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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
24 For Future applications
25 Synchronizing or synchronism check Device
26 Apparaus Thermal Device
26F
26O
26 W
27 Under Voltage Relay
27/50
27/59
28 For Future applications
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
61 For Future applications
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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Device No. Relay Title
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
59 Over voltage 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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Definition and Function
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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Device No. Relay Title
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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Definition and Function
Phase segregated curent differential protection for transmission feeder
Teed feeder differential protection
Bus failure differential protection
Ground directional relay
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 relay with either a definite or inverse time characterstics, which functions, when current inan AC circuit exceeds a preset value.
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
Earth fault protection
Inter tripping circuit breaker on the other end of the line
Inter tripping circuit breaker on the other end of the line
Earth fault protection
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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Technical Requirement
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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Device No. Relay Title
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.
59 Over voltage 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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Definition and Function
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
Ground directional 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 with either a definite or inverse time characterstics, which functions, when current inan AC circuit exceeds a preset value.
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
Earth fault protection
Over load protection
For back up protection of neutral grounding resistor.
Earth fault protection
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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Technical Requirement
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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8/7/2019 Device No.
44/44
Excessive oil pressure in the main tank.