Classification of circuit breakers

The most important basis for classifying circuit breakers is the medium used for arc extinction, because the medium decides the breaking capacity, voltage range, size, speed and maintenance of the breaker.

Classification by arc quenching medium

1. Air break circuit breaker

   • Arc is drawn in air at atmospheric pressure and lengthened by arc runners, blow-out coils and arc splitters (high resistance method).
   • Application: low and medium voltage up to about 11 kV; LV switchboards, motor control, DC circuits.

2. Oil circuit breaker

   • Arc in oil decomposes it into hydrogen gas which cools and deionises the arc.
   • Bulk oil: oil for quenching and insulation; up to 33 kV (old installations).
   • Minimum oil: oil for quenching only, porcelain for insulation; 3.3–132 kV.
   • Application: outdoor distribution substations (now being replaced).

3. Air blast circuit breaker

   • Compressed air (20–30 bar) blown axially or across the arc.
   • Application: 66–400 kV transmission; where frequent operation and fast auto-reclosing are needed; arc furnaces.

4. SF6 circuit breaker

   • Electronegative SF6 gas blown over the arc (puffer or double-pressure type).
   • Application: 33–765 kV substations, GIS (gas-insulated switchgear).

5. Vacuum circuit breaker

   • Contacts open in a vacuum of 10⁻⁶ to 10⁻⁷ torr; the arc is a metal-vapour arc that vanishes at current zero.
   • Application: 3.3–33 kV indoor switchgear, capacitor and motor switching, railways.

Other bases of classification

• By voltage: low voltage (below 1 kV), medium voltage (1–72.5 kV), high voltage (72.5–245 kV) and extra high voltage (above 245 kV).
• By location: indoor and outdoor breakers.
• By operating mechanism: spring, pneumatic, hydraulic, solenoid.
• By external design: dead tank (enclosure at earth potential) and live tank (interrupter at line potential).
• By interrupting principle: high resistance interruption (DC and LV) and low resistance or current-zero interruption (AC HV).

Summary table