Power System Protective Relaying-Part One

Power System Protective Power System Protective Relaying-Part OneRelaying-Part One

Wei-Jen Lee, Ph.D., PE

Professor of Electrical Engineering Dept.

The Univ. of Texas at Arlington

Tel: 817-272-5046

E-mail: [email protected]

IntroductionIntroduction

Nature Cause


Equipment Failure


Human Error


Relay:an electric device that is designed to respond to input conditions in a prescribed manner and , after specified conditions are met, to cause contact operation or similar abrupt change in associated electric control circuits. (IEEE)


Protective Relay:A relay whose function is to detect defective lines or apparatus or other power system conditions of an abnormal or dangerous nature and to initiate appropriate control circuit action. (IEEE)

Typical Protective RelaysTypical Protective Relays

Portable Protective Relay Test Portable Protective Relay Test EquipmentEquipment

Typical Power Circuit BreakersTypical Power Circuit Breakers

Typical Power Circuit BreakersTypical Power Circuit Breakers

Sample Device NumbersSample Device Numbers

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

Typical Relay and Circuit Typical Relay and Circuit Breaker ConnectionsBreaker ConnectionsTypical single line AC connection

Typical Relay and Circuit Typical Relay and Circuit Breaker ConnectionsBreaker ConnectionsTypical three-phase AC connection

Basic Objectives of System Basic Objectives of System ProtectionProtectionReliabilitySelectivitySpeed of OperationSimplicityEconomics

Factors Affecting the Protection Factors Affecting the Protection SystemSystemEconomicsPersonalityLocation of Disconnecting and Input

DevicesAvailable Fault Indicators

Classification of RelaysClassification of Relays

Protective Relays Regulating Relays Reclosing, Synchronism Check, and

Synchronizing Relays Monitoring Relays Auxiliary Relays Others

Protective Relay PerformanceProtective Relay Performance

Since many relays near the trouble area may begin to operate for any given fault, it is difficult to completely evaluate an individual relay’s performance.

Performance can be categorized as follows:– Correct: (a) As planned or (b) Not as planned

or expected.– Incorrect: (a) Fail to trip or (b) False tripping– No conclusion

Principles of Relay ApplicationPrinciples of Relay Application

The power system is divided into protection zones defined by the equipment and available circuit breakers. Six possible protection zones are listed below:– Generators and generator-transformer units– Transformers– Buses– Lines (Transmission, subtransmission, and distribution)– Utilization equipment– Capacitor or reactor banks


Typical relay primary protection zones


Overlapping protection zones

Information for ApplicationInformation for Application

One line diagram and system configuration

Impedance and connection of the power equipment, system frequency, system voltage, and system phase sequence

Existing protection and problems Operating procedure and Practices Importance of the system equipment

being protected

Information for ApplicationInformation for Application

System fault study Maximum loads and system swing limits Current and voltage transformer locations,

connections, and ratios Future expansion

Documents

Power System Protective Relaying-Part One