A circuit breakers is an mechanically operated switch designed to shield an circuit from harm caused by excess current from associate degree overload or short circuit( a fuse is reset (either manually or automatically) to resume traditional operation). Circuit breakers are rated each by the traditional current that they’re expected to hold, and also the most short-circuit current that they will safely interrupt.
In substations, the wattage transmission networks are protected and controlled by High Voltage fuse within electrical grid station. In substations the protection relay theme may be complicated, protective instrumentality and busses from varied kinds of overload or ground/earth fault. Electrical protection ought to be provided against the subsequent abnormal conditions:
overloading (excessive currents not due to faults)
short-circuit faults between phases
short-circuit faults to earth
According to their arc quenching (rapid cooling) media the circuit breaker can be divided as:
• 1) Air circuit breaker
• 2) Oil circuit breaker
• 3) Vacuum circuit breaker
• 4) SF6 circuit breaker
According to their services the circuit breaker can be divided as:
• 1) Outdoor circuit breaker
• 2) Indoor circuit breaker
According to the operating mechanism of circuit breaker they can be divided as:
• 1) Spring operated circuit breaker
• 2) Pneumatic circuit breaker
• 3) Hydraulic circuit breaker
According to the voltage level of installation types of circuit breaker are referred as:
• 1) High voltage circuit breaker (> 72 kV)
• 2) Medium voltage circuit breaker (1-72 kV)
• 3) Low voltage circuit breaker (< 1 kV)
A vacuum circuit breaker could be a reasonably breaker wherever the arc termination takes place in vacuum medium. The operation of switch on and shutting of current carrying contacts and reticulated arc interruption takes place in a very chamber within the breaker that is termed vacuum device.
Vacuum circuit breaker (VCB)
SF6 Circuit Breaker
Sulfur hexafluoride (SF6) gas is another to air as associate degree interrupting medium. SF6 could be a colorless nontoxic gas, with sensible thermal conduction and density just about 5 times that of air.
The principle of operation is analogous to the air blast breakers, except that the SF6 gas isn’t discharged into the atmosphere.
A closed circuit completely sealed and self-contained construction is used. SF6 Circuit Breakers are mostly use in Indoor type Primary sub stations.SF6 Gas has good qualities as below.
1. Good heat transfer quantity.
2. Pressure can be checked easily
3. Short arcing time
4. Compartmented SF6 HV load-break isolating switch