Modern apparent power definitions: theoretical versus practical Approach-the general case

The definition of apparent power for unbalanced or non-sinusoidal three-phase systems is still a controversial issue. Two schools of thought are prevalent at this moment. Both schools define the apparent power as the maximum active power that can be delivered to the load while adjusting or maintaining unchanged certain equivalent values of load voltages and currents unchanged. However, one definition uses a pure mathematical approach that leads to a condition where negative and zero-sequence currents may be present. The second definition is based on a practical engineering concept based on assumption that unity power factor implies a perfectly balanced system with pure positive-sequence voltages and currents, (neutral current nil). This paper starts with the theoretical analysis of the most general case when both the network and the load are unbalanced. Comparison among the results obtained by using the two methods indicate minor differences, nevertheless the unity power factor requirement for symmetrical and balanced condition seems to be the better approach for the apparent power definition.