Power factor (cos φ)
The voltage/current phase shift, the link between apparent and active power.
Definition
The power factor, often equated with cos φ, expresses the ratio between active power (in watts, genuinely useful) and apparent power (in VA, genuinely drawn). It reflects the phase shift between voltage and current introduced by inductive or capacitive loads.
A power factor close to 1 means almost all the power drawn is converted into useful work. A low cos φ (highly inductive loads: motors, ballasts) forces the transformer and the network to supply a higher current for the same useful power, increasing losses and heating.
This is why a transformer is sized in apparent power: it must handle this current, whatever the load’s power factor.
The ABL tip
If your loads are strongly inductive, state their cos φ: we take it into account for sizing, and can point you to compensation solutions to reduce the current drawn and your losses.
