Power Factor Correction

Quick pick (TL;DR)

Size the capacitor bank from Qc = P·(tan φ₁ − tan φ₂), where φ₁ is the existing and φ₂ the target power factor (usually 0.95).
Use automatic stepped (APFC) banks for varying load, fixed for steady.
Where the load is harmonic-rich (VFDs), use detuned (7%) reactors or an active filter — plain capacitors resonate and fail.
Correcting 0.75 → 0.95 typically cuts the kVA by ~20%.

Step 1 — Why correct

Benefit	Effect
Lower kVA	More capacity
Lower current	Less loss
Avoid penalty	Save cost

Step 2 — Worked sizing

500 kW, PF 0.75 → 0.95

Capacitor formula Qc = P · (tan φ₁ − tan φ₂) Given P = 500 kW PF₁ = 0.75 → tan φ₁ = 0.882 PF₂ = 0.95 → tan φ₂ = 0.329 Step 1 — Capacitor kVAr Qc = 500 × (0.882 − 0.329) Qc = 500 × 0.553 = 277 kVAr Step 2 — kVA reduction S₁ = 500/0.75 = 667 kVA S₂ = 500/0.95 = 526 kVA saved = 141 kVA (~21%) Answer → ~275 kVAr detuned APFC bank

Capacitor supplies the reactive difference; 0.75→0.95 frees 141 kVA. Don't over-correct past unity.

Step 3 — Bank type

Fixed for steady; APFC for varying load.
Detuned/active for harmonic loads.
Locate at load / MCC / incomer.

Capacitor sizing calculator

Capacitor kVAr & kVA reduction

Qc = P·(tan φ₁ − tan φ₂).

Power P (kW)

Existing PF

Target PF

Don't over-correct past unity; use detuned reactors on harmonic loads.

Common mistakes

Plain capacitors with harmonics.
Over-correcting to leading PF.
Fixed bank on variable load.

Requisition & datasheet

Power, PF, voltage, harmonics.
kVAr, type, detuning, steps.

Frequently asked questions

What should I know about Power Factor Correction?

Size the capacitor bank from Qc = P·(tan φ₁ − tan φ₂), where φ₁ is the existing and φ₂ the target power factor (usually 0.95). Use automatic stepped (APFC) banks for varying load, fixed for steady. Where the load is harmonic-rich (VFDs), use detuned (7%) reactors or an active filter — plain capacitors resonate and fail. Correcting 0.75 → 0.95 typically cuts the kVA by ~20%.

Which standards or codes apply?

IEC 61921 (LV PFC banks), IEC 60831 (capacitors), IEEE 18/1036, IEEE 519 (harmonics limits).

Standards — IEC 61921; IEC 60831; IEEE 18/1036; IEEE 519.