# Circuit breakers usually operate under

Circuit breakers usually operate under

### Right Answer is: Transient state of short-circuit current

#### SOLUTION

Fault current is divided into phases: Subtransient, Transient, and Steady State.

The Subtransient phase is defined as the level of fault current during the first few cycles of the fault current. The fault current is at its most severe level during this time period, and the DC decay is at its most rapid rate. So, while it is a severe level, it doesn’t last very long.

The Transient phase is that period after the subtransient period and lasts until the current level decays to normal current levels. It is less severe but lasts longer than the subtransient phase. The circuit breaker operates at the transient phase.

The Steady-State phase is the normal current level—the fault current has decayed fully.

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