🔋 ELECTRICAL

Power Factor Correction Calculator (Capacitor Bank Sizing)

Calculate required kVAr capacitor bank size to improve power factor and reduce electricity bills. IS 732 / IEEE 1459. Free tool.

📐 Standard: IS 732 / IEEE 1459
✅ Free to use
📄 PDF export
📱 Mobile friendly

ℹ️ About This Calculator

Low power factor means you draw more current from the grid than your actual working load requires, resulting in higher maximum demand (MD) charges on your electricity bill. Electricity boards in India (MSEDCL, BESCOM, TNEB etc.) impose penalty charges for PF below 0.90 and offer incentives for PF above 0.95. Installing a capacitor bank is the standard solution to correct power factor and reduce electricity costs.

Indian electricity tariff structures charge industrial and large commercial consumers for both kWh (energy) and kVA maximum demand. Improving power factor from 0.75 to 0.95 reduces the kVA demand by about 21% — directly reducing the demand charge component of the bill. Automatic Power Factor Correction (APFC) panels use contactors to switch capacitor stages in and out as the load varies, maintaining target PF continuously. Fixed capacitor banks are suitable only for steady loads.

📐 Power Factor Correction Formula

IS 732 / IEEE 1459

Required kVAr:
  Q_c = P × (tan φ₁ − tan φ₂)

Where:
  P    = Active load (kW)
  φ₁   = cos⁻¹(PF_existing)   [existing power factor angle]
  φ₂   = cos⁻¹(PF_target)     [target power factor angle]
  Q_c  = Capacitor bank rating (kVAr)

kVA Reduction:
  ΔkVA = P × (1/PF_existing − 1/PF_target)

Annual Saving Estimate:
  Savings = ΔkVA × Hours × Tariff_kVAh × Load Factor

❓ Frequently Asked Questions

What power factor penalty applies in India? +
Penalty structures vary by state. Typically: PF below 0.90 attracts a surcharge of 1–2% on energy charges per 0.01 below the limit. BESCOM (Karnataka) charges 1% surcharge per 0.01 below 0.90. MSEDCL (Maharashtra) offers 0.5% rebate per 0.01 above 0.90 up to 1.0. Check your state DISCOM tariff order for exact penalties.
What size capacitor bank do I need for a 100 kW load at PF 0.75? +
To correct from PF 0.75 to 0.95: Q_c = 100 × (tan(cos⁻¹0.75) − tan(cos⁻¹0.95)) = 100 × (0.8819 − 0.3287) = 55.3 kVAr. Select a 60 kVAr APFC panel (next standard size). The kVA demand reduces from 133 kVA to 105 kVA — a 21% reduction in MD charges.
Can I use capacitors to correct power factor for VFD-driven motors? +
No — never install fixed capacitors on the output side of a VFD (variable frequency drive). The VFD already corrects the input power factor. Installing capacitors can cause resonance and damage the VFD. If you have many VFDs and the overall plant PF is still low, install capacitors at the main incomer before the VFDs, or use active harmonic filters.
What is the difference between APFC and fixed capacitor banks? +
Fixed capacitor banks provide a constant kVAr regardless of load variation. Suitable only for constant loads. APFC (Automatic Power Factor Correction) panels sense the PF continuously and switch capacitor stages in or out via contactors to maintain the target PF. APFC is required for any load that varies significantly — which is most commercial and industrial installations.
Do capacitors affect harmonics? +
Yes — capacitors can amplify harmonic currents through resonance. If your facility has VFDs, UPS systems, or other non-linear loads generating significant harmonics (THD > 15%), standard capacitors may overheat and fail. Use de-tuned capacitor banks with series inductors (typically tuned to 189 Hz for 5th harmonic avoidance) or active harmonic filters.

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⚠️ Disclaimer: For preliminary engineering design only. Verify all results with a licensed engineer before use. Full disclaimer →

🔋 Power Factor Correction Calculator
Reference: IS 732 / IEEE 1459