All circuit breakers have contacts, and when the contacts separate during a fault clearing operation, they draw an arc. The electric arc forms between the contacts and is drawn out in length as the contacts open.
For this reason, circuit breakers require a device to control or remove the arc. The four common mediums used to extinguish an arc during breaker contact separation are Oil, Air, Gas, and opening in a Vacuum.
Air-break circuit breaker
- Used for low voltages, generally up to 15KV and rupturing capacities of 500MVA.
- Contact separation and arc extinction take place in air at atmospheric pressure.
- Arc is expanded by the mean of arc runners, arc chutes, and arc resistance is increased by splitting, cooling and lengthening.
- Widely employed indoor medium voltage and low voltage switchgear.
- Inefficiency at low currents where the electromagnetic fields are weak.
Air-blast circuit breaker
- Used compressed air or gas as the arc interrupting medium.
- Compressed air is stored in a tank and released through a nozzle to produce a high-velocity jet.
- Generally used for voltages of 15kV and rupturing capacities of 2500 MVA.
- Final gap required for arc extinction is very small.
- Extinguishes the arc within one or more cycles.
- Compressed air at the correct pressure must be available all the times.
SF6 circuit breaker
- Uses sulferhexafloride to extinguish arc up to 800 kV.
- Arc quenching capabilities is almost 100 times better than air.
- Dielectric strength of SF6 increases with pressure.
- Smaller breakers can be used at higher voltages.
- Require less maintenance than air blast or oil breakers.
- Nitrogen and freon-14 are added to keep SF6 gasified at lower temperatures.
- Dead tank breakers have grounded tanks. Live tank breakers are energized at system voltage.
Vacuum circuit breaker
- Arc quenching takes place in vacuum chamber (vacuum interrupter).
- Suitable for mainly medium voltage application.
- Technology was first introduced in the year 1960.
- Requires minimum maintenance compared to other circuit breaker types.
- Environment friendly, reduced fire hazard.
- Simple to retrofit existing air breakers.
- Dielectric strength is eight times greater than that of air and four times greater than that of SF6 gas.
Tank type oil circuit breaker
- Uses oil as a dielectric or insulating medium for arc extinction.
- Heat of the arc is evaporated in the surrounding oil.
- Consists of current carrying contacts enclosed in a strong, weather-tight earth metal tank filled with oil.
- The oil has a high dielectric strength and provides insulation between the contact after the arc has been extinguished.
- Typically located outdoors.
- Used in high voltage applications and distribution systems for up to 220 kV.
