CIRCUIT BREAKERS | S.G.P ppt 3rd Year EEE | UNIT 1 Arc Interruption Theory (or) Arc Quenching (or) Arc extinction. Classification of circuit Breakers. Types of oil C.B Types & operation of SF₆ Circuit Breaker.

1. Switchgear and Protection
UNIT - 1

2. Arc Interruption Theory (or)
Arc Quenching (or) Arc extinction:
Methods:-
i. High resistance method:
• Resistance increases “many times”.
• Arc resistance increased by “lengthening or cooling”.
ii. Low resistance(or) zero interruption
method

3. Active Recovery voltage
Arc voltage
Energy Balance Theory (Cassie’s theory)
Generated Heat < Dissipated Heat
i. Removal of heat by cooling, lengthening and
Splitting arc.
 Voltage rate Theory
i. Arc interrupted by-removal of ions by recombining
them into neutral molecules.

4. Two Theories:
1)Energy balance theory
2)Voltage rate theory (slepins’ theory)
Terms:
i. Restriking voltage: voltage across breaking contact at
the instant of arc extinction.
ii. Recovery voltage: voltage appear after complete
removal of transient oscillations & final extinction of arc.

5. Loss less ideal system:-

7. Rate of rise of Restriking voltage:
peak value of restriking voltage
=
time taken to reach peak value
di Vc + c d²Vc
dt L dt²

8. Recovery Rate Theory
(or) Slepian’s Theory:
Removal of electrons & ions in two ways
i. Recombining them into neutral.
ii. Sweeping them away.

9. Limitations of slepian’s theory:
1. Assumptions restriking voltage and dielectric strength are
comparable.
2. Energy relation not considered.
3. Incomplete phase is not considered.
4. Restriking voltage and increase & increase in dielectric
strength as independent is not acceptable.
Energy balance theory (cassie’s theory):
• Theory explains, how are extinguished when heat of removal
b/w
contacts is lower than the rate at which heat is generated.
• Rate of generated heat < rate of removal of heat.
• Current zero instant, restriking voltage will be zero,
power will be zero power.

10. Energy balance theory Graph:

11. Classification of circuit Breakers:
1) Oil C.B: oil as insulating medium.
2) Air blast C.B:- High pressure air blast as medium.
3) Vacuum C.B:- vacuum for arc extinction.
4) Sulpher hexa:- Fluoride C.B:- SF ₆ as medium.
Oil C.B:-
 hydrogen gas produced.
 oil pushed away the arc & expanding hydrogen gas
bubble.

12. Arc extinction:
i. hydrogen gas at high pressure cools the arc.
ii. The gas rests up turbulence in the oil

13. Advantages:-
i. Absorbs arc energy, have excellent cooling property.
ii. Acts as insulator
iii.Surrounding oil preset cooling surface.
Disadvantages:
i. inflammable.
ii. Explosive mixture
iii.Replacement of oil

14. Types of oil C.B:
i. B.O.B.B:-
a) Plain oil c.b
b) Arc control oil c.b
ii. Minimum oil c.b (or) low oil c.b

15. Plane break oil c.b:
i. hydrogen gas bubble cools arc
ii. Pressurized gas eliminates the arc
iii. Arc length increases - resistance increases
– arc extinguished

16. Arc control oil C.B:
i. Self blast oil C.B:
“pressure generated by arc it self “ so called self
generated pressure oil C.B
ii. Forced blast oil C.B

17. Plain explosion pot:

18. Cross jet explosion pot:

19. Self compensated explosion pot:

20. Air Circuit Breaker , Air Blast Circuit Breaker:
Medium voltage c.b replaced by o.c.b
Up to 15kv good to avoid fire
Increase voltage by cooling arc , lengthening splitting.
Types of ACB:-
i. Plain air circuit breaker
ii. Air blast circuit breaker  up to 245kv & 420kv

21. Operation of ACB

22. Advantages:-
1. Risk of fire elimination
2. Oil replace avoided
3. Educe size
4. Less burning of contacts
5. Independent of current
Disadvantages:-
1. Very sensitive
2. Maintenance for compressor
Application:-
Beyond 110KV

23. Air blast circuit breaker
1. Axial blast ACB 2. Axial blast ACB with side moving contact
→ air blast directed along arc → air radially

24. 3. Cross blast ACB
→air right angles to arc

25. Resistance Switching:-

26. Three problems in air c.b:-
1. Current chopping

27. 2. Capacitive current breaking
3. Restriking voltage

28. Vacuum circuit breaker (or) VCB &
Vacuum Interrupter:
Operation of Vacuum circuit breaker:-

30. Advantages
i) Compact ii) Reliable iii0 Longer life
iv) No fire v) no gas vi) Low maintenance
vii) Quick operation viii) Low arc energy
ix) Low inertia x)small power for controlling machines
Applications:-
22kv to 66kv
60 to 100MVA
Appliations are in rural areas.

31. Types & operation of SF₆ Circuit Breaker
SF₆ circuit breaker:- (345KV)

32. Working:-
Types of SF₆ circuit breaker
1. Single interrupter SF₆ CB applied for up to 245 KV (220kv)system.
2. Two interrupter SF₆ CB applied for up to 420KV(400kv) system.
3. Four interrupter SF₆ CB applied for up to 800KV(715kv) system.

34. Working of SF₆ circuit breaker:

35. Advantages :
1. noiseless no exhaust
2. no moisture
3. no fire (non inflammable)
4. low maintenance
5. light foundation
6. minimum auxiliary equipment
7. 2 to 3 times than air dielectric strength, so
can interrupt large current.
Disadvantages:
1. Costly
2. Additional equipment for reconditioning

36. Applications:
1. Up to 60kv
2. Voltages 50 to 80kv
3. Developed for 115kv to230kv
4. Power rating 10MVA to 20MVA
5. Interruption time less then 3 cycles

37. Simple SF₆ Diagram:

38. Circuit breaker ratings:
Breaking capacity:
Making capacity :
= 2.55 X symmetrical breaking capacity
Short time rating:

40. Various duties of Circuit breaker:-

41. Faults occurrence and types: