Comparison of Protection Relay Types

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Comparison of Protection Relay Types
Comparison of Protection Relay Types (photo by

Comparison Table

This comparison summarize characteristics of all protection relay types described in previously published technical articles:

  1. Using Protective Relay For Fighting Against Faults
  2. The Good Old Electromechanical Protective Relay
  3. The Solid State Relay (Static Relay) Overview
  4. Few Words About Digital Protection Relay
  5. Flexibility and Reliability of Numerical Protection Relay
CharacteristicEl. Mech. RelayStatic RelayDigital RelayNumerical Relay
Technology Standard1st generation relays.2nd generation relays.Present generation relays.Present generation relays.
Operating PrincipleThey use principle of electromagnetic principle.In this relays transistors and IC’s been usedThey use microprocessor. Within built software with predefined valuesThey use microprocessor. Within built software with predefined values
Measuring elements/ HardwareInduction disc, electromagnets, induction cup, balance beamR, L, C, transistors, analogue ICs comparatorsMicroprocessors, digital ICs, digital dignal processorsMicroprocessors, digital ICs, digital signal processors
Measuring methodElectrical qtys converted intomechanical force, torqueLevel detects,comparison withreference value in analogue comparatorA/D conversion, numerical algorithm techniquesA/D conversion, numerical algorithm techniques
Surrounding EnvironmentDepend upon gravitation and the value changes to the surrounding magnetic fields also.There value may vary with respect to temperature also.
CharacteristicEl. Mech. RelayStatic RelayDigital RelayNumerical Relay
Relay SizeBulkySmallSmallCompact
Speed of ResponseSlowFastFastVery fast
Timing functionMechanical clock works, dashpotStatic timersCounterCounter
Time of AccuracyTemp. dependantTemp. dependantStableStable
Vibration ProofNoYesYesYes
Requirement of Draw OutRequiredRequiredNot requiredNot required
CT BurdenHighLowLowLow
CT Burden8 to 10 VA1 VA< 0.5 VA< 0.5 VA
CharacteristicEl. Mech. RelayStatic RelayDigital RelayNumerical Relay
Reset TimeVery HighLessLessLess
Auxiliary supplyRequiredRequiredRequiredRequired
Range of settingsLimitedWideWideWide
Isolation VoltageLowHighHighHigh
FunctionSingle functionSingle functionMulti functionSingle function
MaintenanceFrequentFrequentLowVery Low
Resistance100 mille ohms10 Ohms10 Ohms10 Ohms
Output Capacitance< 1 Pico Farad> 20 Pico Farads> 20 Pico Farads> 20 Pico Farads
CharacteristicEl. Mech. RelayStatic RelayDigital RelayNumerical Relay
Deterioration due to OperationYesNoNoNo
Relay ProgrammingNoPartiallyProgrammableProgrammable
SCADA CompatibilityNoNoPossibleYes
Operational value indicationNot PossiblePossiblePossiblePossible
Visual indicationFlags, targetsLEDsLEDs, LCDLEDs, LCD
Self monitoringNoYesYesYes
Parameter settingPlug setting, dial settingThumb wheel, dual in line switchesKeypad for numeric values, through computerKeypad for numeric values, through computer
Fault Disturbance RecordingNot possibleNot possiblePossiblePossible

Relay’s Nomenclature as per ANSI

NoType of Relay
2Time delay relay
33 Checking or Interlocking relay
2121 Distance relay
25Check synchronizing relay
27Under voltage relay
30Annunciation relay
32Directional power (Reverse power) relay
37Low forward power relay
40Field failure (loss of excitation)
46Negative phase sequence relay
49Machine or Transformer Thermal relay
50Instantaneous Over current relay
51A.C. IDMT Over current relay
52Circuit breaker
52aCircuit breaker Auxiliary switch “Normally open” (‘a’ contact)
52bCircuit breaker Auxiliary switch “Normally closed” (‘b’ contact)
55Power Factor relay
56Field Application relay
59Overvoltage relay
64Earth fault relay
67Directional relay
68Locking relay
74Alarm relay
76D.C Over current relay
78Phase angle measuring or out of step relay
79AC Auto reclose relay
80Monitoring loss of DC supply
81Frequency relay
81 UUnder frequency relay
81 OOver frequency relay
83Automatic selective control or transfer relay
85Carrier or pilot wire receive relay
86Tripping Relay
87Differential relay
87GGenerator differential relay
87GT Overall differential relay
87UUAT differential relay
87NTRestricted earth fault relay
95Trip circuit supervision relay
99Over flux relay
186AAuto reclose lockout relay
186BAuto reclose lockout relay

Relays for Transmission and Distribution Lines protection

1400 KV Transmission LineMain-I: Non switched or Numerical Distance Scheme
Main-II: Non switched or Numerical Distance Scheme
2220 KV Transmission LineMain-I : Non switched distance scheme (Fed from Bus PTs)
Main-II: Switched distance scheme (Fed from line CVTs) With a changeover facility from bus PT to line CVT and vice-versa
3132 KV Transmission LineMain Protection: Switched distance scheme (fed from bus PT).
Backup Protection: 3 Nos. directional IDMT O/L Relays and
1 No. Directional IDMT E/L relay.
433 KV LinesNon-directional IDMT 3 Over Current and 1 Earth Fault relays
511KV LineNon-directional IDMT 2 Over Current and 1 Earth Fault relays

– Handbook of Switchgear – Bhel – Digital/Numerical Relays – T.S.M. Rao

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About Author


Jignesh Parmar

jiguparmar - Jignesh Parmar has completed M.Tech (Power System Control) ,B.E(Electrical). He is member of Institution of Engineers (MIE),India. Membership No:M-1473586.He has more than 13 years experience in Transmission -Distribution-Electrical Energy theft detection-Electrical Maintenance-Electrical Projects (Planning-Designing-Technical Review-coordination -Execution). He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. He has published numbers of Technical Articles in "Electrical Mirror", "Electrical India", "Lighting India", "Industrial Electrix"(Australian Power Publications) Magazines. He is Freelancer Programmer of Advance Excel and design useful Excel base Electrical Programs as per IS, NEC, IEC,IEEE codes. He is Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Share his experience & Knowledge and help technical enthusiasts to find suitable solutions and updating themselves on various Engineering Topics.