THE EFFECT OF DC OFFSET ON INSTANTANEOUS OPERATING CHARACTERISTICS OFLOW-VOLTAGE CIRCUIT-BREAKERS

This paper addresses the effect of asymmetrical currents on factory ad justments and field verification of low-voltage circuit breaker instan taneous trip units. Both molded case circuit breakers (MCCB's) and pow er circuit breakers are pertinent, Factory adjustment of low-voltage c ircuit breakers, based on test results using asymmetrical current, may cause the circuit breaker instantaneous unit to perform improperly an d result in inadequate protection and coordination of electrical syste m apparatus, Similarly, field testing conducted to verify proper perfo rmance of low-voltage circuit breakers, using asymmetrical current, ma y lead to the erroneous conclusion that the circuit breaker's instanta neous unit is out of specification. In addition to addressing the diff iculties presented by this phenomenon, this paper also proposes an app roach to identifying and overcoming these testing difficulties.