17648889 introduction to power system protection relays
TRANSCRIPT
P. GOPALA KRISHNAADE/400KV/APTRANSCO
Power Systems Protection -Introduction
Power Systems Protection -Introduction
Power Evacuation Substation
Transmission Substation
Switching Substation
Distribution Substation
Power System Components
1. Generators2. Transformers3. Transmission Lines4. Feeders5. Motors6. Capacitor Banks7. Bus Bars8. Reactors
Power Systems Protection -Introduction
Power Systems Protection -Introduction
Why we need the Protection ?To detect abnormalities (faults).
To eliminate such abnormality by
isolating smallest portion of the system
in a shortest period of time.
To prevent injury to personnel.
To prevent damage to Equipment.
Enable Continuous service in
undamaged part of the network.
Power Systems Protection -Introduction
Protective Relay – What should it do ?Monitor system parameters continuously
(V, I, P, F)
Operate quickly when necessary
(Dependability)
Should not operate wrongly
(stability, discrimination)
To trip or not to trip ?
Power Systems Protection -Introduction
Protective System – What are the Requirements?SpeedThe relay must operate at the required speed. It should neither be too slow which may result in damage to the equipment nor should it be too fast which may result in undesired operation. Damage can be Minimised.
SensitivityThe relaying equipment must be sufficiently sensitive so that it operates reliably when required under the actual conditions that produces least operating tendency and to detect all possible Shunt and series Faults.
SelectivityThe relay must be able to discriminate (select) between those conditions for which prompt operation is required and those for which no operation, or time delayed operation is required. Isolate only Faulty Section without disturbing Healthy Section.
ReliabilityThe most important requisite of protective relay is reliability since they supervise the circuit for a long time before a fault occurs; if a fault then occurs, the relays must respond instantly and correctly. The Operation Capability of the Protection System is summerised in “ reliability”, which includes both the security in fault clearance and the security against undesired clearances. The security in fault clearance is called dependability and the security against undesired clearances is called Security.
Power Systems Protection -Introduction
Protective Relay Scheme – What is it ?
A Protective RelayCT / CVT / PT(EMVT)Auxiliary Power Supply (24 V to 240 V AC/ DC)Switching Device ( Breaker/ Isolator / Contactor)Trip CoilAlarm / Trip contactControl Wiring
Power Systems Protection -Introduction
Power System - Faults
CurrentOver LoadOver CurrentEarth FaultCurrent UnbalanceDir. Over CurrentDir. Earth Fault
VoltageOver VoltageUnder VoltageVoltage UnbalanceNeutral shift
FrequencyOver FrequencyUnder FrequencydF/dT
PowerActive powerReactive powerOver powerUnder powerReverse power
ComputedOver fluxingLoss of fieldDifferential Over CurrentRestricted E/FUnder Impedance
Control/ManagementSynchronisingLoad sharingIslandingLoad shedding
DC Relays
Power Systems Protection -Introduction
Protection – ANSI Codes
Code numbersUsed to denoteProtectionsOn a SLD
Power Systems Protection -Introduction
Power System – Fault Handling
Trip & Isolate
Breaker is tripped on fault
Faulty section is isolated
Control & RegulateBreaker is not trippedCorrective actions Generated on line
Power Systems Protection -Introduction
Relay operation when a fault occurs
Each Relay should Protect a specific Zone in the System.
If fault is inside its Zone, Relay should operate and isolate the faulted Zone.
If fault is outside zone, Relay should not operate,
Some other Relay should operate and isolate
Power Systems Protection -Introduction
What happens when a fault occurs
Fault current flows through number of Relays.
Some of these Relays will start to operate.
Only one Relay related to particular fault should trip and interrupt the fault current.
Remaining Relays will reset after above.
Power Systems Protection -Introduction
Protection Relays – Inputs / Out puts
Inputs
Current CTsVoltage PTsFrequency PTsPower CTs + PTs
Outputs
Trip Contact
Power Systems Protection -Introduction
Protection Relays – Settings
Pick up setting Low setHighset
Time delay setting Definite timeInverse time
% of CTRating
TMSSetting
Power Systems Protection -Introduction
Power System – Trip time characteristics
I/Is
t
10
1.3 or3.0 sec
I/Is1.4LS
Power System – Trip time characteristics
I/Is
t
10
1.3 or3.0 sec
50 msec
6HS
1.4LS
Power Systems Protection -Introduction
Typical Inverse Time Delays
Power Systems Protection -Introduction
0.710.961.501.932.704.5013.50Very Inverse 1.5 sec
2.292.543.003.333.875.0310.13Normal Inv 3 sec
0.991.101.301.441.682.1804.39Normal Inv 1.3 sec
TIME MULTIPLIER SETTING – TMS : 1.00
0.200.360.811.272.285.3326.66Extremely Inverse
I/Is=20I/Is=15I/Is=10I/Is=8I/Is=6I/Is=4I/Is=2
ApplicationSLD representationFront panel ControlsBack Panel terminationsInputs / Outputs / RatingsSettings (Inside)Settings (on front panel)Installation & wiringCommissioningTesting (Front panel)Testing (SCITS)Cat . No.
Things you should know
Power Systems Protection -Introduction
EVALUATION OF
PROTECTIVE RELAYS
PREPARED BYGOPALA KRISHNA PALEPU
ADE/MRT(PROTECTION)
1 ST GENERATIONFIRST GENERATION RELAYS :
THESE ARE ELECTRO MAGNETIC RELAYS
IN THIS NO OF ELECTROMAGNETIC RELAYS PROVIDED FOR ARRIVING
A SPECIFIC FUNCTION i.e EACH FUNCTION OF THE SCHEME HAVING A
SEPARATE RELAY. COMBINING ALL IS CALLED ONE PROTECTION
FUNCTION. NO OF RELAYS ARE MORE AND SPACE OCUPATION IS
MORE AND INTER CONNECTION WIRING DIAGRAM IS MORE.
DISADVANTAGES: ELECTROMECHANICAL RELAYS HAVE A LOT OF
MECHANICAL PARTS, WHICH MAY BECOME CLOGGED WITH DIRT OR
CORRODED DUE TO ENVIRONMENTAL CONDITIONS, AFFECTING BOTH
OPERATION, CALIBRATION AND MOVEMENT OF THE DISKS. IT
REQUIRES PERIODICAL MAINTANENCE AND ADJUSTMENT.
1 ST GENERATIONNEXT MODIFICATION :
ELECTRO MAGNETIC RELAYS WITH STATIC COMPONENTS
IN THIS SOME OF THE FUNCTIONS ARE DERIVED FROM STATIC
COMPONENTS PROVIDED ON THE PCB. IN THIS QUANTITY OF
ELECTROMAGNETIC RELAYS ARE REDUCED. COMBINING ALL IS
CALLED ONE PROTECTION FUNCTION. QUANTITY OF RELAYS ARE
REDUCED AND SPACE OCUPATION IS REDUCED SOME WHAT.
DISADVANTAGES: THE PCBs ARE MADE WITH TRANSISTORS AND ARE
BROUGHTOUT ITEMS WITH DIFFERENT MAKE. AFTER SOME TIME
THESE ARE TO BE REPLACED FOR CORRECT OPERATION WITHOUT
DRIFT. THE PCBs & COMPONENTS PERFORMANCE MAY BE AFFECTED
DUE TO DIST & DIRT. IT REQUIRES PERIODICAL MAINTANENCE AND
ADJUSTMENT.
2 ND GENERATIONSECOND GENERATION RELAYS :STATIC RELAYS WITH TRANSISTORSIn this all of the functions are derived from static components provided on the PCB. In this initially each function is derived with separate static relay. Quantity of static relays are more but space occupation is less. Combining all is called one protection function. Inter connection wiring diagram is still not reduced. DISADVANTAGES: Static relays generally employ a lot of electronic components made by other manufacturers. If these electronic components are not tested with rigorous quality control, the chances of failure of components during the relay life time may exist. A reliable DC power source within the relay, to electronically measure circuits has to be generated from available external power sources. Most of the static relays employ series, shunt, or switched mode power supply designs. For a variety of reasons, if these power supplies fail, the measuring circuits are inoperative and the relay is dead for any measurements. No protection is available to the network. Most of the static relays in use do not have the means to detect the failure of power supply and initiate an alarm. It requires periodical Maintenance.
2 ND GENERATIONNEXT MODIFICATION :
STATIC RELAYS ON SINGLE PCBIN THIS ALL OF THE FUNCTIONS ARE DERIVED FROM STATIC COMPONENTS PROVIDED ON THE PCB. IN THIS ALL STATIC RELAYS ARE TAKEN TO ONE MASTER PCB AND EACH FUNCTION PCB WILL BE ADD ON CARD TYPE. SO TOTAL RELAY IS ONE BUT FOR EVERY FUNCTION IS PCB IS AVAILABLE AND CONNECTED TO MAIN PCB. SPACE OCCUPATION IS LESS. COMBINING ALL IS CALLED ONE PROTECTION FUNCTION. NO INTER CONECTION WIRING. THIS IS PART OF MAIN PCB. DISADVANTAGES:DISADVANTAGES ARE SAME AS ABOVE.
3 ND GENERATIONTHIRD GENERATION RELAYS :
STATIC RELAYS WITH ICsIN THIS NO OF COMPONENTS ARE REDUCED AND BROUGHT OR BUILT IN ONE INTEGRATED CHIP. DUE TO THIS THE RELAY SIZE IS REDUCED AND SOME OF THE FUNCTIONS ALSO TAKEN IN TO ONE INTEGRATED CHIP. THIS ALSO BUILT IN ONE PCB. ALL OF THE FUNCTIONS ARE DERIVED FROM STATIC COMPONENTS PROVIDED ON THE PCB. IN THIS ONLY MASTER PCB IS AVAILABLE, NO SEPARATE PCB FOR EACH FUNCTION , ALL ARE INTEGRATED IN ONE PCB. PROBLEMS ARE SOME WHAT REDUCED. SPACE OCCUPATION IS LESS. ONE PROTECTION FUNCTION ONLY ONE RELAY AND ALL FUNCTIONS ARE INTEGRATED. NO INTER CONNECTION WIRING DIAGRAM.
3 ND GENERATION
NEXT MODIFICATION :
SEMI NUMERIC RELAYSIN THIS SOME FUNCTIONS ARE CAN BE PROGRAMMABLE AND INTERFACE THROUGH PC. SOME ICs ARE HAVING THE FACILITY TO INTERACT THROUGH COMMUNICATION PORT. IT IS SOME WHAT MODIFICATION TO IC BASED RELAYS. IN THIS SOME FUNCTION CAN BE ENABLED AND DISABLED, BASED ON THE REQUIREMENT.
4 ND GENERATION
MICROPROCESSOR BASED NUMERICAL RELAYSIN THIS ALL OF THE FUNCTIONS ARE BROUGHT ON ONE IC. THE FOURTH GENERATION PROCESSOR-BASED RELAYS, DO HAVE THE WATCHDOG FEATURE, WHICH FACILITATES THE CHECKING OF POWER SUPPLY FAILS, CLOCK FREQUENCIES, AND OTHER PATTERNS. MOST OF THESE RELAYS HAVE AUTO TEST FEATURES WHICH TEST THE ELECTRONIC CIRCUIT FUNCTIONS AT REGULAR INTERVALS & AUTOMATICALLY.
MICROPROCESSOR BASED RELAYS
BACK GROUND WORK
ADVANTAGES & DISADVANTAGES
OPERATIONS & ALGORITHMS IN MICROPROCESSOR
FUNCTIONAL BLOCKS & OTHER HARDWARE OF MICROPROCESSOR BASED RELAY
FILTERING TECHNIQUES
TESTING OF MICROPROCESSOR RELAYS
MICROPROCESSOR BASED RELAYS - BACKGROUND WORK
1960sA FEW CONCEPTS WERE PROPOSED
HARDWARE WAS VERY EXPENSIVE
BENEFITS OF MICROPROCESSORS FOR RELAYS WERE NOT CLEAR
IEEE ARTICLE “FAULT PROTECTION WITH A DIGITAL COMPUTER” OUTLINED THE FEASIBILITY & PROBLEMS ASSOCIATED IN S/S PROTECTION WHEN A DIGITAL COMPUTER IS USED.
MICROPROCESSOR BASED RELAYS - BACKGROUND WORK
1970sTWO PAPERS WERE PUBLISHED“DIGITAL CALCULATION OF IMPEDANCE FOR TRANSMISSION LINE PROTECTION”“ 3 PH TRANSMISSION LINE PROTECTION WITH A DIGITAL COMPUTER”
PROMINENT MANUFACTURERS LIKE WESTINGHOUSE, IBM STARTED INVESTIGATING S/S COMPUTER SYSTEMS
PHILADELPHIA ELECTRIC & GE INITIATED PROJECTS ON DIGITAL TECHNIQUES FOR PROTECTION
VARIOUS ALGORITHMS WERE DERIVED FOR DIGITAL CALCULATION OF PROTECTION PARAMETRS
EXPERIMENTAL SYSTEMS WERE BUILT BY GE & WESTINGHOUSE TO CHECK ALGORITHMS
FIRST GENERATION OF MICROPROCESSOR BASED RELAYS BUILT
MICROPROCESSOR BASED RELAYS - BACKGROUND WORK
1980sMAJOR MANUFACTURERS LIKE ABB, GE, GEC , TOSHIBA, SIEMENS START DESIGN & SALES OF BROAD RANGE OF PRODUCTS FOR POWER SYSTEM PROTECTION
MICROPROCESSOR IMPROVES PERFORMANCE SPECS FOR OPERATION IN INDUSTRIAL ENVIRONMENT
MANY PLC BASED SYSTEMS ARE COMMISSIONED IN INDIA BY L&T, SIEMENS, ECIL ETC.
MANY ELECTRICITY BOARDS & PROCESS PLANTS IN INDIA START USING MICROPROCESSOR BASED INSTRUMENTS
THE WORD SCADA GETS POPULAR IN INDIA
PGCIL GOES IN FOR MICROPROCESSOR BASED DISTANCE RELAYS IN INDIA
MICROPROCESSOR BASED RELAYS - BACKGROUND WORK
1990sABB & GEC ALSTOM INTRODUCED RANGE OF MICROPROCESSOR BASED RELAYS FOR ALL UNIT PROTECTIONS
MAJOR MANUFACTURERS LIKE ABB, GE, GEC , TOSHIBA STARTS DESIGN & SALES OF BROAD RANGE OF PRODUCTS FOR POWER SYSTEM PROTECTION
MANY ELECTRICITY BOARDS & PROCESS PLANTS IN INDIA START USING MICROPROCESSOR BASED INSTRUMENTS
PGCIL GOES IN FOR MICROPROCESSOR BASED DISTANCE RELAYS IN INDIA
MICROCONTROLLERS / DSPs ARE INTRODUCED IN LATE 90s BY HARDWARE MANUFACTURERS WHICH HAVE IMPROVED THE SPEED OF OPERATION.
PARAMETER NUMERIC CONVENTIONAL
ACCURACY 1% 5% / 7.5%BURDEN < 0.5 VA > 5 VASETTING RANGES WIDE LIMITEDMULTI FUNCTIONALITY YES NOSIZE SMALL LARGEFIELD PROGRAMMABILITY YES NOPARAMETER DISPLAY YES NOSYSTEM FLEXILBILITY YES NOCO-ORDINATION TOOLS MANY TWOCOMMUNICATION YES NOREMOTE CONTROL YES NOSPECIAL ALGORITHMS MANY LIMITEDSPECIAL PROTECTIONS YES NOSELF DIAGNOSTICS YES NO
ADVANTAGES OF NUMERIC RELAYS
DIS-ADVANTAGES OF NUMERIC RELAYS
SOFTWARE INTENSIVE
OBSOLESENCE RATE
EMI / EMC PROBLEMS
SERIAL NATURE
PROTECTION ALGORITHM
MEASUREMENMT METHOD
TRIP TIME CALCULATION
GOOD FILTERING CHARACTERISTIC(HARMONICS, NOISE, DC SHIFT)
FAST TRIP DECISION
FUNCTIONAL BLOCKS OF A NUMERIC RELAY
ANALOGINPUT
SU-SYSTEM
DIGITALINPUT
SUB-SYSTEM
POWER SUPPLY
MICROPROCESSOR
COMMUNICATIONINTERFACE
RAM
ROMEPROMFLASH
DIGITALOUTPUT
SUB-SYSTEM
DSP
ANALOG INPUT SUB SYSTEM
CT
PT
SURGESUPPRESSION
SURGESUPPRESSION
ANALOGFILTER
ANALOGFILTER
MUX A / DCONVERTER
MICROPROCESSOR
MICROPROCESSORS Vs MICRO CONTROLERS
CONTROL
CONTROL
Accumulator
Arithmetic LogicUnit
Data Register
Address Register
Data Register
Arithmetic Logic Unit
Address Register
Accumulator
I/OROMRAM
EPROM
TimersCounters
UART
Microprocessor Micro controller
RELAY HARDWARE
NORMALLY 400KV RELAYS SUPPLIED WITH FOLLOWING CONFIGUARATION/HARDWARE
1. MIN 4Nos MAX 8Nos COMMAND/TRIP OUTPUTS 2. MIN 24Nos SIGNAL OUTPUTS3. MIN 14 LED INDICATIONS4. MIN 24 BINARY INPUTS
PCMODEM
IRIG-BRE/CC
16 / 32 BIT
SELF DIAGNOSTICS - TECHNIQUES USED
RAM Checked by computing a checksum of memory contents and comparing it against a stored factory value.
RAM Checked by periodically writing a specific data and reading back the memory contents
A / D Checked by inputing a known value of + / - voltage.Any off set at a given time, is software corrected.
SETTINGS Checked by checksums or CRC values can be stored and compared. Often, 2 or 3 copies of settings are stored and compared.
POWER Checked by monitoring power supply voltage values SUPPLY from A / D converter.
TYPES OF SIGNALS REQUIRED FOR PROPER PROTECTION
Current, Voltage and Distance Relays :Require fundamental frequency component signals. All other signals will interfere with protection process.
Harmonic Restraint Relays :Require both the fundamental & the Harmonic components , each value separately, for decision making process.
4 ND GENERATION1ST DEVELOPMENT:SOFTWARE DEVELOPMENT IS APPLICATION BASED RELAYS i.e EACH PROTECTION FUNCTION HAVING SEPARATE SOFTWARE & HARDWARE.
Example:1. LINE PROTECTION,2. TRANSFORMER PROTECTION,3. BUSBAR PROTECTION, 4. GENERATOR PROTECTION5. MOTOR PROTECTION6. REACTOR PROTECTION7. CAPACITOR PROTECTION
4 ND GENERATION2ND DEVELOPMENT:SOFTWARE DEVELOPMENT IS SOME GROUP BASED RELAYS i.e SOME PROTECTION FUNCTIONS ARE TAKEN IN TO ONE FLATFORM AND PROVIDED COMMON SOFTWARE.FROM THIS INBUILT FACILITY OF EVENT RECORDER AND DISTURBANCE RECORDER IS DEVELOPED.
Example:ABB: 1. REX 5xx SERIES FLATFORM
2. REX 316 SERIES FLATFORM3. REX 670 SERIES FLATFORM4. RED 500 SERIES FLATFORM5. RED 600 SERIES FLATFORM
4 ND GENERATION3RD DEVELOPMENT:UNIVERSAL SOFTWARE FOR ALL TYPES OF RELAYS FOR PARTICULAR MANUFACTURER. i.e. ONE SOFTWARE ONE MANUFACTURER.
Example:1. SIEMENS: SIPROTEC SERIES – DIGSI2. GE MULTILIN: ENERVISTA3. AREVA : MICOM S1
4 ND GENERATION4TH DEVELOPMENT:UNIVERSAL HARDWARE FOR ALL TYPES OF RELAYS FOR PARTICULAR MANUFACTURER. ONE HARDWARE FOR ONE MANUFACTURER. BUT IT IS MODULAR DESIGN. RELAY IS COMMON HARDWARE BASED ON PROTECTION FUNCTION, PARTICULAR CARD IS ADDED.
Example:1. GE MULTILIN: UR SERIES & SR SERIES
4 ND GENERATION5TH DEVELOPMENT:EACH MANUFACTURER ADOPTING THEIR PROPERITIERY BASED PROTOCOL FOR COMMUNICATION, INTERFACING, NETWORKING AND AUTOMATION. SOME UTILTIES ARE REQUESTED MANUFACTURERS TO SUIT THEIR ADOPTED PROTOCOL. Example:1. UCA – Utility communication architecture2. LON3. SPA4. PROFIBUS5. MODBUS6. DNP7. FIELDBUS8. MVB9. IEC 60870
4 ND GENERATION6TH DEVELOPMENT:BASED ON THE EXPERIENCE WITH DIFFERENT PROTOCOLS, NEED FOR UNIFORMITY AND KNOW –HOW FOR GLOBAL CONSIDERATIONONE WORLDONE TECHNOLOGYONE STANDARDA UNIVERSAL PROTOCOL FOR COMMUNICATION, INTERFACING AND NETWORKING IS DEVELOPED. ALL MANUFACTURERS ARE FORM A GROUP AND PROTOCOLS ARE STANDARDIZED. ANY RELAY CAN BE COMMUNICATED FOR COMMON COMMUNICATION PROTOCOL, i.e INTEROPERATABULITY. THIS IS SPECIAL FOR AUTOMATION OF STATIONS.Example:1. IEC 61850
BENIFITS OF UNIVERSAL PROTOCOL
Innovation & Expansionfirm rules for the description of new
data- objects and functionsInteroperability is maintained
Efficient maintenancerobust data modellingself-descriptive equipment automation-configuration in XML
Separation from Application & Communication
data and application stay secure independent from communication
systemsunconstrained further development of
the technology
Quicker project executioncomprehensive data modelclear, standardised project-
and equipment descriptionConfiguration of substation in XML
ETHERNET & TCP/IPAdopted worldwide Scalable technologyCommon use of infrastructure
One Protocol
for all the needs in the substationflexible configuration
no gateways required
INTEROPERATABULITY WITH ABB, AREVA & SIEMENS
TECHNOLOGY COMPARISION
Freely ConfigurableFixedFixedContacts &Assignments
Analogue to Digital Conversion, Numerical Algorithms, Techniques, Evaluation Trip Criteria
Level Detectors Comparison with Reference Value in Analogue Comparators
Electrical Quantities converted into Mechanical Force & Torque
Measuring Method
CountersStatic TimersMechanical Clock works, Dashpot
Timing Function
Microprocessors, Digital ICs, Digital Signal Processors
Discrete R L C, Transistors, Analogue ICs, Comparators
Induction Discs, Electromagnets, Induction cups etc
Measuring Elements & Hardware
Trip Relays are Inbuilt
Additional Trip Relay Required
Additional Trip Relay Required
Trip Command
LEDs & LCD Display
LEDsFlags, TargetsVisual Indication
NUMERICALSTATICELECTROMECHANICALSUBJECT
TECHNOLOGY COMPARISION
PossibleNot PossibleNot PossibleMultiple Characteristics
PossibleNot PossibleNot PossibleMultiple Integrated Protection func
Not required as settings are stored permanently in Memory in Digital Format
Required as settings drift due to ageing
Frequently Required as settings drift due to ageing
Calibration
Most CompactModular, CompactBulkyHardware SizeHuman Machine Interface, Softwares
Thumb Wheel, Potentiometers, DIP Switches
Plug Setting, Dial Setting
Parameter Setting
AvailableNot PossibleNot PossibleSequence of Events
AvailablePartially AvailableNot AvailableSelf Supervision
Available & Freely Configurable
Not AvailableNot AvailableBinary Input & Output
NUMERICALSTATICELECTROMECHANICALSUBJECT
TECHNOLOGY COMPARISION
Extension and New development Possible and Open Architecture
FixedFixedSolution
Stored In MemoryNot PossibleNot possibleFault History
Protection Control & Monitoring
Protection & Monitoring
Only ProtectionProtection Control & Monitoring
PossibleNot PossibleNot PossibleService value Indication
InbuiltExternal HardwareExternal HardwareDisturbance Recording
WideModerateLimitedRange of Settings
LowerLower Than Electromechanical & Moderate
HigherBurden on CTs, PTs & CVTs
AvailableNot PossibleNot PossibleCommunication facility
NUMERICALSTATICELECTROMECHANICALSUBJECT
Relay ANSI Numbers (IEEE C37.2)
Carrier or Pilot wire Receive Relay85Inst Over-Current Relay50Operating Mechanism84M/C or T/F Thermal Relay49
Trip circuit supervision Relay95Over-Voltage Relay59Over-Flux Relay99Voltage / Current balance Relay60
Isolator or Disconnector89Exciter or DC Generator Relay53
Voltage Directional Relay91Power Factor Relay55
Voltage or Directional Power Relay92Field Application Relay56
Differential Relay87AC Circuit Breaker52Lockout/Tripping Relay86AC IDMT Over-Current Relay51
Automatic selective control or Transfer Relay83Negative phase sequence Relay46
AC Auto Reclosure Relay79Under Current / Power Relay37Frequency Relay81Field failure (loss of excitation)40
Density Switch or Sensor61Time delay relay2Pressure Switch63Interlocking relay3
Phase Angle measuring or out of step Relay78Directional Power Relay32DC Over-Current Relay76Annunciation relay30
Directional Over Current Relay67Volts per Hertz Relay24Blocking/Locking Relay68Synchronism Check Relay25
Restricted Earth Fault Relay64Distance Relay21
Alarm Relay74Isolating Contactor29DC Circuit Breaker72Under Voltage Relay27
DEVICENUMBERDEVICENUMBER