Intermediate
Capacitor kVAR Sizing Formula
Size power factor correction capacitors — calculate required kVAR from existing and target power factor.
Formulas
kVAR = kW × (tan φ₁ − tan φ₂)
Required capacitor kVAR
φ = arccos(PF)
Phase angle from power factor
Variable Definitions
kVAR=Required capacitor reactive power(kVAR)
kW=Real power of load(kilowatts)
φ₁=Current power factor angle(degrees)
φ₂=Target power factor angle(degrees)
PF=Power factor(dimensionless (0-1))
Worked Example
400 kW load at 0.72 PF, correct to 0.95 PF.
- φ₁ = arccos(0.72) = 43.95°, tan(43.95°) = 0.964
- φ₂ = arccos(0.95) = 18.19°, tan(18.19°) = 0.329
- kVAR = 400 × (0.964 − 0.329) = 400 × 0.635 = 254 kVAR
Answer: 254 kVAR capacitor bank needed (select 250 or 300 kVAR standard)
When to Use
- •Sizing power factor correction capacitor banks
- •Reducing utility power factor penalties
- •Freeing transformer and feeder capacity by reducing reactive power
- •Meeting utility PF requirements (typically >0.90)
Standards & References
- NEC 460 — Capacitors
- NEC 460.8 — Disconnect rated at 135% of capacitor current
- IEEE 1036 — Shunt Power Capacitor Application