One of the most critical devices on any electricity network is the circuit breaker which can be described as the silent sentinel, standing guard over the network and only being called into action when a fault occurs.
The circuit breaker needs to operate within its composite tripping time (relay trip time plus circuit breaker main contact opening time) to ensure correct discrimination with upstream circuit breakers and, therefore, minimize the number of customers disconnected during a fault operation. A slow tripping circuit breaker will not only result in unnecessary disruptions to electricity supplies, but maintaining high fault currents for extended durations can stress the network and cause damage to plant and equipment. Often the problem that caused a slow trip is temporarily cleared during the first trip operation because friction in the mechanism is reduced by spreading lubrication during the motion of tripping. Traditional diagnostic testing procedures usually require the circuit breaker to be isolated and removed from service; therefore, not only has the opportunity to detect the cause of the defect been missed but also the tests do not focus on the condition of the operating mechanism apart from overall speed of operation.