True power factor metering for m-wire systems with distortion, unbalance and direct current components

Abstract

Two companion papers describe an internally consistent general power theory valid for instantaneous and average power for systems with any number of wires, under conditions of unbalance, distortion or dc components. Measuring apparent power and power factor under non-ideal conditions, even in typical three-phase four wire systems, needs the resistances of the wires, particularly the neutral wire, to be defined, and without this detail all conventional power theory approaches are inadequate and give misleading measurement results. This paper illustrates the practicality of measurement of distorted power supplies, and describes laboratory tests showing the differences between measurements using the new approach and a conventional instrument. Applications of the new approach in real power systems are described, including hybrid ac/dc systems and smart grids, and in measuring quality of supply affected by disturbing loads, and the non-active power in transformers subjected to geomagnetically induced currents. The nature of changes required in international standards and the implications for further practical research and development are identified.