INTRODUCTION OF PROTECTIVE RELAYS
The protective relay is device that connect conne ct 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 co ndition 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 bea m 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 u per 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 RELAY Buchholz 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 deco mposed so, lightly bubble and gas produce. That gas moves towards the the conservator from main 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 who le 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 o f 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 select the transformer portion 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 11 3.7 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 pu t 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 con nect cemented. it is a H-type basement
Then i visit the second transformer, it is made o f 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. 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 provides the oil level of the tank .its oil level was w as 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. d irection. It gives the trip single at the time of reverse direction power from normal direction of power. The combination of non directional directional and directional element make the relay that operates when current flow in a specific directions. The directional element is used in e lectromagnetic 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 an d 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 time of reverse current, current, if reverse current increased from adjust 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 ARRESTERS Lightning 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 abno rmal 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 con nected 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. co ver.
There are bushing used on steel cover. Then steel cover is completely with immersed oil.
In normal condition the primary voltage remains constant, so v olt 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 an d PT are used at 132kv grid station Khanewal on 11kv feeder,132kv lines.
Circuit breaker
I observe circuit breaker of grid grid station. It has three types of circuit circuit breakers oil, SF6 and vacuum.
First I observe the SF6 SF6 circuit 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 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 b reaking 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. nozz le. There is also side vent that provides gas into interrupter chamber.
In normally condition both contacts closed with o ther 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 kep t 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.
