1-Power System Protective Relaying-Part One

7/28/2019 1-Power System Protective Relaying-Part One

1/36

1/27/201

Power System Protective RelayingPower System Protective Relaying

2

The purpose of network protectionequipment is tominimize the effects of faults, which cannever be entirely avoided, on an electricalpower system.

IntroductionIntroduction


2/36

1/27/201

Power Systems-Fault Free

Not PossibleMany Reasons

3

4

Power system Protection Engineering isan important component of the electricalplant system and of decisive significancefor the reliable and safe operation of apower system .


3/36

1/27/201

5

The cause of electric power system faults

is insulation breakdownThis breakdown can be due to a variety of different factors:

Lightning. wires blowing together in the wind. animals or plants coming in contact with

the wires.

salt spray or pollution on insulators.

6

Tree limbs falling on the lineInsulation deteriorationVandalism


4/36

1/27/201

Nature Cause


Equipment Failure


5/36

1/27/201

Substation FailureSubstation Failure

The AftermathThe Aftermath


6/36

1/27/201

Results of TransformerResults of Transformer FireFire

Generator FaultGenerator Fault


7/36

1/27/201

Expensive Consequences forExpensive Consequences for

Protection FailureProtection Failure


Human Error


8/36

1/27/201

IntroductionIntroductionRelay: an electric device that isdesigned to respond to inputconditions in a prescribed mannerand , after specified conditions aremet, to cause contact operation orsimilar abrupt change in associated

electric control circuits. (IEEE)


Protective Relay: A relay whosefunction is to detect defective linesor apparatus or other power systemconditions of an abnormal ordangerous nature and to initiate

appropriate control circuit action.(IEEE)


9/36

1/27/201

What is RelayingDetects abnormal conditionsInitiate Corrective actionsHas fast responseDisrupts only essential and minimum

area

RequirementsDefine the undesirable conditionsRemove only the faulted equipmentand to maintain the un-faultedportion of the system.


10/36

1/27/201

Power System ProtectionScience, skill and art of applying andsetting relays &fuses to maximumsensitivity to detect disturbances and toavoid the operation on all permissibletolerable conditions

Define and understand Power SystemfaultsMeasure and Monitor systemparameters V, I, f through transducers(Current, potential transformers)Detection schemes RelaysAction Equipment Circuit Breakers


11/36

1/27/201

21

Effects of faults on power systemEffects of faults on power system

Flow of excessive currentAbnormal voltagesVoltage elevation of system neutralInduce over voltages on neighbouringequipments .

Hazards to human, equipment andanimals.

22

Need for fault analysisNeed for fault analysis

Design of protection system requires theknowledge of fault current.The information obtained from thefault studies are used:to select the sizes of circuit breaker,fuse and characteristic, setting of relays.


12/36

1/27/201

23

Types of faultTypes of fault

Symmetrical fault :Usually three phase to ground fault

Unsymmetrical (Asymmetrical) faultThe fault is unbalanced in nature

24

Sources of Asymmetrical fault areSources of Asymmetrical fault are

One phase open circuit

Unbalanced in load mainly the arc loads


13/36

1/27/201

25

One phase open circuit

26


14/36

1/27/201

27

SLG fault

28

Sources of Asymmetrical fault are:Sources of Asymmetrical fault are:


15/36

1/27/201

Typical Protective RelaysTypical Protective Relays

Portable Protective Relay TestPortable Protective Relay TestEquipmentEquipment


16/36

1/27/201

RelaysRelaysA relay is a low-powered device usedto activate a high-powered device.Relays are used to trigger circuitbreakers and other switches insubstations and transmission anddistribution systems.

31

Relay CharacteristicsRelay Characteristics

ReliabilityProbability to function properly.The ability to operate fordisturbances within zone(dependability)The ability to refrain from operationfor external abnormalities( security)


17/36

1/27/201

SensitivityAbility to detect abnormal quantities

SelectivityAbility to obtain the desired

operation to avoid unnecessarytripping

SpeedAbility to initiate operation in theshortest time possible


18/36

1/27/201

EconomyThe ability to function at minimumcost

SimplicityAbility to function and to operatewith minimum equipment andcircuitry

36

Substation control panel relays


19/36

1/27/201

37

Relay and control panel

High Voltage FusesHigh Voltage Fuses

High voltage fuses are used toprotect the electrical system in asubstation from power transformerfaults.They are switched for maintenanceand safety.

38


20/36

1/27/201

39

High voltage fuses in a switch box

40

External switch for high voltage fuses


21/36

1/27/201

Typical Power Circuit BreakersTypical Power Circuit Breakers

42

Air circuit breaker


22/36

1/27/201

43

Vacuum circuit breaker, inside

44

Vacuum circuit breaker, outside


23/36


24/36

1/27/201

47

SF6 gas power circuit breaker

48

SF6 gas power circuit breaker


25/36

1/27/201

Typical Power Circuit BreakersTypical Power Circuit Breakers

Sample Device NumbersSample Device Numbers

Master element: 1Time-delay starting or closing relay: 2Distance relay: 21Directional power relay: 32Instantaneous overcurrent relay: 50AC time overcurrent relay: 51AC directional overcurrent relay: 67Frequency relay: 81Differential protective relay: 87


26/36

1/27/201

51

IEEE Device Numbers & Functions

52

Device Description Legend49 Thermal50/51 Instantaneous & Time Overcurrent51 Time Overcurrent51N-1 Ground Time Overcurrent51N-2 Neutral Time Overcurrent51N-3 Ground Time Overcurrent63 Sudden Pressure67 Directional Overcurrent67N Directional Ground Overcurrent86 Lockout Auxiliary87T Phase Differential, 3 Phase87N Ground Differential

OP Operating CoilPol Polarizing CoilN.C. Normally Closed

Transformer BushingCS Circuit SwitcherRg Grounding Resistor


27/36

1/27/201

Typical Relay and CircuitTypical Relay and CircuitBreaker ConnectionsBreaker Connections

Typical single line AC connection

Typical Relay and CircuitTypical Relay and CircuitBreaker ConnectionsBreaker Connections

Typical three-phase AC connection


28/36

1/27/201

Basic Objectives of SystemBasic Objectives of SystemProtectionProtection

ReliabilitySelectivitySpeed of OperationSimplicityEconomics

Factors Affecting the ProtectionFactors Affecting the ProtectionSystemSystem

EconomicsPersonalityLocation of Disconnecting and InputDevices

Available Fault Indicators


29/36

1/27/201

57

Philosophy of ProtectionPhilosophy of ProtectionBoth an art and a scienceWell-designed system will use: Overlapping primary zones of protection

Some form of backup protection

58


30/36

1/27/201

59

Qualities Required of ProtectionSelectivity (Discrimination): Effectivenessin isolating only the faulty part of thesystem.Stability: The property of remaininginoperative with fault occurring out sidethe protected zone (called externalfaults).

60

Speed of operation:The time between the incidence of a faultand the trip command being issued to thecircuit breaker by the protection.The speed of operation must be as fast aspossible.In modern power systems the relay

operates in one or fraction of a period of the power system frequency.


31/36

1/27/201

61

Sensitivity: The level of magnitude of the fault current at which theoperation of protective deviceoccurs. Reliability: The ability of a protectivesystem to fulfill its purposethroughout its operation life.

It should not mal-operate at anytime.

62

Economic of consideration:

In distribution system it is veryimportant and it overrides the technicalconsideration provided basic safetyrequirements are met.In transmission systems the technicalaspects are more important.


32/36

1/27/201

63

Zones of protectionZones of protection

Gen Zone

Transf Zone

Bus 1Zone

Line 1 Zone

B u s

2 Z o n e

Line 3ZoneLine 2Zone

64

Overlapping zonesOverlapping zones

Zones A and B overlap at circuit breaker CB Faults in overlap trip both zones No gaps in protection

Zone AZone BCB

Trip all zone A Trip all zone B

CT ACT B


33/36

1/27/201

Classification of RelaysClassification of RelaysProtective RelaysRegulating RelaysReclosing, Synchronism Check, andSynchronizing RelaysMonitoring RelaysAuxiliary Relays

Others

Protective Relay PerformanceProtective Relay Performance

Since many relays near the trouble areamay begin to operate for any given fault, itis difficult to completely evaluate anindividual relays performance.Performance can be categorized asfollows: Correct: (a) As planned or (b) Not as plannedor expected. Incorrect: (a) Fail to trip or (b) False tripping No conclusion


34/36

1/27/201

Principles of Relay ApplicationPrinciples of Relay ApplicationThe power system is divided into protectionzones defined by the equipment and availablecircuit breakers. Six possible protection zonesare listed below: Generators and generator-transformer units Transformers Buses Lines (Transmission, subtransmission, and distribution)

Utilization equipment Capacitor or reactor banks

Principles of Relay ApplicationPrinciples of Relay Application

Typical relay primary protection zones


35/36

1/27/201

Principles of Relay ApplicationPrinciples of Relay ApplicationOverlapping protection zones

Information for ApplicationInformation for Application

One line diagram and system configurationImpedance and connection of the powerequipment, system frequency, systemvoltage, and system phase sequenceExisting protection and problems

Operating procedure and PracticesImportance of the system equipment beingprotected


36/36

1/27/201

Information for ApplicationInformation for ApplicationSystem fault studyMaximum loads and system swing limitsCurrent and voltage transformer locations,connections, and ratiosFuture expansion

Documents

1-Power System Protective Relaying-Part One