1. Power System Protection

2. OUTLINE
 System protection-Definition
 Need for the protection
 Elements of the protection system

3. What is System protection?
 System protection is the art and science of detecting
problems with power system components and
isolating these components.

4. Need for the protection
 The power system must maintain acceptable
operation 24 hours a day
 Voltage and frequency must stay within certain
limits
 Protect the public
 Improve system stability
 Minimize damage to equipment
 Protect against overloads

5. Damage to Main Equipment

7. COMPONENTS USED FOR
PROTECTION

12. Components to be protected
 Generators
 Transformers
 Lines
 Buses
 Capacitors

13. GENERATOR PROTECTION

14. Generator Protection
 What can go wrong?
Stator Winding Problems
1. Winding-winding short

15.  How Do We Protect the Stator?
 A. Differential Protection (what goes in must come
out)
 1. Detects phase-phase faults

17. TRANSFORMER
PROTECTION

18. Transformer Protection
 What can go wrong?
● Winding-to-winding faults
● Winding-to-ground faults
● Bushing faults

19. Transformer Protection
 Protection Methods:
 Fuse
 Overcurrent
 Differential

20. FUSE

21. OVERCURRENT RELAYS

22. DIFFERENTIAL METHOD

23. TRANSMISSION LINE
PROTECTION

24. TRANSMISSION LINE PROTECTION
What Can Go Wrong?
 FAULTS (Short Circuits)
SOME CAUSES OF FAULTS:
 Trees
 Lightning
 Animals (birds, squirrels, snakes)
 Weather (wind, snow, ice)
 Natural Disasters (earthquakes, floods)
 Faulty equipment (switches, insulators, clamps, etc.)

26. TYPES OF FAULTS
 Single-Phase-Ground: 70–80%
 Phase-Phase-Ground: 17–10%
 Phase-Phase: 10–8%
 Three-Phase: 3–2%

28. How Do We Protect Transmission Lines?
 Overcurrent
 BiDirectional Overcurrent
 Distance (Impedance)
 Line Current Differential

29. OVERCURRET PROTECTION

30. DISTANCE PROTECTION
A distance relay measures the impedance of a line
using the voltage applied to the relay and the current
applied to the relay.
When a fault occurs on a line, the current rises
significantly and the voltage collapses significantly.
The distance relay (also known as impedance relay)
determines the impedance by Z = V/I. If the
impedance is within the reach setting of the relay, it
will operate.

32. RELAY PROTECTION

33. BUS PROTECTION
 Bus Differential:
 Current into bus must equal current out of bus

35. Capacitor Protection
 Purpose of capacitors: Shunt capacitors raise the
voltage on a bus or line to a higher level, thus helping
keep the voltage at desired level Series capacitors
cancel out the inductive reactance of a line, thus
making the line appear shorter increasing load flow
on the line.