Frequency characteristics and switching, operating characteristics of Circuit breaker

Rated frequency of circuit breaker

Two frequencies are currently used throughout the world: 50 Hz in Europe and 60 Hz in America, a few countries use both frequencies. The rated frequency is either 50 Hz or 60 Hz.

The performance of a circuit breaker is same for both the frequencies 50HZ and 60HZ ac network. Same thermal effect and other performance for up to 60HZ of a circuit breaker. Special consideration is required for frequency above 60HZ.

Switching sequence & Operating sequence of circuit breaker

We should not switch on or off a circuit breaker or operate a circuit arbitrarily; there is some specific standard for switching and operating sequence of a circuit breaker.

Switching sequence

Rated switching sequence of circuit breaker according to IEC(International Electro technical Commission), O – t – CO – t’ – CO. (cf: opposite diagram)

O : represents opening operation

CO : represents closing operation followed immediately by an opening operation

t = time

So after opening the circuit breaker there should be some time gap, then closing operation. The the next time gap should be a little more. This is explained below.

Operating sequence

Three rated operating sequences exist:

v slow: 0 – 3 minute – CO – 3 minute – CO

v quick 1: O – 0.3 s – CO – 3 minute – CO

v quick 2: O – 0.3 s – CO – 15 s – CO

                                            Fig: Rated operating sequence of circuit breaker