System protection is used to detect problems in power system components and isolate faulty equipment to maintain reliable power. The key elements of a protection system include differential relays to protect generators and transformers from internal faults, overcurrent and distance relays to protect transmission lines from external faults, and bus differential relays to protect distribution buses. Protective devices are needed to maintain acceptable operation, isolate damaged equipment, and minimize harm to personnel and property.

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.