MISINTERPRETATIONS OF SOME POWER PROPERTIES OF ELECTRIC-CIRCUITS

It might be expected that the meaning of the apparent power S, a quantity of innumerable everyday applications for almost a century, is well understood. It occurs, however, that this meaning is still a matter of discussions and some interpretations hard to accept are published. Also it is suggested in some papers published recently that only oscillations of the instantaneous power may cause an increase of the apparent power S, which is not true. Misinterpretations that refer to fundamental notions such as powers could be particularly harmful for electrical engineering and should be eliminated as much as possible. Therefore, this paper shows that the apparent power does not have the physical meaning suggested recently. Also it shows that loads unbalance in three-phase systems does not cause any oscillation of the instantaneous power. The conclusion that loads unbalance causes oscillations of the instantaneous power is a consequence of a substantial misinterpretation of this quantity in three-phase systems.