APFC Panel
An APFC panel automates power factor correction: a relay measures live power factor and switches capacitor steps in or out so correction always matches the load — avoiding both under-correction penalties and leading-PF over-correction.
Why it matters on an MEPF project
Fixed capacitors correct one load point; factories don't have one load point. The APFC's stepped banks and controller ride the load curve — heavy shifts, light nights, weekend idling — holding PF in the incentive band throughout. Step sizing matters: too-coarse steps hunt or overshoot; a sensible ladder (mixed step sizes) settles smoothly.
It is also a real panel with real failure modes: capacitor cans age (capacitance drift, bulging), contactors for capacitor duty wear fast, and in harmonic-rich plants the steps must be detuned reactors + capacitors, not bare cans. An APFC that silently lost half its steps is the classic "penalty is back" story — annual step-by-step verification belongs in the AMC.
How it's specified in practice
| Parameter | Typical / working position | Governing reference |
|---|---|---|
| Controller | PF relay switching steps to target setpoint | panel design |
| Steps | Mixed kVAr ladder for fine control | design practice |
| Switching | Capacitor-duty contactors (or thyristor for fast loads) | component selection |
| Harmonics | Detuned reactors standard in drive-heavy plants | power-quality practice |
Common mistakes
- One giant step "for simplicity" — the controller can only overshoot.
- Ordinary contactors switching capacitors — short, sparky lives.
- No periodic capacitance measurement; dead cans hide until the bill tells.
- Ignoring ventilation — capacitors and reactors run warm and hate hot panels.
Related on this site
One of 68 working definitions in the MEPF & solar engineering glossary. The buying side of the same decisions is in the buyer's guides; the numbers are in the calculators.
Frequently asked
APFC vs fixed capacitors — when is automatic worth it?
Whenever load varies meaningfully across shifts/days — which is nearly every factory. Fixed banks fit steady base loads (e.g., permanently-on transformer compensation) as a complement, not a substitute.
Why does my APFC show leading PF at night?
Steps too coarse for the light load, or the controller setpoint/step logic mis-set. Leading PF can attract penalties too — night-shift PF deserves the same attention as peak.
Standards referenced: IEC 61439 (assembly) · state tariff orders (PF bands)