Power Factor from Real and Apparent Power

Power factor is an efficiency of delivery, not of conversion: it says how much of the capacity you rented from the utility is producing work. A load reading 8 kW on the wattmeter but 10 kVA on the volt-amp meter runs at PF = 0.8, meaning a fifth of the supplied capacity is sloshing back and forth building magnetic fields instead of turning shafts. Both fields here are watt fields; enter kVA in the kW box, since VA and W are the same dimension.

Utilities care because that reactive current still heats their conductors and transformers, so large customers face a power-factor penalty — often triggered below 0.9 or 0.95. Lightly loaded induction motors are the usual culprit, drifting to 0.3–0.5 PF at no load; the standard cures are capacitor banks and, better, not oversizing motors in the first place.