This document provides an overview of power system protection and protective relays. It discusses the different types of substations in a power system and components that require protection. The key requirements for a protective system including speed, sensitivity, selectivity and reliability are outlined. The document describes the evolution of protective relays from electromagnetic relays to modern microprocessor-based numerical relays. The various generations of relays including their advantages and disadvantages are summarized. Protective relay schemes and their inputs, outputs, settings and applications are also discussed briefly.

1. P. GOPALA KRISHNA
ADE/400KV/APTRANSCO

2. Power Systems Protection -Introduction

3. Power Systems Protection -Introduction
Power Evacuation Substation
Transmission Substation
Switching Substation
Distribution Substation

4. Power System Components
1. Generators
2. Transformers
3. Transmission Lines
4. Feeders
5. Motors
6. Capacitor Banks
7. Bus Bars
8. Reactors
Power Systems Protection -Introduction

5. Power Systems Protection -Introduction
Why we need the Protection ?
¾ To detect abnormalities (faults).
¾ To eliminate such abnormality by
isolating smallest portion of the system
in a shortest period of time.
¾ To prevent injury to personnel.
¾ To prevent damage to Equipment.
¾ Enable Continuous service in
undamaged part of the network.

6. Power Systems Protection -Introduction
Protective Relay – What should it do ?
¾ Monitor system parameters continuously
(V, I, P, F)
¾ Operate quickly when necessary
(Dependability)
¾ Should not operate wrongly
(stability, discrimination)
To trip or not to trip ?

7. Power Systems Protection -Introduction
Protective System – What are the Requirements?
¾ Speed
The 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.
¾ Sensitivity
The 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.
¾ Selectivity
The 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.
¾ Reliability
The 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.

8. Power Systems Protection -Introduction
Protective Relay Scheme – What is it ?
¾ A Protective Relay
¾ CT / CVT / PT(EMVT)
¾ Auxiliary Power Supply (24 V to 240 V AC/ DC)
¾ Switching Device ( Breaker/ Isolator / Contactor)
¾ Trip Coil
¾ Alarm / Trip contact
¾ Control Wiring

9. Power Systems Protection -Introduction
Power System - Faults
Current
Over Load
Over Current
Earth Fault
Current Unbalance
Dir. Over Current
Dir. Earth Fault
Voltage
Over Voltage
Under Voltage
Voltage Unbalance
Neutral shift
Frequency
Over Frequency
Under Frequency
dF/dT
Power
Active power
Reactive power
Over power
Under power
Reverse power
Computed
Over fluxing
Loss of field
Differential
Over Current
Restricted E/F
Under Impedance
Control/Management
Synchronising
Load sharing
Islanding
Load shedding
DC Relays

10. Power Systems Protection -Introduction
Protection – ANSI Codes
Code numbers
Used to denote
Protections
On a SLD

11. Power Systems Protection -Introduction
Power System – Fault Handling
Trip & Isolate
Breaker is tripped on fault
Faulty section is isolated
Control & Regulate
Breaker is not tripped
Corrective actions
Generated on line

12. Power Systems Protection -Introduction
Relay operation when a fault occurs
¾ Each Relay should Protect a specific
Zone in the System.
¾ If fault is inside its Zone, Relay should
operate and isolate the faulted Zone.
¾ If fault is outside zone, Relay should
not operate,
Some other Relay should operate and
isolate

13. Power Systems Protection -Introduction
What happens when a fault occurs
¾ Fault current flows through number of
Relays.
¾ Some of these Relays will start to
operate.
¾ Only one Relay related to particular fault
should trip and interrupt the fault
current.
¾ Remaining Relays will reset after above.

14. Power Systems Protection -Introduction
Protection Relays – Inputs / Out puts
Inputs
Current CTs
Voltage PTs
Frequency PTs
Power CTs + PTs
Outputs
Trip Contact

15. Power Systems Protection -Introduction
Protection Relays – Settings
Pick up setting Low set
Highset
Time delay setting Definite time
Inverse time
% of CT
Rating
TMS
Setting

16. Power Systems Protection -Introduction
Power System – Trip time characteristics
I/Is
t
10
1.3 or
3.0 sec
I/Is
1.4
LS

17. Power System – Trip time characteristics
I/Is
t
10
1.3 or
3.0 sec
50 msec
6
HS
1.4
LS
Power Systems Protection -Introduction

18. Typical Inverse Time Delays
Power Systems Protection -Introduction
0.71
0.96
1.50
1.93
2.70
4.50
13.50
Very Inverse 1.5 sec
2.29
2.54
3.00
3.33
3.87
5.03
10.13
Normal Inv 3 sec
0.99
1.10
1.30
1.44
1.68
2.18
04.39
Normal Inv 1.3 sec
TIME MULTIPLIER SETTING – TMS : 1.00
0.20
0.36
0.81
1.27
2.28
5.33
26.66
Extremely Inverse
I/Is=20
I/Is=15
I/Is=10
I/Is=8
I/Is=6
I/Is=4
I/Is=2

19. Application
SLD representation
Front panel Controls
Back Panel terminations
Inputs / Outputs / Ratings
Settings (Inside)
Settings (on front panel)
Installation & wiring
Commissioning
Testing (Front panel)
Testing (SCITS)
Cat . No.
Things you should know
Power Systems Protection -Introduction

20. EVALUATION
OF
PROTECTIVE
RELAYS
PREPARED BY
GOPALA KRISHNA PALEPU
ADE/MRT(PROTECTION)

21. 1 ST GENERATION
FIRST 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.

22. 1 ST GENERATION
NEXT 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.

23. 2 ND GENERATION
SECOND GENERATION RELAYS :
STATIC RELAYS WITH TRANSISTORS
In 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.

24. 2 ND GENERATION
NEXT MODIFICATION :
STATIC RELAYS ON SINGLE PCB
IN 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.

25. 3 ND GENERATION
THIRD GENERATION RELAYS :
STATIC RELAYS WITH ICs
IN 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.

26. 3 ND GENERATION
NEXT MODIFICATION :
SEMI NUMERIC RELAYS
IN 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.

27. 4 ND GENERATION
MICROPROCESSOR BASED NUMERICAL RELAYS
¾ IN 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.

28. MICROPROCESSOR BASED RELAYS
¾ BACK GROUND WORK
¾ ADVANTAGES & DISADVANTAGES
¾ OPERATIONS & ALGORITHMS IN
MICROPROCESSOR
¾ FUNCTIONAL BLOCKS & OTHER HARDWARE OF
MICROPROCESSOR BASED RELAY
¾ FILTERING TECHNIQUES
¾ TESTING OF MICROPROCESSOR RELAYS

29. MICROPROCESSOR BASED RELAYS - BACKGROUND WORK
1960s
¾ A FEW CONCEPTS WERE PROPOSED
¾ HARDWARE WAS VERY EXPENSIVE
¾ BENEFITS OF MICROPROCESSORS FOR RELAYS
WERE NOT CLEAR
¾ IEEE ARTICLE “FAULT PROTECTION WITH A
DIGITAL COMPUTER” OUTLINED THE
FEASIBILITY & PROBLEMS ASSOCIATED IN S/S
PROTECTION WHEN A DIGITAL COMPUTER IS
USED.

30. MICROPROCESSOR BASED RELAYS - BACKGROUND WORK
1970s
¾ TWO PAPERS WERE PUBLISHED
“DIGITAL CALCULATION OF IMPEDANCE FOR TRANSMISSION
LINE PROTECTION”
“ 3 PH TRANSMISSION LINE PROTECTION WITH A DIGITAL
COMPUTER”
¾ PROMINENT MANUFACTURERS LIKE WESTINGHOUSE, IBM
STARTED INVESTIGATING S/S COMPUTER SYSTEMS
¾ PHILADELPHIA ELECTRIC & GE INITIATED PROJECTS ON
DIGITAL TECHNIQUES FOR PROTECTION
¾ VARIOUS ALGORITHMS WERE DERIVED FOR DIGITAL
CALCULATION OF PROTECTION PARAMETRS
¾ EXPERIMENTAL SYSTEMS WERE BUILT BY GE &
WESTINGHOUSE TO CHECK ALGORITHMS
¾ FIRST GENERATION OF MICROPROCESSOR BASED RELAYS
BUILT

31. MICROPROCESSOR BASED RELAYS - BACKGROUND WORK
1980s
¾ MAJOR MANUFACTURERS LIKE ABB, GE, GEC , TOSHIBA,
SIEMENS START DESIGN & SALES OF BROAD RANGE OF
PRODUCTS FOR POWER SYSTEM PROTECTION
¾ MICROPROCESSOR IMPROVES PERFORMANCE SPECS FOR
OPERATION IN INDUSTRIAL ENVIRONMENT
¾ MANY PLC BASED SYSTEMS ARE COMMISSIONED IN INDIA BY
L&T, SIEMENS, ECIL ETC.
¾ MANY ELECTRICITY BOARDS & PROCESS PLANTS IN INDIA
START USING MICROPROCESSOR BASED INSTRUMENTS
¾ THE WORD SCADA GETS POPULAR IN INDIA
¾ PGCIL GOES IN FOR MICROPROCESSOR BASED DISTANCE
RELAYS IN INDIA

32. MICROPROCESSOR BASED RELAYS - BACKGROUND WORK
1990s
¾ ABB & GEC ALSTOM INTRODUCED RANGE OF
MICROPROCESSOR BASED RELAYS FOR ALL UNIT
PROTECTIONS
¾ MAJOR MANUFACTURERS LIKE ABB, GE, GEC , TOSHIBA
STARTS DESIGN & SALES OF BROAD RANGE OF PRODUCTS
FOR POWER SYSTEM PROTECTION
¾ MANY ELECTRICITY BOARDS & PROCESS PLANTS IN INDIA
START USING MICROPROCESSOR BASED INSTRUMENTS
¾ PGCIL GOES IN FOR MICROPROCESSOR BASED DISTANCE
RELAYS IN INDIA
¾ MICROCONTROLLERS / DSPs ARE INTRODUCED IN LATE 90s
BY HARDWARE MANUFACTURERS WHICH HAVE IMPROVED
THE SPEED OF OPERATION.

33. PARAMETER NUMERIC CONVENTIONAL
ACCURACY 1% 5% / 7.5%
BURDEN < 0.5 VA > 5 VA
SETTING RANGES WIDE LIMITED
MULTI FUNCTIONALITY YES NO
SIZE SMALL LARGE
FIELD PROGRAMMABILITY YES NO
PARAMETER DISPLAY YES NO
SYSTEM FLEXILBILITY YES NO
CO-ORDINATION TOOLS MANY TWO
COMMUNICATION YES NO
REMOTE CONTROL YES NO
SPECIAL ALGORITHMS MANY LIMITED
SPECIAL PROTECTIONS YES NO
SELF DIAGNOSTICS YES NO
ADVANTAGES OF NUMERIC RELAYS

34. DIS-ADVANTAGES OF NUMERIC RELAYS
SOFTWARE INTENSIVE
OBSOLESENCE RATE
EMI / EMC PROBLEMS
SERIAL NATURE

35. PROTECTION ALGORITHM
MEASUREMENMT METHOD
TRIP TIME CALCULATION
GOOD FILTERING CHARACTERISTIC
(HARMONICS, NOISE, DC SHIFT)
FAST TRIP DECISION

36. FUNCTIONAL BLOCKS OF A NUMERIC RELAY
ANALOG
INPUT
SU-SYSTEM
DIGITAL
INPUT
SUB-SYSTEM
POWER SUPPLY
MICRO
PROCESSOR
COMMUNICATION
INTERFACE
RAM
ROM
EPROM
FLASH
DIGITAL
OUTPUT
SUB-SYSTEM
D
S
P

37. ANALOG INPUT SUB SYSTEM
CT
PT
SURGE
SUPPRESSION
SURGE
SUPPRESSION
ANALOG
FILTER
ANALOG
FILTER
MUX A / D
CONVERTER
MICRO
PROCESSOR

38. MICROPROCESSORS Vs MICRO CONTROLERS
C
O
N
T
R
O
L
C
O
N
T
R
O
L
Accumulator
Arithmetic Logic
Unit
Data Register
Address Register
Data Register
Arithmetic Logic
Unit
Address Register
Accumulator
I/O
ROM
RAM
EPROM
Timers
Counters
UART
Microprocessor Micro controller

39. RELAY HARDWARE
NORMALLY 400KV RELAYS SUPPLIED WITH FOLLOWING
CONFIGUARATION/HARDWARE
1. MIN 4Nos MAX 8Nos COMMAND/TRIP OUTPUTS
2. MIN 24Nos SIGNAL OUTPUTS
3. MIN 14 LED INDICATIONS
4. MIN 24 BINARY INPUTS
PC
MODEM
IRIG-B
RE/CC
16 / 32 BIT

40. 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.

41. 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.

42. 4 ND GENERATION
¾ 1ST DEVELOPMENT:
SOFTWARE DEVELOPMENT IS APPLICATION BASED
RELAYS i.e EACH PROTECTION FUNCTION HAVING
SEPARATE SOFTWARE & HARDWARE.
¾ Example:
1. LINE PROTECTION,
2. TRANSFORMER PROTECTION,
3. BUSBAR PROTECTION,
4. GENERATOR PROTECTION
5. MOTOR PROTECTION
6. REACTOR PROTECTION
7. CAPACITOR PROTECTION

43. 4 ND GENERATION
¾ 2ND 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.
¾ Example:
ABB: 1. REX 5xx SERIES FLATFORM
2. REX 316 SERIES FLATFORM
3. REX 670 SERIES FLATFORM
4. RED 500 SERIES FLATFORM
5. RED 600 SERIES FLATFORM

44. 4 ND GENERATION
¾ 3RD DEVELOPMENT:
UNIVERSAL SOFTWARE FOR ALL TYPES OF RELAYS
FOR PARTICULAR MANUFACTURER. i.e. ONE
SOFTWARE ONE MANUFACTURER.
¾ Example:
1. SIEMENS: SIPROTEC SERIES – DIGSI
2. GE MULTILIN: ENERVISTA
3. AREVA : MICOM S1

45. 4 ND GENERATION
¾ 4TH 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.
¾ Example:
1. GE MULTILIN: UR SERIES & SR SERIES

46. 4 ND GENERATION
¾ 5TH DEVELOPMENT:
EACH MANUFACTURER ADOPTING THEIR
PROPERITIERY BASED PROTOCOL FOR
COMMUNICATION, INTERFACING, NETWORKING AND
AUTOMATION. SOME UTILTIES ARE REQUESTED
MANUFACTURERS TO SUIT THEIR ADOPTED
PROTOCOL.
¾ Example:
1. UCA – Utility communication architecture
2. LON
3. SPA
4. PROFIBUS
5. MODBUS
6. DNP
7. FIELDBUS
8. MVB
9. IEC 60870

47. 4 ND GENERATION
¾ 6TH DEVELOPMENT:
BASED ON THE EXPERIENCE WITH DIFFERENT
PROTOCOLS, NEED FOR UNIFORMITY AND KNOW –
HOW FOR GLOBAL CONSIDERATION
ONE WORLD
ONE TECHNOLOGY
ONE STANDARD
A 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

48. BENIFITS OF UNIVERSAL PROTOCOL
Innovation & Expansion
¾firm rules for the description of new
data- objects and functions
¾Interoperability is maintained
Efficient maintenance
¾ robust data modelling
¾ self-descriptive equipment
¾ automation-configuration in XML
Separation from Application &
Communication
¾data and application stay secure
¾independent from communication
systems
¾unconstrained further development of
the technology
Quicker project execution
¾ comprehensive data model
¾ clear, standardised project-
and equipment description
¾ Configuration of substation in XML
ETHERNET & TCP/IP
¾Adopted worldwide
¾Scalable technology
¾Common use of infrastructure
One Protocol
¾ for all the needs in the substation
¾ flexible configuration
¾ no gateways required

49. INTEROPERATABULITY WITH ABB, AREVA & SIEMENS

50. TECHNOLOGY COMPARISION
Freely Configurable
Fixed
Fixed
Contacts &
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
Counters
Static Timers
Mechanical 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
LEDs
Flags, Targets
Visual Indication
NUMERICAL
STATIC
ELECTROMECHANICAL
SUBJECT

51. TECHNOLOGY COMPARISION
Possible
Not Possible
Not Possible
Multiple
Characteristics
Possible
Not Possible
Not Possible
Multiple
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 Compact
Modular, Compact
Bulky
Hardware Size
Human Machine
Interface, Softwares
Thumb Wheel,
Potentiometers, DIP
Switches
Plug Setting, Dial
Setting
Parameter
Setting
Available
Not Possible
Not Possible
Sequence of
Events
Available
Partially Available
Not Available
Self Supervision
Available & Freely
Configurable
Not Available
Not Available
Binary Input &
Output
NUMERICAL
STATIC
ELECTROMECHANICAL
SUBJECT

52. TECHNOLOGY COMPARISION
Extension and New
development
Possible and Open
Architecture
Fixed
Fixed
Solution
Stored In Memory
Not Possible
Not possible
Fault History
Protection Control &
Monitoring
Protection &
Monitoring
Only Protection
Protection
Control &
Monitoring
Possible
Not Possible
Not Possible
Service value
Indication
Inbuilt
External Hardware
External Hardware
Disturbance
Recording
Wide
Moderate
Limited
Range of
Settings
Lower
Lower Than
Electromechanical &
Moderate
Higher
Burden on CTs,
PTs & CVTs
Available
Not Possible
Not Possible
Communication
facility
NUMERICAL
STATIC
ELECTROMECHANICAL
SUBJECT

53. Relay ANSI Numbers (IEEE C37.2)
Carrier or Pilot wire Receive Relay
85
Inst Over-Current Relay
50
Operating Mechanism
84
M/C or T/F Thermal Relay
49
Trip circuit supervision Relay
95
Over-Voltage Relay
59
Over-Flux Relay
99
Voltage / Current balance Relay
60
Isolator or Disconnector
89
Exciter or DC Generator Relay
53
Voltage Directional Relay
91
Power Factor Relay
55
Voltage or Directional Power Relay
92
Field Application Relay
56
Differential Relay
87
AC Circuit Breaker
52
Lockout/Tripping Relay
86
AC IDMT Over-Current Relay
51
Automatic selective control or Transfer Relay
83
Negative phase sequence Relay
46
AC Auto Reclosure Relay
79
Under Current / Power Relay
37
Frequency Relay
81
Field failure (loss of excitation)
40
Density Switch or Sensor
61
Time delay relay
2
Pressure Switch
63
Interlocking relay
3
Phase Angle measuring or out of step Relay
78
Directional Power Relay
32
DC Over-Current Relay
76
Annunciation relay
30
Directional Over Current Relay
67
Volts per Hertz Relay
24
Blocking/Locking Relay
68
Synchronism Check Relay
25
Restricted Earth Fault Relay
64
Distance Relay
21
Alarm Relay
74
Isolating Contactor
29
DC Circuit Breaker
72
Under Voltage Relay
27
DEVICE
NUMBER
DEVICE
NUMBER