An electrical power system is very complex. In power system, circuit breakers are usually employed for the protection of electrical circuits. A circuit breaker is a mechanical switching device that is used for closing or opening of an electrical circuit under normal or abnormal conditions.

A circuit breaker has fixed and moving contacts. These contacts are called electrodes. Under normal working conditions, these contacts remain in contact and will not open automatically until and unless the system becomes faulty. Whenever a fault occurs the trip coil of the breaker coils of the breaker gets energized and moving contact pulled apart by some mechanism, thus opening the circuit.

During the separation of breaker contacts, an arc is struck between them. The current is thus able to continue until the discharge ceases. This production of arc delays the current interruption process and at the same times it generates enormous heat which may cause damage to the system or to the circuit breaker itself. Thus the main problem is to extinguish the arc whenever it occurs in circuit breaker.

Circuit Breaker
Basic View of Circuit Breaker

Arc Phenomenon

When a fault occurs, a heavy current flows through the contacts of the breaker. When the circuit begin to separate, the contact area decreases rapidly and large current flows through air (medium) hence rise the temperature. This heat is sufficient to ionize the air (medium). The ionized air acts as a conductor having low resistance and arc is struck between the contacts.   The arc provides low resistance path to the flow of electric current. This current remains uninterrupted as long as the arc persists

Classification of Circuit Breakers

There are several ways of classifying the circuit breakers. But, more generally the circuit breaker is classified on the basis of medium used for arc extinction. The medium used for arc extinction is usually oil, air, vacuum or sulphur hexafluoride.

  • Oil Circuit Breakers
  • Air Circuit Breakers
  • Sulphur hexafluoride Circuit Breaker
  • Vacuum Circuit Breakers