Speaker: Daniel Carreno Perez, Megger
Selective coordination of a power system can be a large investment to ensure that the system is protected and power is maintained properly. Part of the commissioning standards and maintenance procedures of low voltage circuit breaker testing is to determine if the circuit breaker is able to respond correctly to the faults or overloading conditions set in the coordination study.
When this coordination study includes ground fault as a part of the low voltage circuit breaker protection scheme, the best approach to test these elements is with primary injection. There are various techniques for detecting a ground fault in low voltage circuit breakers such as Residual Earth-Fault, Zero Sequence, Neutral Protection, and Earth Leakage. Testing with primary injection ensures that the applicable current transformers (CT’s), main contacts, wiring, and trip unit are tested together as one complete circuit.
This presentation will cover the challenges of ground fault testing of low voltage molded case and power circuit breakers using primary injection such as cable length, power sources, breaker configurations, CT polarity, CT sizing, and why primary injection is specified per NEC standards and NETA.