Phase loss detection circuit including transient protection

Abstract

A phase loss detection circuit for a three phase electrical system providing three phase power as to a motor, the three phase electrical being subject to a phase loss condition and a transient condition is disclosed. The transient condition includes starting transients, stopping transients or severe load transients. The phase loss detection circuit distinguishes between a phase loss condition and a transient condition and indicates when a loss of phase has occurred. The phase loss detection circuit comprises a detector for detecting an instantaneous voltage of the electrical system, a sensor for generating an instantaneous voltage signal representing the instantaneous detected voltage, a detector for detecting a peak detected voltage of the electrical system, a generator for generating a peak detected voltage signal representing said peak detected voltage, a comparator for comparing the peak detected voltage with the instantaneous voltage and generating a compared signal, the compared signal comprising a first polarity during steady state operation, a second, opposite polarity during the transient condition and an alternating polarity during the phase loss condition, and a detector for detecting the alternating polarity, thereby indicating the phase loss condition.