COVER FEATURE Circuit Breaker Testing Complexities Removed By Aditya Taneja and Ulrich Klapper, Omicron Electronics A circuit breaker is an electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. It is also used to isolate part of a healthy circuit for regular maintenance. Its operation can therefore be both automatic and manual. Its basic function is to immediately discontinue electrical flow. The circuit breaker plays a significant role within the power system where it: • Minimises losses in closed position. • Opens and closes on command. • Opens or closes a circuit to connect the power to/from the transmission line (O - break, C - make). • Opens a circuit for planned maintenance (O - break). • Opens a circuit at system fault to protect the system behind the circuit breaker (O - break, O-C -reclose, O-CO auto- reclose). • Isolates between poles (TRV), open contacts and earth. To ensure appropriate operation of the circuit breaker it is important to test the performance of key components including: • kinematic chain (timing of main and auxiliary contacts and contact travel (motion) of main contacts), • control circuits (coil current analysis, minimum pick-up test), • charging motor (motor current analysis), • main contacts’ wear and tear (contact resistance of main contacts – static and dynamic). Conventional testing of circuit breakers generally means the disconnection of the circuit breaker from the system. It is imperative that testing is done in the shortest possible time, utilising equipment which provides accurate results. The conventional set-up for circuit breaker testing involves rewiring between 14 micro-ohm measurement and timing tests. This involves many cables, is time- consuming and error-prone. The wiring for the micro-ohm certainly is not done all in parallel in the conventional set-up; however all the wires shown in the picture are needed. Conventional wiring set-up for micro-ohm measurement Conventional wiring set-up for timing tests Classic circuit breaker testing Traditionally, reference to circuit breaker testing excluded the static resistance measurement, despite the fact that this is an absolutely necessary test. OMICRON defines circuit breaker testing as: • the distribution of open and close commands of the circuit breaker with nominal and under voltage; • analysis of coil currents; • the measurement on the main and auxiliary contacts; • static contact resistance test; and if necessary • a dynamic resistance measurement of the main contacts; • motion analysis or time travel diagram. Testing system plan OMICRON’s new CIBANO 500 test system combines, in a single device, the three devices which are typically required for circuit breaker testing, including: • Circuit breaker testing. • Micro-ohm measurement. • Breaker supply. The measurements possible with this combination of equipment enable the user to draw numerous conclusions regarding the condition of the circuit breaker. Through the analysis of coil circuits from the different open and closed coils, it can be determined whether an operating characteristic of any nature or manner is sluggish, and compare the chronological sequence with nominal values. Timing analysis gives information on whether the different main and auxiliary contacts are switching within the correct time, according to the manufacturer’s specified nominal behaviours. Synchronisation of individual main contacts within a phase is therefore particularly important, but also between the phases of the maximal permissible deviations indicated by the manufacturer. The dynamic resistance measurement allows the recording of resistance during the opening of the main contacts. The point in time the current line passed from the main to the arcing contact can be read from the curve. CIBANO 500’s three-in-one solution. ESI AFRICA ISSUE 1 2014