SHORT CIRCUIT TESTING OF CIRCUIT BREAKERS.

This paper concentrates on switchgear as a protective device and as a switching device and is mainly confined to circuit-breakers. In practice a switching operation is one carried out under controlled conditions to a pre-arranged procedure in order to switch on a load, or switch off a lead, or to switch a load from one circuit to another. The load may be mainly resistive but could be highly capacitive in the case of a capacitor bank, cable or overhead line, or highly inductive in the case of a reactor, a stalled motor or an unloaded transformer. As a protective device the circuit-breaker would be operated by signals from protection equipment under abnormal fault conditions. There are a variety of tests which have to be performed to cover both switching conditions and fault conditions. These fault conditions are generally referred to as short-circuits.