Methods of Circuit Breaker Arc Interruption

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.

Further Reading