The most carefully set protection is pointless unless the circuit breaker operating times are established.
Even the most carefully planned discrimination can fail due to the poor operation of circuit breakers. Our experience shows that many older circuit breakers far exceed their stated opening times. To confirm the opening and closing times of electrically operated circuit breakers Addelec Power Services use the Digi TMR S2 Circuit Breaker Analyser.
The Digi TMR S2 can be operated stand-alone or can be computer controlled. It can fully analyse a circuit breaker’s performance by testing contact time, stroke, velocity and over travel. It measures elapsed time from the instant a breaker coil is powered to the instant of opening or closing of the circuit-breaker’s dry contacts. A built-in hall-effect current sensor records the circuit breaker’s operating coil current amplitude and duration (effectively, a performance “finger print” or current profile). A voltage monitoring input is dedicated to monitoring the substation DC supply or coil voltage (giving a good indication of the station battery system under load).
The Digi-TMR S2 not only times the breaker’s contact response time, but it can also time relays or other switching functions that use an initiating-trigger voltage.
The measurement of the main contact resistance of circuit breakers gives reliable information on the condition of devices particularly after clearing a major fault .The measurement of contact resistance at commissioning stage for fingerprinting purposes gives valuable information for monitoring the device during service. To carry out these measurements we use highly accurate micro-ohm meters.
Prevention is always better than cure – and generally more cost effective!