Circuit Breaker Contacts The circuit breaker contacts are required to carry normal as well as short-circuit current. In carrying the normal current, it is desirable that the temperature should not rise above the specified limits and that there should be low voltage drop at the point of contact....
The circuit breaker contacts are required to carry normal as well as short-circuit current. In carrying the normal current, it is desirable that the temperature should not rise above the specified limits and that there should be low voltage drop at the point of contact.
In carrying breaking and making short-circuit currents, the chief effects to be dealt with are melting and vapourisation by the heat of the arc and those due to electromagnetic forces. Therefore, the design of contacts is of considerable importance for satisfactory operation of the circuit breakers.
There are three types of circuit breaker contacts viz.
Tulip type contacts
Finger and wedge contacts
Butt contacts
It consists of moving contact which moves inside the fixed contacts. At contact separation, the arc is generally established between the tips of the fixed contacts and the tip of the moving contact. The advantage of this type of contact is that arcing is confined to the regions which are not in contact in the fully engaged position.
This type of contact is largely used for low-voltage oil circuit breakers owing to the general unsuitability for use with arc control devices.
The butt type contact and is formed by the springs. It possesses two advantages.
Firstly, spring pressure is available to assist contact separation. This is useful in single-break oil circuit breakers and air-blast circuit breakers where relatively small “loop” forces are available to assist in opening.
Secondly, there is no grip force so that this type of contact is especially suitable for higher short circuit rating.
