THREE-PHASE WATTMETER

• Main Author: SHIODA TOSHIAKI
• Format: Patent
• Language: English
• Published: 14.12.1999
• Edition: 6
• Subjects: MEASURING; MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES; PHYSICS; TESTING

PROBLEM TO BE SOLVED: To accurately measure three-phase active power, reactive power and apparent power even when there are unbalance of a three-wire load and waveform distortion by measuring a phase current of first/third phases of a three-phase alternating current, measuring interphase voltage of first/second phases and second/third phases, and separately performing an operation on the real number part and the imaginary number part of interphase voltage and an interphase current from a result of a Fourier analysis. SOLUTION: In a phase current A1 of a first phase, a prescribed signal is obtained in an output terminal 27 of an FFT processor 22 by performing a Fourier analysis, and in interphase voltage V1 of first/second phases, a signal is obtained in a terminal 17. A complex multiplier 13 performs multiplying processing on the signals of the terminals 27, 17 by a prescribed expression to output interphase active power W1 of the first/second phases to a real number part output terminal 15, interphase reactive power var1 to an imaginary number part output terminal 25 and similarly active power W3 and reactive power var3 to terminals 35, 45. An adder 14 obtains three-phase active power ΣW in an output terminal 16 by performing adding processing on the powers W1, W3, and an adder 34 similarly obtains Σvar. A square sum extractor 50 obtains ΣVA of three-phase apparent power by the active power and the reactive power Σvar to thus determine active/reactive apparent powers without an error.