By Nils Wacklen – product manager, circuit breaker testing, Megger Sweden
After long periods of inactivity, a circuit breaker must function perfectly when needed. The best opportunity to test for this is the first-trip test. The rated operating sequence (also known as the standard operating duty or standard duty cycle) is the specified operating sequence that the circuit breaker must be able to perform at specified ratings. Breaker manufacturers normally specify these sequences and corresponding rated times, which are defined in IEC 62271-100.
Many regulations and laws require all electrical equipment to be grounded on both sides before any maintenance work is carried out. During circuit breaker maintenance, however, the most basic and important test – main contact timing – is usually performed without this basic safety prerequisite. The reason is simple; conventional technology does not offer a safe way of carrying out timing tests on circuit breakers. Now, however, DualGround/DCM technology offers a much safer approach to testing.
First introduced in 2006, this novel testing technique offers greatly increased safety for personnel, and is suitable for use with circuit breakers of all types. It is non-intrusive and does not require any special preparatory information. Despite these benefits, the basic method of working and the interpretation of results remain unchanged, except that testing is much faster and easier.