2. Protective Relaying - Introduction
Requires knowledge of :
Equipments to be protected
Behavior of equipment
Faults in an equipment
Protection philosophies
Terminologies used
3. Protective Relaying - Introduction
Requires knowledge of :
IEEE notations
Protection schemes
Single line diagram
Symmetrical components
Electronics
Communication methods
4. Power System - Objective
• To generate and supply electrical energy to
the consumers - reliably and economically
• Better reliability can be achieved by
improved system design, allowing for
sufficient spare capacity, considering future
additions and/or expansions
5. Power Systems Protection -Introduction
Power System Components
1. Generators
2. Transformers
3. Transmission Lines
4. Feeders
5. Motors
6. Capacitor Banks
7. Bus Bars
9. Objectives of protection
Prevent deterioration by disconnecting
circuits & equipments subjected to :
• Overload
• Over-temperature
• Under-over voltages
• Unbalanced currents
• Under – over frequency
10. Objectives of protection
• Loss of field
• Loss of synchronization
• Anti-motoring
• Reverse power
• Reverse current
• Phase reversal &
• Open phase
11. Objectives of protection
Limit damage by disconnecting circuits
& equipments subjected to :
• Short circuits
• Earth faults
12. Power Systems Protection -Introduction
Protection – Purpose
• To detect abnormalities (faults)
• To eliminate such abnormality
- by isolating the smallest portion of the system
in the shortest period of time
• To prevent injury to personnel
• To prevent damage to equipment
13. 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)
14. Protective Relaying
Design of Protective Schemes
• General Philosophy
• Reliability (Dependability and Security)
• Sensitivity
• Speed of operation
• Economics
• Simplicity
16. The 4 ‘S’ of a Protection Scheme
• Selectivity: When a fault occurs, the
protection system is required to select and
trip only the nearest circuit breakers. This
property of selective tripping is also called
discrimination. This can either be a current
based discrimination or a time based
discrimination or a combination of both.
17. The 4 ‘S’ of a Protection Scheme
• Stability: This is the ability of the protection
system to remain inert to all load conditions
and faults external to the relevant zone of
the protection scheme. This is of particular
importance in Unit Protection Schemes
(e.g.) Differential Protection, REF
Protection, etc.
18. The 4 ‘S’ of a Protection Scheme
• Speed: The primary function of a
protection scheme is to detect and isolate
faults from a power system in a very short
time than which could be achieved
manually. This is to safeguard continuity of
supply to healthier portions, by removing
each disturbance , before it leads to wide
spread loss and/or plant shut downs.
19. The 4 ‘S’ of a Protection Scheme
• Sensitivity: This refers to the minimum
operating quantity requirements of a
complete protection system. A protection
system is said to be sensitive, if the
operating quantity is low. But, with respect
to individual relays, it is not the current or
voltage, but the VA consumption of the
relay at the minimum operating quantity.
20. Device Function Numbers (ANSI/IEEE Codes)
The devices in the switching equipment are denoted
by numbers, with appropriate suffix letters when
necessary, according to the functions they perform.
These numbers are based on a system adopted as
standard for automatic switchgear by IEEE and are
incorporated in American Standard (ANSI) C37.2-
1970.
This system is used in connection diagrams, in
instruction booklets and in specifications to designate
the relays and other devices to save text and space.
Power Systems Protection -Introduction
21. Protection – ANSI Codes
Code numbers
Used to denote
Protections
On a SLD
Power Systems Protection -Introduction
22. Zone of protection
The zone of protection of relay or
circuit breaker trip device is that
segment of the power system in
which the occurrence of assigned
abnormal conditions should cause the
protective device to operate
31. Protection
Primary Protection
First line of defence
Is responsible to protect the power system
elements from all types of faults
(e.g.- High speed differential relay,Instantaneous overcurrent relay)
Back-up Protection
Operates only if primary protection fails
(e.g.phase time overcurrent relay)
32. Power Systems Protection -Introduction
Protective Relay Scheme – What is it ?
• A protective relay
• CT / PT
• Auxiliary Power supply (24 V to 240 V AC/ DC)
• Switching device ( Breaker/ Contactor)
• Trip Coil
• Alarm / Trip contact
• Control Wiring
34. Inputs to Protective relays
OVER CURRENT RELAYS CURRENT
UNDER / OVER VOLTAGE RELAYS VOLTAGE
SYNCHRONISING RELAYS
FREQUENCY RELAYS
DISTANCE RELAYS CURRENT &
DIRECTIONAL RELAYS VOLTAGE
REVERSE POWER RELAYS POWER
SUDDEN PRESSURE RELAY PRESSURE
OVER TEMPERATURE RELAY TEMPERATURE
36. Comparing element or
Comparator
Comparison is made on the basis of
amplitude, relative phase or
combination of amplitude & relative
phase.
• Single input – Electromagnetic
• Multi input – Static
• Output – Mechanical torque /
Electrical signal
37. Control element
Operated in one direction or other by
the output of comparator and it
controls tripping of circuit breaker.
39. Protective relays - Terminology
SETTINGS
PICK UP
LOW SET
HIGH SET
TMS
STEPS
TIME DELAYS
INSTANTANEOUS
INVERSE TIME
DEFINITE TIME
RATINGS
CT
PT
AUX. POWER
BURDEN
CT INPUT
PT INPUT
DIRECT SEQUENCE
NEGATIVE SEQUENCE
ZERO SEQUENCE
VECTORS
CURRENT
VOLTAGE
IMPEDANCE
MACHINE RELATED
PERCENT. IMPEDANCE
FULL LOAD RATING
TIME CONSTANT
OVER LOAD CHAR.
SYSTEM
GROUNDED
UNGROUNDED
RESISTANCE GROUNDED
OPERATIONAL
MASTER TRIP
LOCK OUT
RESTRAINTS
INTER TRIP
BLOCKING
FLAG
SELF RESET
HAND RESET
MANUAL RESET
RELAY TEST
ANALYSIS
TRIP DATA
W/F CAPTURE
DIAGNOSTICS
CONNECTIONS
RESIDUAL
OPEN DELTA
CBCT
40. 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 O/C
Restricted E/F
Under Impedance
Control/Management
Synchronizing
Islanding
Load shedding
Power Systems Protection -Introduction
41. 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
Power Systems Protection -Introduction
42. 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 zone
• If fault is outside zone,
Relay should not operate –
Some other relay should operate and isolate
43. 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 should trip and
interrupt fault current
• Remaining relays will reset after above
44. Protection Relays – Inputs / Out puts
Inputs
Current CTs
Voltage PTs
Frequency PTs
Power CTs + PTs
Outputs
Trip Contact
Power Systems Protection -Introduction
45. Protection Relays – Settings
Pick up setting Low set
Highset
Time delay setting Definite time
Inverse time
% of CT
Rating
TMS
Setting
Power Systems Protection -Introduction
46. Power System – Trip time characteristics
I/Is
t
10
1.3 or
3.0 sec
1.4
LS
Power Systems Protection -Introduction
47. 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
48. TMS=1
I/Is=2 I/Is=4 I/Is=6 Is=8 I/Is=10 I/Is=15 I/Is=20
Normal Inv 3 sec 10.13 5.03 3.87 3.33 3 2.54 2.29
Normal Inv 1.3 sec 4.39 2.18 1.68 1.44 1.3 1.1 .99
Very Inverse 13.5 4.5 2.7 1.93 1.5 .96 .71
Extremely Inverse 26.66 5.33 2.28 1.27 0.81 0.36 0.20
Typical Inverse time delays
Power Systems Protection -Introduction
49. [ A]
t(I) = ---------------- * TMS
[(I/Is)a – 1]
Where,
t(I) = Trip Time in Seconds
I = Fault Current
Is = Set Current
TMS = Time Multiplier Setting
Power System – Trip time characteristics
Inverse time delays – General Algorithm
As per BS 142 & IEC 60255-4
Power Systems Protection -Introduction
50. Curve Name A a
Normal Inverse 1.3 Sec. 0.0613 0.02
Normal Inverse 3.0 Sec. 0.1414 0.02
Very Inverse 13.5 1
Extremely Inverse 80 2
Power System – Trip time characteristics
Inverse time delays – General Algorithm
Power Systems Protection -Introduction
51. User’s Expectations
Sense a fault &
Initiate trip contact CONVENTIONAL
Parameter display
Event record
Fault data record
Wave form record
Communication
Control logic
PRESENT DAY
NEEDS
52. Basic types of Relays
• Magnitude relay
• Directional relay
• Ratio relay
• Differential relay
• Pilot relay
56. Electromechanical relays
ADVANTAGES LIMITATIONS
WELL PROVEN(?) LARGE SIZE
LOW COST INACCURACY
SELF POWERED HIGH BURDEN
LARGE VARIETY
LIMITED PROTECTIONS
DIFFICULT TO CO-ORDINATE
NEED FOR EXTRA HARDWARE
INTROVERT IN NATURE
58. Solid state relays
ADVANTAGES LIMITATIONS
SMALL SIZE NO COST ADVANTAGE
LOW BURDEN HIGHLY NOISE PRONE
EASY TO MANUF DRIFT IN SETTINGS
INACCURACY
LARGE VARIETY
LIMITED PROTECTIONS
DIFFICULT TO CO-ORDINATE
NEED FOR EXTRA HARDWARE
LOW RELIABILITY
INTROVERT IN NATURE
59. Increase in system capacities
New problems to be handled
New utility conditions
Low factor of safety on equipments
Trip information / analysis
Co-ordination problems
Self diagnostic feature
Concept of “UNMANNED S/S”
Need for new technology
61. MICROPROCESSOR BASED RELAYS - BACKGROUND WORK
1960s
A 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
62. MICROPROCESSOR BASED RELAYS - BACKGROUND WORK
1970s
TWO 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
63. MICROPROCESSOR BASED RELAYS - BACKGROUND WORK
1980s
MAJOR MANUFACTURERS LIKE GE, ABB, 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
P[GCIL GOES IN FOR MICROPROCESSOR BASED
DISTANCE RELAYS IN INDIA
64. MICROPROCESSOR BASED RELAYS - BACKGROUND WORK
1990s
ABB & GEC ALSTOM INTRODUCE RANGE OF
MICROPROCESSOR BASED RELAYS FOR
ALLALL UNIT PROTECTIONS
MAJOR MANUFACTURERS LIKE GE, ABB, GEC , TOSHIBA
START 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.
65. MICROPROCESSOR BASED RELAYS - BACKGROUND WORK
1995
L&T COMES OUT WITH RANGE OF
MICROPROCESSOR BASED RELAYS
IN ASSOCIATION WITH
MICROELETTRICA SCIENTIFICA OF ITALY
ABB COINS THE WORD “NUMERIC RELAYS”
FOR ALL RELAYS WITH MICRO CONTROLLER
66. Micro-processor based relays
Offer best solution for present day relaying
due to following:
• Intelligent devices
• Can implement complex algorithms
• Oscillographic information
• Networking
• Multi – functions
• Self diagnostics
• User friendly
67. Numeric relays
- It is an improvement over relays with
Microprocessor
- Heart of the system is a micro-
controller
- Entire operation is based on handling
a set of 8 - bit numbers
68. Protective relays – Comparison
ELECTRO SOLID-STATE NUMERICAL
MECHANICAL
INPUT PEAK S/H CIRCUITS
SENSING COIL DETECTOR A/D CONVERTERS
SETTINGS TAPS ANALOG REF DIGTAL NUMBER
COMPARISON TORQUE ANALOG DIGITAL NUMBER
VOLTAGE
ALGORITHM/ RLC GAIN ADJ. ARITHMATIC
PARAMETER SCALAR SCALAR VECTORIAL
IDENTITY
OUT PUT PHYSICAL DRIVERS LOGIC ARRAY
69. 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
SPECIALALGORITHMS MANY LIMITED
SPECIAL PROTECTIONS YES NO
SELF DIAGNOSTICS YES NO
ADVANTAGES OF NUMERIC RELAYS
70. Numeric relays
ADVANTAGES OVER
ELECTROMECHANICAL RELAYS
1. FIELD PROGRAMMABILITY
2. PARAMETER DISPLAY
3. SYSTEM FLEXIBILITY
4. CO-ORDINATION
5. COMMUNICATION
6. REMOTE CONTROL
7. SPECIAL ALGORITHMS
8. SUPERIOR PROTECTION
74. FUNCTIONAL BLOCKS OF A NUMERIC RELAY
ANALOG
INPUT
SUB-SYSTEM
DIGITAL
INPUT
SUB-SYSTEM
POWER SUPPLY
MICRO
PROCESSOR
COMMUNICATION
INTERFACE
RAM
ROM
EPROM
FLASH
DIGITAL
OUTPUT
SUB-SYSTEM
D
S
P
75. ANALOG INPUT SUB SYSTEM
CT
PT
SURGE
SUPPRESSION
SURGE
SUPPRESSION
ANALOG
FILTER
ANALOG
FILTER
MUX A / D
CONVERTER
MICRO
PROCESSOR
76. DIGITAL SIGNAL PROCESSORS
Designed for repetitive measurements
Digital filtering
Highly suitable where microprocessor has to do
measurements, logic, communication and other functions
Designed to handle one instructions per clock cycle
(microprocessors need many clocks per instruction)
Improves speed of operation
DSP Types :
- Analog Devices 21XX family
- Texas Instruments TMS3XX family
- Motorola 56XXX family
77. MICROPROCESSORS Vs MICRO CONTROLERS
C
O
N
T
R
O
L
C
O
N
T
R
O
L
Accumulator
Arithmatic 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
78. TYPES OF MEMORY NUMERIC RELAYS
RAM Read / Write Memory. Used for temporary storage
of variables - like sampled data / oscillographic data
EEPROM / Electrically Erasable Programmable Read Only Memory
NOVRAM Non Volatile RAM
Used for storage of data that remains when power off
(CT/PT/machine ratings, trip settings etc.)
ROM Read Only Memory. Masked version used for high volume
production units. Used for storage of specific programmes.
EPROM Electrically Programmable ROM . Used as above.
Easy to programme and reprogram. Adaptable to changes.
FLASH New type of EPROM that can be programmed repeatedly.
EPROM Allows program updates in the field without changing chips.
79. 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 inputting 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.
80. FILTERS IN NUMERIC RELAYS
NEED FORE FILTERS
PROTECTIVE RELAYS MUST FILTER UNWANTED SIGNALS
AND HANDLE ONLY THOSE NEEDED FOR TRIP CALCULATIONS
Should be able identify and ignore :
- Switch yard noises
- Harmonics
- Exponentially decaying DC offsets
- CCVT Transients
- Reflections from travelling waves
- Capacitive series compensation
81. 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.
82. STANDARDS FOR RELAYS
• IS 3231 – 1986 Specification for electrical
relays for power system protection .
• IS 1885 – 1966 Electro-technical
PART IX Vocabulary, Electrical relays .
• BS 142 - 1966 Specification for electrical
protective relays.
• BS 3950 – 1965 Specification for electrical
protective system for a.c.plant .
• IS 8686 – 1977 Specification for static protective
relay.
• IS 9124 – 1979 Guide for maintenance and field
testing of relays .
83. STANDARDS FOR RELAYS
• IS 9124 – 1979 Guide for maintenance and
field testing of relays .
• IS 2705 Part I to IV Specification for
current transformers.
• IS 3156 Part I& II Specification for voltage
transformers .
• BS 3978 – 1973 Specification for current
transformers.
• IS 3842 1972 Application guide for elect.
relays
