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. of Texas at Arlington Tel: 817-272-5046 E-mail: [email protected]

Introduction  Nature

Cause

Introduction  Equipment

Failure

Introduction  Human

Error

Introduction  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)

Introduction  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 Relays

Portable Protective Relay Test Equipment

Typical Power Circuit Breakers

Typical Power Circuit Breakers

Sample 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 Breaker Connections  Typical

single line AC connection

Typical Relay and Circuit Breaker Connections  Typical

three-phase AC connection

Basic Objectives of System Protection  Reliability  Selectivity  Speed

of Operation  Simplicity  Economics

Factors Affecting the Protection System  Economics  Personality  Location

of Disconnecting and Input

Devices  Available Fault Indicators

Classification of Relays  Protective

Relays  Regulating Relays  Reclosing, Synchronism Check, and Synchronizing Relays  Monitoring Relays  Auxiliary Relays  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  Maximum loads and system swing limits  Current and voltage transformer locations, connections, and ratios  Future expansion