Differential element with harmonic blocking and harmonic restraint operating in parallel

摘要

An intelligent electronic device (IED) provides harmonic blocking and harmonic restraint differential protection operating in parallel. The IED includes a harmonically-blocked differential element supervised by one or more even harmonics of a raw operating current (a current comprising the fundamental operating current and the harmonics thereof). The IED also includes a parallel, harmonically-restrained differential element, which is restrained by harmonics of the raw operating current. Tripping signals output by the parallel harmonically-blocked differential element and the harmonically-restrained differential element may be selectively combined into a single tripping signal output. An additional harmonic blocking element may supervise both differential elements and/or the combined tripping signal. The additional harmonic blocking element may provide odd-harmonic blocking, such as harmonic blocking based on a fifth harmonic of the raw operating current.