A comparison among apparent power definitions

This paper presents a survey of modern apparent power definitions. At this time there are two dominant schools of thought; The European group that uses a purely theoretical approach based on the fundamental laws of circuit theory and the North American group that advocates a more pragmatic definition stemming from the fundamental concepts underlining the utilization of three-phase lines. Differences among the presented methods stem from the way in which the line resistances are accounted for and how the loads are compensated to reach unity power factor. It was found that the discussed methods give very close results. For practical situations the differences are of the same order of magnitude as the error of metering instrumentation.