SOLUTION

Rated Voltage of circuit breaker:- During normal operating conditions the voltage at any point of the power system is not constant. Due to this, the manufacturer guarantees perfect operation of the circuit breaker at the rated maximum voltage, which as a rule is higher than the rated nominal voltage. The rated voltage of the circuit breaker depends upon its insulation system. For below 400 kV systems, the circuit breaker is designed to withstand 10% above the normal system voltage. For an above or equal 400 kV system the insulation of the circuit breaker should be capable of withstanding 5% above the normal system voltage

The rated maximum voltage of a circuit breaker is the highest RMS voltage, above nominal system voltage, for which the circuit breaker is designed and is the upper limit for operation.

or

The rated maximum voltage of the circuit breaker is the highest RMS phase-to-phase voltage for which the circuit breaker is designed, and is the upper limit for operation.