APFC Capacitor Bank Sizing: kVAr Calculation Guide

Why Power Factor Correction?

Poor power factor results in:

• Penalty charges from electricity utility
• Higher current draw for same kW load
• Increased losses in cables and transformers
• Reduced effective capacity

kVAr Calculation

Formula

kVAr required = kW × (tan φ₁ - tan φ₂)

Where:

• φ₁ = arccos(existing PF)
• φ₂ = arccos(target PF)

Example

• Connected load: 500 kW
• Existing PF: 0.75
• Target PF: 0.99
• kVAr = 500 × (tan(41.4°) - tan(8.1°)) = 500 × (0.882 - 0.142) = 370 kVAr

Stage Sizing

APFC panels switch capacitor stages automatically:

• Minimum step: Usually 25 kVAr
• Total stages: 6, 8, or 12 stage relay
• Step ratio: Equal or 1:2:2 ratio

Standard Bank Sizes

150, 200, 250, 300, 400, 500, 600 kVAr

Detuned Reactors

For installations with harmonics (VFDs, rectifiers):

• 7% detuned reactor (tuned to 189 Hz) for typical harmonic content
• 14% detuned reactor for high harmonic environments
• Prevents capacitor resonance and premature failure

APFC Relay Selection

• Stages: 6, 8, or 12
• Sensitivity: 0.01 (minimum step / CT ratio)
• Response time: 30-90 seconds
• Power supply: 230V AC

Use Our Calculator

Try the PF Correction Calculator in our Engineering Tools Hub, or design a complete APFC panel with the AI Panel Builder.

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