Test of Circuit Breakers Under Harmonic Loading Conditions

摘要

Harmonic currents in Army installation power systems can cause voltagedistortion, overheating of system components, and load disruption. The U.S. Army Center for Public Works also has periodically received reports of unexplained nuisance circuit breaker tripping, which in theory might be caused by harmonics. No industry standard literature is available on the behavior of circuit breakers under harmonic loading conditions, however. The objective of this work was to test the effects of harmonic loading conditions on three common types of low voltage, molded case circuit breakers used indoors on Army installations: thermal magnetic, magnetic only, and solid state. This experiment detected no nuisance tripping with any of the breakers tested. Additionally it was found that varying harmonic loading conditions did not affect manufacturer specified trip times for thermal magnetic or solid state circuit breakers. However, under moderate overload conditions, the same experimental harmonic conditions caused hazardous overheating and trip failure in the magnetic only circuit breakers. Based on a review of related nonexperimental industry literature on circuit breaker design and performance, the authors postulate that inherent design characteristics leave thermal magnetic and solid state circuit breakers unaffected by harmonics. The literature also suggests that the construction of the instantaneous tripping element in the magnetic only breakers may account for their overheating and trip failure in the experiment.