device no

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Device No. Relay Title

1 Master Element

2 Time delay starting and closing relay

3 Checking or interlocking relay

4 Master contactor

5 Stopping Device

6 Starting Circuit Breaker

7 Anode Circuit Breaker

8 Control Power Disconnecing Device

9 Reversing Device10 Unit Sequence switch

11 Reserved for future application

12 Over - speed Device

13 Centrifugal Speed Switch

14 Under Speed Device

15 Speed or Frequency Matching Device

16 For Future applications

17 Shunting or Discharge Switch

18 Accelerating or Decelerating device

19 Starting to running transition Contractor

20 Electrical operated valve

20BD20 BL

20BP

20 CH

20 D

20 EP

20IS

20 MA

20 R

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20 RF

20S

20TT

20 VT

20 ac

20 ao

20 bc20 bo

20 to

20tc

21 Distance Relay

22 Equalizer Circuit Breaker

23 Temperature Control Device


25 Synchronizing or synchronism check Device

26 Apparaus Thermal Device

26F

26O

26 W

27 Under Voltage Relay

27/50

27/59


29 Isolating Contactor

30 Annuniciator Relay

31 Separate excitation relay

32 Directional power relay (reverse power relay)

33 Position Switch

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34 Motor operated sequence switch

35 Brush operating or slip ring short circuiting device

36 Polarity device

37 Under current or under power relay

38 Bearing protective Device

38M1

38M2

38P1

38P2

38C1

38C2

38L1

38L2

38H1

38H2

39 Mechanical condition monitor

39VB

39SF

40 Field Failure Relay

41 Field Circuit Breaker

42 Running Circuit Breaker

43 Manual transfer or Selector Device

44 Unit Sequence strating relay

45 Atmospheric condition monitor

45HA

45SM

45FR

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46 Reverse phase or phase balance current relay

47

48 Incomplete sequence relay

48L

49 Machine or transformer thermal relay

50

50BF

50G

50N

50/51VR

51 AC time over current relay

51G

51LR

51N

52 AC circuit breaker

52a52b

52aa

52bb

52LC

52LS

53 Exciter or DC generator relay

54 Reserved for future application

55 Power factor relay

56 Field application relay

Phase sequence voltage relay (Phase reversal voltagerelay)

Instantaneous over current or rate of rise relay (High setphase over current relay)

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57 Short-circuited or grounding device

58 Power rectifier misfire relay

59 Over voltage relay

59N59 G / 27TN

60 Voltage or current balance relay

60FL


62 Time delay stopping and opening relay

63 Liquid or gas pressure swich

63MT

63TC

64 Ground protective relay

64G

64N

64R

65 Governor

66 Notching or Jogging device

67 AC directional over current relay

67P

67N

68 Blocking relay

69 Permissive control device

70 Electrical operated rheostat

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71 Level switch

71SB

71SO

71ST

71L

71H

72 DC circit Breaker

73 Load resistor contactor

74 Alarm relay or trip circuit supervision relay

75 Position changing mechanism

76 DC over current relay

77 Pulse transmitter

78 Phase angle measuring, or out of step protection relay

79 Auto reclosing relay

80 Flow switch

80AR

80AM

80LO

80SO

80W

81 Frequency relay

82 DC reclosing relay

83 Automatic selective control or transfer relay

84 Operating mechanism

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85 Carrier or pilot wire receiver relay

85PLCC

85TP

86 Locking out relay

86E

87 Differentional protection relay

87B

87BFP

87CD

87G

87G(SP)

87M

87N

87T

87TEED

87TG

88 Auxiliary motor or motor generator

8888C

88CA

88F

88FR

88FE

88FSC

88FSH

88FM

88FMC

88L88P

88LO

88PSO

88PSU

88PW

89 Line switch

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90 Regulating device

91 Voltage directional relay

92 Voltage and power directional relay

93 Field changing contractor

94 Tripping or trip free relay

95 Generator back up protection impedance relay.

96 Auto loading relay

97 Trip circuit supervision relay

Note:- Device Number 95 to 99 used for specific applications on individual in

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Definition and Function

An indicating device such as a control switch, float switch etc.

A device generally controled by device No. 1

A device used to place and hold a equioment out of function.

A device whose principle function is to connect a machine to its source of starting voltage

Circuit breaker used in the anode circuits of power rectifier

A device used for the purpose of reversing functions

A speed switch which functions on over speed

A device serves to open or to close a shunting circuit.

Blow Down ValveBlock Valve

By Pass Valve

Check Valve

Discharge Valve

Electro pneumatic instrumentation

Isolation Valve

Manifold Valve

Pressurizing Valve

A device whose function is to give a desired amount of time delay before or after any pointof operation in switching sequence.

A device, which operates in response to the position of a number of other devices or to anumber of predetermined conditions in a equipment

A disconnecting device such as a pull out fuse, MCCB/ MCB used for the purpose ofconnecting and disconnecting a control circuit

A device used to change the sequence in which unit may be placed in and out of service inmultiple unit equipments

A slip-frequency relay or any device operates at appoximately synchronous speed ofmachine

A speed switch which functions when the speed of the machine falls below a predeterminedvalue.

A device functions to match and hold the speed or the frequency of a machine or of a

system equal to that of another machine or system.

A device used to close or to cause the closing of circuits, which are used to increase ordecrease the speed of a machine.

A device which operates to initiate or cause the automatic transfer of a machine from thestarting to the running power connection

A solenoid or motor operated valve, which is used in vacuum, air gas, oil, water or similarlines. Following suffix letters are used to designate applications:

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Relief Valve

Suction Valve

Throttling Control Valve

Vent Valve

Open only when valve is fully closed

Open except when valve is fully opened

Closed only when valve is fully closedClosed except when is fully opened

Opened by torque responsive mechanism, to stop valve opening

Closed by torque reponsive Mechanism to stop valve closing

A circuit breaker, which serves to control or make and break the equalizer

A device functions when the temperature exceeds/ decreases a predetrmined value.

Field winding (Rotor) over temperature

Transformer oil over temperature

Transformer winding over temperature

A device, which functions on a given value of under-voltge.

It is used for designating under/ over voltage protection.

A relay, which functions on a desired value of power flow in a given direction.

A relay, which functions when the circuit addmittance, impedance, or reactance increasesor decreases beyound pre-determined value.

A device functons to raise or to lower the temperature of a machine or other apparatuswhen its temperature varies beyound a predetermined value.

(This device number is widely used for designating Volt/Hertz protection of generator).

A device operates when two AC circuits are within the desired limits of frequncy, phaseangle, or voltage to permit the paralleling of these two AC circuit

It is used for designating inadvertent energization protection of altenator

An isolator used expressly for disconnecing one circuit from another for the prupose ofemergency operation.

A non-automatically reset relay which gives a number of separate visual indications uponthe functioning of protective device.

A device connects a circuit such as the shunt field of a synchroous converter to a source ofseparate excitation during starting sequence.

A device used for makes and break contacts when the main device or apparatus, which hasno device function number, reaches a given position.

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Motor bearing, inboard

Motor bearing, outboard

Pump bearing, inboard

Pump bearing, outboard

Compressor bearing, inboard

Compressor bearing, outboard

Gear bearing, low speed,inboard

Gear bearing, low speed, outboard

Gear bearing, high speed,inboard

Gear bearing, high speed, outboard

Viberation Monitor

Seal Failure Monitor

A device, which functions to apply or remove the field excitation of a machine.

Explosive atmosphere monitor

Smoke monitor

A multi-contact switch, which fixes the operating sequences of major devices during startingand stopping or during other sequential switching operations.

A device used for raising, lowering or shifting the brushes of a machine, or for short-circuiting of slip rings.

A device operates or permits the operation of another device on a predetermined polarity

only.A device, which functions when the current or power flow decreases below a predeterminedvalue.

A device, which functions on excessive bearing temperature or on other abnormalmechanical conditions such as undue wear, which may eventually result in excessivebearing temperature.

A device, which functions upon the occurrence of an abnormal mechanical condition suchas vibration and seal failure.

A relay, which functions on failure of machine field current or on excessive value of thereactive component of armature current in AC machine.

A device whose principal function is to connect a machine to its source of running voltageafter having been brought up to the desired speed on the starting connection.

A device transfer the control circuits so as to modify the plan of operation of the switchingequipment or of some of the devices.

a device, which functions to start the next available unit in amultiple,unt equipment on thefailure or on the non-availablity of the preceding unit.

A device, which function upon the occurrence of a predetermined atmospheric conditionsuch as hazardous, explosive atmosphere, smoke or fire.

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Locked rotor current

Instantaneous over current breaker failure protection

Instantaneous over current ground fault relayconnected to neutral

Instantaneous over current earth fault relay

Voltage restraint, instantaneous and time over current relay

Time delayed ground fault over current relay(Standby earth fault relay) connected to neutral

Excessive starting time

Time delayed earth fault over current relay.

Auxiliary switch closed when the circuit breaker is closedAuxiliary switch closed when the circuit breaker is opened

Circuit breaker spring charging limit switch

A relay, which functons when the poly- phase current are of reverse phase sequence orcontains negative phase sequence due to unbalanced load.

A device, which functions upon a predetermined value of poly-phase voltage in the desiredphase sequence.

A device, which returns the equipment to the normal or off position and locks it out if the

normal starting or stopping sequence is not properly completed within a predeterminedtime.

A device, which functions when the temperature of AC machine armature or other loadcarrying winding exceeds a predetermined value.

A relay, which functions instantaneously on an excessive value of current or an excessiverate of current rise.

A relay with either a definite or inverse time characterstics, which functions, when current inan AC circuit exceeds a preset value.

A circuit breaker, which is used to close and interrupt an AC power circuit under normalconditions or to interrupt this circuit under fault or emergency condition.

Auxiliary switch closed when the operating mechanism of the circuit breaker is in operatedposition

Auxiliary switch closed when the operating mechanism of the circuit breaker is in non-operated position

Latch checking switch, closed when the circuit breaker mechanism linkage is latched afteran opening operation

A device, which forces the DC machine field excitation to build up during starting or whichfunctions when the machine voltage has build up to given value.

A relay, which operates when the power factor in an AC circuit becomes above or below aset value. Also used for automatic switching control of capacitor bank.

A relay, which automatically controls the application of the field excitation to a synchronousmotor at some predetermined point in the slip cycle.

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A device, which functions if one or more of the power rectifier anodes fails to fire.

A relay, which operates on agiven value of over voltage.

Neutral displacement relay (over voltage)100% stator ground fault protection

Voltage transformer fuse failure relay

Transformer main tank Buchholz relay

Transformer tap changer protection relay

Restricted earth fault relay

Differential earth fault protection

Rotor earth fault protection

A equipment which controls the gate or valve opening of prime mover.

Directional phase fault relay

Ground directional relay

A power or stored energy operated device, which functions to short circuit or to ground acircuit in response to automatic or manual means.

A voltage balance relay, which operate on a given difference in voltage between twocircuits. Current balance relay operates on given difference in current input or out in acircuit.

A time delay device, which serves in conjunction with the device, which initiates theshutdown stopping or opening operation in an automatic sequence.

A device, which operates on given values of liquid or gas pressure or on a given rate ofchange of these values.

A device, which functions on the failure of the insulation of a machine, transformer or otherapparatus to ground.

A device, which functions to allow only a specified number of operations of given device orequipment. It also function to energize a circuit or to permit intermittent acceleration orjogging of a machine at lower speeds for mechanical positioning.

A device, which functions on desired value of AC over current flowing in a predetermineddirection.

A device which initiates a pilot singnal for blocking or tripping on external faults in atransmission line or operate with other devices to block reclosing on an out-of-step condition

or on power swings. This device number is also used for desingnating out-of-stepprotection.

A two position manaually operated switch, which in one position permits the closing of acircuit breaker or placing of equipment in operation and in the other position prevents thecircuit breaker or the equipment from being operated.

A rheostat, which is used to vary the resistance of a circuit in response to some means ofelectrical control.

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A switch, which operates on given value or on a given rate of change of level.

Switch reponse level in scrubber

Switch reponse to level in seal oil tank

Switch reponse to level in storage tank

Low oil level

High oil level

A relay, which functions when the current in a DC circuit exceeds a given value.

A relay, which controls the automatic reclosing and locking out of an AC circuit breaker.

A switch operates on a given values or on given rate of change of flow.Switch responsive to flow of room ventilation air

Switch responsive to flow of air to force ventilated motor

Switch responsive to flow of lubricating oil

Switch responsive to flow of seal oil

Switch responsive to flow of water

A circuit breaker used to close close and interrupt a DC power circuit under normalconditions or to interrupt this circuit under fault or emergency conditions.

A contactor used to shunt or insert a step of load limiting, shifting or indicating resistance inpower circuit.

A relay other than annunicator, which is covered under device No. 30, which used tooperate or to operate in connection with visual or audible alarm.

A mechanism, which is used for moving a removable circuit breaker unit to and from theconnected, disconnected and test position.

This unit is used to generate and transmit pluses over a telemetering or pilot wire circuit tothe remote indicating or receiving device.

A relay, which functions at a predetermined phase angle between two voltages or twocurrents or between voltage and current.

A relay, which functions on a predetermined value of frequency either under or over onnormal system frequency or rate of change of frequency

A device, which control the automatic closing and reclosing of a DC circuit breaker generallyin response to load circuit conditions.

A device, which operate to select automatically between certain sources of conditions in anequipment or performs a transfer operation automatically.

Complete electrical mechanism or servomechanism, including the operating motor,solenoids, position switches etc, for a tap chager, induction regulatoror any piece ofapparatus, which has no device function numbers.

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Carrier or pilot wire relay phase comparision via power line carrier communication

Tele protection equipment via OPGW fiber optic cable

Electrically reset locking out relay

Bus differential protection

Bus failure differential protection

Phase segregated curent differential protection for transmission feeder

Generator differential protection

Differential protection for split phase winding generators (turn to turn short circuit)

Motor differential protection

100% Restricted earth fault differential protection

Transformer differential protection

Teed feeder differential protection

Combined generator and transformer differential protection

Spring charge motor of circuit breakerCompressor

Compressor, instrument air

fan

Ventilation fan (delivering air to room)

Exhaust Fan

Fan as space cooling unit

Fan on space heating unit

Fan serving forced ventilated air

Fan serving forced air cooler

LubricatorPump

Pump, lube oil

Pump, seal oil

Sump pump

Water pump

A device used as a disconnecting or isolating switch in AC or DC circuit.

A device, which is operated or restrained by a singal used in connection with carrier-currentor DC pilot wire fault directional relaying.

An electrically operated, hand or electrically reset relay, which functions to shutdown andhold an equipment out of service on the occurance of abnormal condition.

A protective relay, which functions on a precentage of phase angle or other quantitativedifference of two currents or some other electrical quantities.

One equipment used for operating auxiliary equipments such as pumps, blowers, exciter,rotating magnetic amplifiers etc.

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stallations.

A device whose function is to regulate a quantity or quantities such as voltage, current,power, speed, frequency, temperature and load at a certain value.

A relay, which operates when the voltage across an open circuit breaker or contractorexceeds a given value in given direction.

A relay, which permits or causes the connection of two circuits when the voltage differencesbetween them exceeds a given value in a predetermined direction and causes these twocircuits to be disconnected from each other when power flowing, between them exceeds agiven value in opposite direction.

A device functions to increase or decrease in one-step the values of field excitation in amachine.

A device, which function to trip a circuit breaker, contactor or equipment or to permitimmediate tripping by other device or to prevent immediate reclosure of a circuit interrupterin case it should open automatically even through its closing circuit is maintained in closedcondiion.

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Remarks

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Distance relay is being used for phase and ground fault ofthe trasmmision lines.

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Typically DC circuit breaker

Used to designate Loss of field relay / Exciter failure relay

/ reactive power relay

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Negative phase sequence relaly.

Genrator or motor stator winding temprature protection

Frame leakage relay.

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87G Differential Protection Relay

87TD Transverse differential relay

50/51 V Voltage restrained over current relay

26F Rotor winding temperature protection

50/51 G

59N

Neutral displacement relay (over voltage)

46

32 Directional power relay (reverse power relay)

40 Field Failure Relay

64F Field ground relay / Rotor earth fault relay

81 Frequency relay

27/59 Under / over voltage relay

49 Winding temperature protection

95 Back up impedance relay

78 Out of step protection relay

38 Bearing protective Device

12 Over - speed Device

Negative phase sequence relay or phase balancecurrent relay

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25 Synchronizing or synchronism check Device

87TG Baised differential relay

24 Volts / hertz relay (Over fluxing relay)

14 Under Speed Device

25 Synchronism check relay

49 Generator stator winding temperature

32 Reverse power relay

50 / 51 V Voltage restraint over current relay

51 N Standby earth fault relay


64G Restricted earth fault relay

67 Directional over current relay

81 High / low frequency relay

87 G High speed percentage differential relay

12 Over speed switch

14 Low oil pressure switch

15 High engine temperature switch

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Differential protection for split phase winding generators (turn to turn short circuit)

Field winding (Rotor) over temperature

Neutral ground fault relay

Neutral displacement relay (over voltage)

A relay, which functions on a desired value of power flow in a given direction.

It is used for designating under/ over voltage protection.

Generator back up protection impedance relay.

A speed switch which functions on over speed

A relay, which functons when the poly- phase current are of reverse phase sequence orcontains negative phase sequence due to unbalanced load.

A relay, which functions on failure of machine field current or on excessive value of thereactive component of armature current in AC machine.

A relay, which functions on a predetermined value of frequency either under or over onnormal system frequency or rate of change of frequency

A device, which functions when the temperature of AC machine armature or other loadcarrying winding exceeds a predetermined value.

A relay, which functions at a predetermined phase angle between two voltages or two

currents or between voltage and current.

A device, which functions on excessive bearing temperature or on other abnormalmechanical conditions such as undue wear, which may eventually result in excessivebearing temperature.

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Combined generator and transformer differential protection

PROTECTION RELAYS FOR DIESEL ENGINE DRIVEN GENERATORS

A device operates when two AC circuits are within the desired limits of frequncy, phaseangle, or voltage to permit the paralleling of these two AC circuit

A speed switch which functions when the speed of the machine falls below a predeterminedvalue.

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Relay Application

For generator internal protection

Inter turn fault protection i.e. turn to turn fault

Over current and short circuit protection

Protection against rotor winding overheating

Earth fault protection. Relay connected to the neutral CT.

Relay connected to the secondary of earthing transformer

Protection against unbalanced load

Protection against motoring (prime mover / drive failure)

Protection against loss of Excitation

Protection against rotor earth fault

Protection against low or high frequncy.

Protection against low or high voltage

For back up protection of GT unit

Pole slip protection

Protection against bearing over heating

Protection against over speed

Genrator or motor stator winding over temprature /heating protection

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For auto synchronizing generators

To detect voltage regulator malfunction

To dtetect governor failure

Protection against overheating stator winding

Protection against motoring

Overload and short circuit protection

Earth fault protection

Over voltage protection

Earth fault protection of stator winding

Directional protection of paralleled generator

High / low fequency protection

Protection against internal phase faults and earth faults.

For over all protection of combined generator transformerunit

Check difference in bus and generator voltage / phaseangle / frequencies

Shunts down the engine if the engine speed exceeds the

set value or 110%shunts down the engine if the lube oil pressure reducesbelow the set value

Shuts down the engine if the engine temperature exceedsthe set value

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Technical Requirement

Protection against generator winding fault

Only for generators with spli-phase winding.

Applicable only for separately excited generator

Inverse time delay relay for NGR earthing

Mho or reactance relay

DC shunt excitation or thyristor excitation system

Measuring single phase voltage

Measuring three phase voltage

Additional protection for GT combined unit.

Measuring Phase angle

For deisel generator sets and hydro generator

Relay operates even if the sustained fault current islower than full load current

Generator neutral earthed via grounding transformer.Used for combined GT unit.

Time lag over current relay with negative sequencefilter

Inverse time relay for DG set. Definite time relay forturbine generator

RTD embeded in the stator winding detectstemperature

For turbo/ hydro generators. Not for dieselgenerators

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Additional protection for GT combined unit.

Protection against under speed.

Compare bus voltage, frequency and phase anglewith enerator

Protection against over excitation, over fluxing of GTunit.

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87CD Phase segregated current differential protection

87TEED High speed biased differential relay

87BFP

51/51 N Non directional over current and earth fault relay

85 P Pilot wire relay

67 AC directional over current relay

67N AC directional ground fault relay

21 Distance Relay

85PLCC

85TP Teleprotection equipment for power network

54 FL Frame leakage relay

79 Auto reclosing relay

87B

87 B Precentage restraint bus differential relay

21 Switched 3 or 4 zone distance relay

F/D Fault Locator / Disturbance recorder

Power line carrier relaying scheme. (carriercurrent protection)

High impedance circulating current bus differentialrelay

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Phase segregated curent differential protection for transmission feeder

Teed feeder differential protection

Bus failure differential protection


Carrier or pilot wire relay phase comparision via power line carrier communication

Tele protection equipment via OPGW fiber optic cable

A relay, which controls the automatic reclosing and locking out of an AC circuit breaker.

Bus differential protection


A device, which is operated or restrained by a singal used in connection with carrier-currentor DC pilot wire fault directional relaying.

A device, which functions on desired value of AC over current flowing in a predetermineddirection.

A relay, which functions when the circuit addmittance, impedance, or reactance increasesor decreases beyound pre-determined value.

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Relay Application

Phase fault and earth fault protection

Breaker failure protection

Back up over current and earth fault protection

Phase fault protection for Teed feeder lines

Phase fault protection


Inter tripping circuit breaker on the other end of the line

Inter tripping circuit breaker on the other end of the line


Auto reclosing crcuit breaker after a fault trip

Phase fault and earth fault protection in the bus zone

Instantaneous over current relay

Phase fault and earth fault protection

Measuring location of transient / persistent faults

Phase fault and earth fault protection of Teed feeder Busbar

Distance relay is being used for phase and ground fault ofthe trasmmision lines.

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IDMT characteristic, plain over current relay

For double circuit feeders

For double circuit feeders

3 Zone transmission lines

Via OPGW fiber optic cable

For Gas Insulated stations

High impedance circulating impedance relay

Low impedance voltage relay

Applicable only for under grond cable transmission

Record graphically the fault voltage and current

Phase segregated relay for 1 pole and 3 poleoperation

Protection for one-and-half circuit breaker bus bararrangement

Tripping the circuit breakera associated with faultyzone

Suitable for 3 ended short distance lines or cablefeeders

Phase comparision via power line carriercommunication

With provision for dead end closing/ synchronismcheck

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50

50G Instantaneous Earth fault relay

50N Instantaneous phase over current relay fault relay

51

51G Standby earth fault relay

51N IDMT phase over current earth fault relay.

50BF Breaker failure protection relay.


64G Restricted earth fault relay

67N / 87 N

87T High speed based transformer differential relay

64N High Impedance relay.

74 Alarm relay or trip circuit supervision relay

26 W Winding Over temperature

26O Oil Over temperature

63MT Main tank Buchholz relay

63TC Tap changer protection relay (Buchholz type)

Instantaneous over current or rate of rise relay(High set phase over current relay)

AC time over current relay / IDMT phase overcurrent relay

Directional / Differential connection for earth faultprotection

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20

25 Synchronism check relay

27 Under Voltage relay

49 Over current protection

50 Instantaneous over current relay

51 Time delay over current relay

51 N IDMT Earth fault relay

63 B Buchholz relay

26 WT Winding temperature high

Electrical operated valve (Tank over pressurerelief valve)

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Instantaneous over current ground fault relay connected to neutral

Instantaneous over current earth fault relay

Time delayed ground fault over current relay(Standby earth fault relay) connected to neutral

Time delayed earth fault over current relay.

Instantaneous over current breaker failure protection

A relay, which operates on agiven value of over voltage.

Restricted earth fault relay


Transformer differential protection ( High speed based transformer differential relay)

Differential earth fault protection

Transformer winding over temperature

Transformer oil over temperature

Transformer main tank Buchholz relay

Transformer tap changer protection relay

A relay, which functions instantaneously on an excessive value of current or an excessiverate of current rise.


A relay other than annunicator, which is covered under device No. 30, which used tooperate or to operate in connection with visual or audible alarm.

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DISTRIBUSTION SUBSTATATION AND TRANSFORMER PROTECTION

A solenoid or motor operated valve, which is used in vacuum, air gas, oil, water or similarlines. Following suffix letters are used to designate applications:

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Relay Application

Short Circuit Protection

Zero sequence current protection


Over load protection

For back up protection of neutral grounding resistor.


Breaker failure protection

Over voltage /over fluxing protection

Internal - earth fault protection

Differential ground fault protection

Protection circuit Supervpsion

Winding over heating protection

Cooling system control

Short Circuit / Winding damages.

Flash over /Fault in tap changer

Directional / Differential connection for earth faultprotection

Internal protection (short circuit, earth fault, fault in tapchanger).

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Incipient faults.

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Relay operates due to short circuit fault.

Inverse Definite Minimum Time (IDMT) characteristic

Earth fault protection.

Dial type winding thermometer

dial type oil thermometer

Operates due to oil surge or gas.

Oil surge in the tap changer tank.

Relay is connected to the CT provided in the neutralbushing / neutral earthing

Relay operates due to Earth fault in primary,secondary and tap changer.

For two winding transformer relay is required in theprimary only, but for three winding transformer relayis required in all the three windings.

Relay is connected to the CT installed before neutral

grounging resistor.

If the primary protection fails to trip the CB relay willinitiate a trip of all of the CB associated with thesame bus section.

Relay operate due to over voltage or due tosuturation of magnetic circuit.

For deita connected or un earthed star winding, relayis connected to residual circuit of the CT.

Star connected winding, CT"s are connected in deltaand delta connected winding CT's are connected instar.

For transformers grounded through groundingresistor.

Relay operates if CT circuit wiring becomes opencircited.

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Excessive oil pressure in the main tank.

device no

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