Vacuum Circuit Breaker

A vacuum circuit breaker is an electrical switch which makes or breaks an electrical circuit during a short circuit fault or overload condition. It comes under the protection of the power system where large amount of fault current hampers the system. In case a fault occurs in any electrical system, the relay senses the fault and sends the message to the circuit breaker which disconnects the circuit from the fault circuit thus protecting the electrical equipments. A circuit breaker can resume its normal operation after the fault has been cleared. A circuit breaker is an important protection device used for the timely disconnection and reconnection of the electrical circuit after the clearance of the large magnitude fault current.

Based on the arc quenching media, circuit breakers are divided into 4 types:

·         Gas filled type

·         Oil filled type

·         Vacuum type

·         SF₆  type

We are here to discuss about the vacuum circuit breaker.

Operating principle:

 It is a type of circuit breaker in which the arc quenching is done in the vacuum medium of the breaker. This type of breakers is generally used in medium voltage power transmission. The basic principle of operation of such a breaker is the vacuum interrupter which consists of ceramic insulators surrounded by steel arc chambers on either side. The performance of this breaker depends hugely on the type of material used for the current carrying contacts. Any circuit breaker aims to quench the arc with minimum power loss. As the dielectric strength of vacuum is much more than that of air or SF₆ it is far more advantageous than any other type of circuit breaker. It quenches the arc with its high dielectric strength with a very small contact gap.

Whenever the arc is initiated, the de-touching of the contact creates a hot spot in the gap between the contacts. Being vacuum the metals touching the contact vaporises due to the presence of the hot spot and it creates a conducting medium for the arc to flow. Once the arc is completely extinguished, the conducting metal plate re-condenses and by that time the contacts are already disconnected from each other. This prevents the reestablishment of the arc and hence reduces arc quenching by this process.

Uses of vacuum circuit breaker:

Vacuum circuit breakers have a wide range of application for the industrial and commercial medium voltage transmission in a power system.

-          Vacuum contactor for switching of motors

-          Use in transformer

-          Applicable in motor circuits

-          In substations and switchyards