This document summarizes different types of switchgear and protection devices used in electrical circuits. It describes common elements like fuses, air break switches, knife switches, load interrupters, line isolators, and circuit breakers. Circuit breakers are classified based on their mediums like oil, air blast, SF6, and vacuum. Minimum oil, cross blast, and double pressure SF6 circuit breakers are explained in more detail regarding their components, advantages, disadvantages, and applications. The document concludes with a brief overview of overhauling circuit breakers.

1. Switch gear and protection
By
BhANU GANESH LUKKA
Asst.prof

2. SYLLABUS

5. The apparatus used for switching, controlling and protecting the electrical circuits
and equipment is known as switch gear.
 It is Used to de-energize the equipment
Switch Gear :
Elements of Switch Gear:
 Fuses
 Air break switches
 Knife switches
 Load interrupter
 Line isolator
 Circuit Breaker

6. Fuse :
It is a small piece of metal inserted in the circuit which melts when excessive current flow
through it and breaks the circuit.
 Temperature / heat Q = If
2 . r..t
 It operates only under abnormal conditions or fault conditions

7.  An “air break switch' is a switchgear device that uses air as the dielectric.
 Air Break Switches (ABS) are widely installed throughout distribution networks for use as both
isolation or switching points.
 These are usually employed in outdoor installations.
Air Break switch:

8. Knife switch:
A knife switch is a type of switch used to control the flow of electricity in a circuit. It is composed
of a hinge which allows a metal lever, or knife, to be lifted from or inserted into a slot or jaw.
 These are used in electrical laboratories
SPST SPDT
DPST
DPDT TPST TPDT

9. Load interrupter will be operate in order to reduce the overloads in the system
 It is operated only at full – load condition
Load interrupter:

10. Line Isolator:
 It is Used to provide more clearance for the system
 Operates only at No – Load condition

11. Circuit Breaker:
A circuit breaker is an equipment which can make or break a circuit under all conditions
i.e., No – Load, Full – Load and Fault conditions.

12. MCCB ELCB

13. Classification of CIRCUIT BREAKERS:
Circuit Breakers
Oil
Circuit Breakers
Air Blast
Circuit Breakers
SF6
Circuit Breakers
Vaccum
Circuit Breakers
Bulk Oil
Circuit Breakers
Minimum Oil
Circuit Breakers
Plain Break Oil Circuit Breakers
Arc Control Oil Circuit Breakers
Axial Blast Type Circuit Breakers
Cross Blast Type Circuit Breakers
Radial Blast Type Circuit Breakers

14. Minimum Oil Circuit Breaker:-
1. Supporting Chamber
2. Circuit Breaking chamber
3. Top Chamber

16. Advantages:-
1. It requires Less Quantity of oil
2. It requires Smaller Space
3. There is reduced risk of Fire
4. Maintenance Problems are reduced
disadvantages:-
1. Possibility of Fire and Explosion
2. Due to smaller Quantity of oil, the degree of carbonisation is increased
3. There is a difficulty of removing the gases from the contact space in time
4. The dielectric strength of the oil is deteriorates rapidly due to high degree of carbonisation
Applications:-
These are preferred to use for the voltage ranges from 3.3 KV to 66 KV
But the availability range of this minimum oil circuit breakers is from 3.3 KV to 220KV

17. Cross Blast Circuit Breaker:-

18. SF6 Circuit Breaker:- 1. Non puffer type Circuit breaker
2. Single pressure puffer type Circuit Breaker
3. Double pressure Type

19. Double pressure Type Circuit Breaker:-

20. Advantages:-
1. Due to superior arc quenching property of SF6 ,Such circuit breakers have very short arcing time
2. Since the dielectric strength of SF6 gas is 2 to 3 times that of air such breakers can interrupt much larger
currents
3. The SF6 circuit breaker gives noiseless operation due to its closed gas circuit and no exhaust to atmosphere
unlike the air blast circuit breaker
4. Closed gas enclosure keeps the interior dry so that no moisture problem
5. There is no risk of fire because SF6 is non- inflammable
6. There is no carbon deposits
7. SF6 Circuit breakers have low maintenance cost, light foundation and minimum auxiliary equipment.
8. SF6 breakers are totally enclosed and sealed from atmosphere, they are particularly suitable where
explosion hazard exists e.g., coal mines
disadvantages:-
1. SF6 breakers are costly due to the high cost of SF6
2. SF6 gas has to be reconditioned after every operation of the breaker, additionall equipment is
required for this purpose

21. Applications:-
 SF6 Circuit breakers consists of interrupter units each capable of dealing with currents up to 60KA
And Voltages in the range of 50 to 80KV.A number of units are connected in series according to the
system voltage
 SF6 Circuit breakers have been developed for Voltages 132KV to 760KV, Power Ratings 10MVA to
20MVA and interrupting less than 3 cycles
3. It has a property of condensation at low temperature ,i.e., less than 100C SF6 gas liquefies

22. Vacuum Circuit Breaker:-

23. Advantages:-
1. These are compact, reliable and have longer life
2. There are no fire hazards
3. There is no generation of gas during and after operation
4. They can interrupt any fault current. The outstanding feature of a VCB is that it can break any heavy fault
current perfectly
5. They require little maintenance and they are quite in operation
6. They can successfully withstand lightning surges
7. They have low arc energy
8. They have low inertia and hence require smaller power for control mechanism
Applications:-
Vacuum circuit breakers are employed for outdoor applications ranging from 22KV to 66KV
Power rating is 60 to 100MVA they are suitable for a majority of applications in rural areas

24. Minimum Oil Circuit Breaker
Bulk Oil Circuit Breaker

25. SF6 Circuit Breaker

32. Overhauling of CB