Apparent power and power factor concepts in unbalanced and nonsinusoidal situations

This contribution discusses the concept of apparent power and the related concept of power factor in general, sinusoidal and nonsinusoidal, polyphase, balanced and unbalanced situations. In the classical case of single-phase sinusoidal voltage and current the apparent power and the power factor are defined by a quantitative (mathematical) expression, for the generalization a physical interpretation is necessary. In this contribution, the apparent power is associated with the maximal ´useful´ power that can be delivered under ´given circumstances´. It is shown that the terms ´useful power´ and ´given circumstances´ should be carefully defined. Depending on the way they are defined, different results are obtained. For unbalanced and nonsinusoidal conditions various definitions of useful power are considered; particular attention is given to the case where the positive sequence and/or fundamental frequency power is considered to be the useful power.