JPS6484158A - Electric power detector - Google Patents

Abstract

PURPOSE:To accurately detect the input electric power of a three-phase load at a high speed by multiplying a mean phase voltage by a mean effective current, and calculating and outputting mean electric. CONSTITUTION:When a three-phase current is supplied to the three-phase load, a voltage transformer 3 obtains respective phase voltage signals VR, VS, and VT and a current transformer 4 obtains respective phase current signals V1R, V1S, and V1T. A comparator 7 outputs polarity detection signals (a), (b), and (c) corresponding to the respective phases. Then a mean effective current arithmetic circuit 8 computers a mean effective current signal IA by integrating the respective phase current signals V1R, V1S, and V1T with the polarity detection signals (a), (b), and (c) for periods of half cycles synchronized with phase voltage signals VR, VS, and VT, Then a mean phase voltage arithmetic circuit 9 computes a three-phase voltage signal VA by adding the phase voltage signals VR, VS, and VT with the polarity detection signals (a), (b), and (c) for the periods of the half cycles. Then an electric power arithmetic circuit 10 calculates the product of the mean phase voltage signal VA and mean effective current signal IA and outputs an electric power detection signal VP. Consequently, the three- phase mean electric power can be detected.