When a low power factor penalty appears on a bill, the first assumption is often that the utility meter is wrong. It almost never is. The penalty is a direct measurement of how much reactive power the installation draws, and it is entirely fixable.

Where reactive power comes from

Induction motors, transformers and fluorescent lighting all need a magnetising current to establish their magnetic fields. That current does no useful work, but it still flows through the cables, the transformer and the utility network. The supply company sizes its infrastructure for the total current, so it charges for it.

What correction actually does

An APFC panel connects capacitor banks in parallel with the load. Capacitors draw a leading current that cancels the lagging current of the motors, so the reactive component is supplied locally instead of travelling from the substation. The utility then sees a smaller current for the same real work.

Three effects worth counting

  • The penalty disappears once the measured factor rises above the threshold, typically 0.95.
  • Recorded demand in kVA falls, which reduces the maximum demand charge.
  • Released transformer capacity becomes available for additional load without an upgrade.

Why capacitor banks fail early

Most premature failures come from heat and from harmonics. Capacitors mounted in the same compartment as the contactors run hot, and heat is the primary driver of dielectric ageing. Where variable frequency drives are present, harmonic currents can find a resonant path through the capacitors and overload them.

A well-built APFC panel puts the capacitor bank in its own ventilated compartment, uses contactors rated for capacitive switching duty, and where drives are present, includes detuned reactors. These add cost at purchase and remove the repeat replacement cost that follows a cheap panel.