv. the railway

transformer also connected with 66kv line.

The fourth transformer is used for railway load. The railway transformer was used for

railway loads. Its capacity is 66/25MVA.

11KV FEEDER PROTECTION The over current and earth fault relays are used on 11kv feeders.

The CTs ratio on 11kv feeders 400/5A.

EARTH FAULT AND OVER CURRENT RELAY

That relay is also called direction over current relay. This form of protection

is depend on current direction. It gives the trip single at the time of reverse

direction power from normal direction of power. The combination of non directional

and directional element make the relay that operates when current flow in a

specific directions. The directional element is used in electromagnetic

over current relay for make the electromagnetic over current directional relay.

directional power relays, directional over current relay and directional earth fault

relay are include in directional relays categories. During matching of directional feature

the current coil is connected with CT and voltage coil is connected with PT secondary

side.

WORKING

The relay consistent of two main parts directional element and non directional

element.

When fault occur then fault current passes through the current coil.

Then flux produce in the lower core of directional element. So, flux will also

produced

in the upper core due to current passes through voltage coil.

So as a result of both fluxes, the torque will be produce on the spindle consistence of

Moving.

contacts and rotating disk. Under condition of torque spindle moves and moving contacts

close with fixed contacts after covered some distance.

After completing that process the lower and upper cores of non directional element

will be

automatically energized. So, due to resultant flux the spindle of non directional element

will rotates. The rotation will complete after some time and fixed contacts closed with

moving contacts and trip single provides to trip circuit.

In this method the motion or working of non directional element can be control with

help of

directional element the directional element works first and then non directional

element.

The relay work at the time of reverse current, if reverse current increased from adjust

value.

TRANSFORMER PROTECTION

Differential relays is used with transformer that are help at 132kv grid station

Khanewal.

over current relays are also used with transformer.

These relays works on 50 cycle per second

supply. But another relay that is the part of transformer is called buchholz relay.

INTRODUCTION OF LIGHTING ARRESTERSLightning arrester is a safety device that is used to

connect the in coming high voltage surges to the earth lightning arrester provides

the low impedance and easy path to high voltage surges and direct to the earth.

It provides the resistance path for current in abnormal condition because during

high terminal voltages it provide low resistance, but low terminal voltages it has

high resistance.

When high voltage surge reached at lightning arrester, then insulation of air breakdown

in the gap and arc produced.

so, low impedance path becomes between line and earth.

so, surges goes to earth. It works as a switch.

As surges diverts to earth then surge divert becomes non positive and disconnect the path

of surges between line and earth.

The lightning arrester also has a non linear resistor that is used for current limited

purpose.

The arrester used for medium voltage, 22kv, 66kv, 220kv.The arrester used for

Transmission protection as a wire used above transmission. This wire continually used

as with as transmission.

POTENTIAL VOLTAGE TRANSFORMER

INTRODUCTION:

The transformer that is used to increased voltage range of volt meter is called potential

voltage transformer. The PT is used to measure high voltage from a low range volt meter

PT is similar to power transformer. Due to work PT is step down transformer.

Normally PT is a shell type transformer. Its construction of two windings similar to

power transformer accept its power rating is very small. It has many metric tons weight.

CONSTRUCTION AND WORKING

It has two windings, primary and secondary winding.

The primary winding is connected parallel with in put voltage. The secondary

winding is free

with supply in put. The volt meter connected parallel to secondary winding. The

winding also earthed.

The load is connected to secondary winding side.

During the construction, proper turn ratio, low leakage reluctance ,low voltage drop

should

properly decided.

The both winding are in concern, for reduce the leakage reluctance.

In place of insulation, the cotton tap and vanished cambric.

The solid fiber separator are used between coils.

The high voltage condition, the PT is consist of oil immersed, but in low voltage

the PT completely sealed with compound.

There is high insulated provided between primary and secondary winding because

these winding

should be a design for high voltage.

The circular shield coil used for winding to detect the electrical stress.

The low voltage coil is wounded over paper core, and high voltage coil also assemble

under that core.

the complete assembly is sealed in oil and coil assembly keep held in a cover.

There are bushing used on steel cover. Then steel cover is completely with immersed

oil.

In normal condition the primary voltage remains constant, so volt meter can not show

reading.

The secondary winding connected volt meter, relay contacts etc.

In abnormal condition the primary winding voltage changes, so voltages across volt

meter change,

and it indicates these changes. The change of voltage effect on relay plunger contacts

and relay contacts close with each other and relay gives trip single to circuit breaker.

C.T AND P.T

The both connection of PT and CT is called instrument transformer. The CT and PT

are used at 132kv grid station Khanewal on 11kv feeder,132kv lines.

Circuit breaker I observe circuit breaker of grid station. It has three types of circuit

breakers oil, SF6 and vacuum.

First I observe the SF6 circuit breaker. there are number of C.B.The

name of circuit breaker shows that circuit breaker combine the SF6 gas

sulpher hexafluoride gas for are extinction.

In normal condition is fixed and moving contract are tough with each

other and circuit breaker is in closed position,and current will be flow

from supply to circuit breaker has hollow moving and fixed contact in

abnormal condition.

The SF6 circuit breaker in 132kv grid station has 1600A capacity .

It has rated voltage 145kv.

The 1600A capacity of C.B means that it can handled the current of

1600A without disconnect the supply it can easily handled 1600A

current will be increase from rated capacity e.g. 1600A it will tripped

or disconnect the supply that is used for any circuit.

Its voltage rating also shows that C.B can works maximum 145kv .but

as for as voltage will increase the C.B will be opened its fixed and

moving contact.

Its has rated frequency 50/cycle .

Its efficency will be maximum at voltage that has 50/cycle frequency.

It has total break time at rated breaking contect is three cycle. Its

means that when the fault will held the circuit breaker will

disconnected supply after completing three cycle from its maximum

rated voltage.

Its rated gas pressur is 5Kg/cm at 20 c. it means that gas has 20 c

temperature and 5Kg/cm pressure in this C.B.

It is made of Mitsubishi electric corporation japan.

It was made 13/2/2000.

Its date energization was 30/10/2001 date of energization means that

C.B was used for protection of circuit for abnormal condition of

supply.

I also observe other C.B that was made of siemens.

Its date of energization was 16/5/2002.

Its rated voltage is 145Kv.

It has also similar frequency rating that is 50c/s.

Its normal current is 200 A.

Its total mass is 1500 Kg.

I visit other C.B. it is made of siemens.

Its date of energization was 16/5/2002.

Its rated voltage is 145Kv.

It has also similar frequency rating that is 50c/s.

Its normal current is 200 A.

Its total mass is 1500 Kg.

COSTRUCTON

Its construction contains of interrupter unit and gas system.

Interrupter unit:

This unit contains of fixed and moving contacts. The blast shield is

used for control the arc displacement and hot gases. The moving

contacts are in form of hollow nozzle. There is also side vent that

provides gas into interrupter chamber.

In normally condition both contacts closed with other and at fault

moving contacts separate from fix contact then arc will produced.

The gas system:

The gas use in circuit breaker is very costly. It reconditioned and

Reclaimed after each operation of C.B. the gas is stored in high

pressure chamber at 16 atmosphere but gas pressure in low

pressure side is 3 atmosphere the safety provide around gas

system for leakage of gas. The temperature is kept 20 c. a heater

backed with thermostat at 16 c is provide in high pressure to

prevent of gas in high chamber at low temperature.

Working:

In normal condition fixed contacts and moving contacts are in

closed position on tough with each other and current can flow

from supply to circuit.

When fault occurs then due to arc pressure the contacts separate to

each other.

The arc shifted from main contacts to arcing contacts. There is a

layer of copper tungsten arc resistance on the surface of arcing and

main contacts. The SF6 gas is provided between contacts from

reservoir with the help of valve that opened with pressure. The

SF6 gas molecule absorb the electron become negative ions

because this gas high electro negative.