Power System Protective Relaying-Part One

Power System Protective Relaying-Part One

Wei-Jen Lee, Ph.D., PE Professor of Electrical Engineering Dept. The Univ Univ.. of o f Texas Texas at Arlington Tel: 817-272-5046

Introduction 

Nature Cause

Introduction 

Equipment Failure

Introduction 

Human Error 

Introduction 

Relay:an electric device that is Relay:an 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)

Introduction 

Protective Relay:A 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 Relays

Portable Protective Relay Test Equipment

Typical Power Circuit Breakers

Typical Power Circuit Breakers

Sample Device Numbers 

Master element: 1

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Time-delay starting or closing relay: 2

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Distance relay: 21

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Directional power relay: 32

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Instantaneous overcurrent relay: 50

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AC time overcurrent relay: 51

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AC directional overcurrent relay: 67

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Frequency relay: 81

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Differential protective relay: 87

Typical Relay and Circuit Breaker Connections 

Typical single line AC connection

Typical Relay and Circuit Breaker Connections 

Typical three-phase AC connection

Basic Objectives of System Protection 

Reliability

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Selectivity

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Speed of Operation

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Simplicity

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Economics

Factors Affecting the Protection System 

Economics

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Personality

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Location of Disconnecting and Input Devices

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Available Fault Indicators

Classification of Relays 

Protective Relays

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Regulating Relays

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Reclosing, Synchronism Check, and Synchronizing Relays

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Monitoring Relays

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Auxiliary Relays

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Others

Protective 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 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

Principles of Relay Application 

Typical relay primary protection zones

Principles of Relay Application 

Overlapping protection zones

Information 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 Application 

System fault study

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Maximum loads and system swing limits

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Current and voltage transformer locations, connections, and ratios

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Future expansion