When there is a problem with the system to which it is connected, the circuit breaker is required to perform the principal functions. Under fault conditions, a circuit breaker is required to perform the following duties:
- Breaking the fault current and opening the defective circuit.
- Being too close-minded to a fault.
- While another circuit breaker (in series) is clearing the fault, temporarily carrying fault current.
All are discussed in the following part in details.
Breaking capacity:
It is quantity of current(RMS) that a circuit breaker is capable of breaking at a given recovery voltage and under specified conditions(power factor, rate of rise of re-striking voltage).
The fault current's r.m.s value at the moment of contacts separating is always used to express the breaking capacity.
When the fault occurs, due to the presence of a DC component, there is a significant Asymmetry in the fault current.
Making capacity:
Making capacity is the maximum value of current (including the d.c. component) during the first current wave cycle following the closing of the circuit breaker.
Short-time rating:
It refers to the period of time that the circuit breaker can carry fault current while still being closed.
Sometimes a fault on the system is very temporary nature and persist for 1 or 2 seconds, after which the fault is automatically cleared.
To keep the power supply continuous in this situation, the breaker shouldn't trip. Therefore, a circuit breaker must be capable of carrying large current safely for a set amount of time.
If the fault persists for longer duration than the specified time limit, the circuit breaker will be tripped for disconnecting the faulty section.
.png)
.png)
0 Comments