1. Power System Protective Relaying-Part One
Wei-Jen Lee, Ph.D., PE
Professor of Electrical Engineering Dept.
The Univ. of Texas at Arlington
Tel:

2. Introduction
Nature Cause

3. Introduction
Equipment Failure

4. Introduction
Human Error

5. 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)

6. 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)

7. Typical Protective Relays

8. Portable Protective Relay Test Equipment

9. Typical Power Circuit Breakers

10. Typical Power Circuit Breakers

11. 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

12. Typical Relay and Circuit Breaker Connections
Typical single line AC connection

13. Typical Relay and Circuit Breaker Connections
Typical three-phase AC connection

14. Basic Objectives of System Protection
Reliability
Selectivity
Speed of Operation
Simplicity
Economics

15. Factors Affecting the Protection System
Economics
Personality
Location of Disconnecting and Input Devices
Available Fault Indicators

16. Classification of Relays
Protective Relays
Regulating Relays
Reclosing, Synchronism Check, and Synchronizing Relays
Monitoring Relays
Auxiliary Relays
Others

17. 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

18. 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

19. Principles of Relay Application
Typical relay primary protection zones

20. Principles of Relay Application
Overlapping protection zones

21. 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

22. Information for Application
System fault study
Maximum loads and system swing limits
Current and voltage transformer locations, connections, and ratios
Future expansion