Capacitor Bank Sizing Calculator

Calculator Inputs

Example Data Table

These are illustrative cases for quick comparison.

Case	Load kW	Voltage V	Present PF	Target PF	System	Connection	Suggested Bank	Capacitance per Phase
Industrial Motor Group	250	415	0.78	0.95	Three phase	Delta	125 kVAR	770.09 µF
HVAC Chiller Plant	180	400	0.82	0.96	Three phase	Delta	100 kVAR	663.15 µF
Single Phase Workshop	90	230	0.72	0.93	Single phase	—	75 kVAR	4512.90 µF

Formula Used

1) Power factor angles
φ₁ = cos⁻¹(Present PF)
φ₂ = cos⁻¹(Target PF)

2) Existing and target reactive power
Existing kVAR = kW × tan(φ₁)
Target kVAR = kW × tan(φ₂)

3) Capacitor bank requirement
Raw kVAR Required = Existing kVAR − Target kVAR
Adjusted kVAR Required = Raw kVAR × (1 + Safety Margin)

4) Rounded standard bank size
Recommended kVAR = ceil(Adjusted kVAR ÷ Step Size) × Step Size

5) Line current
Three phase current = (kW × 1000) ÷ (√3 × V × PF)
Single phase current = (kW × 1000) ÷ (V × PF)

6) Capacitance
Three phase delta: C = Q ÷ (3 × 2πf × V²)
Three phase star: C = Q ÷ (2πf × V²)
Single phase: C = Q ÷ (2πf × V²)
Here, Q is in VAR and C is in farads.

How to Use This Calculator

Select whether your installation is single phase or three phase. For three phase systems, choose delta or star connection.

Enter the active load in kilowatts, the operating voltage, frequency, and the current measured power factor.

Set your target power factor, then add demand factor, future growth, and safety margin to size the bank more realistically.

Enter a practical step size if you want an automatic stepped bank. Use annual hours and energy rate for savings estimates.

Click the calculate button. Review the bank size, capacitance, current reduction, achieved power factor, graph, and export files.

FAQs

1. Why do I need a capacitor bank?

A capacitor bank supplies reactive power locally. This raises power factor, lowers current, reduces losses, and can help avoid utility penalties or oversized upstream equipment.

2. What is the difference between fixed and automatic banks?

A fixed bank provides one constant correction value. An automatic bank switches steps in and out, making it better for varying loads and changing daily demand patterns.

3. Why is the recommended bank larger than the raw requirement?

The calculator adds your safety margin, then rounds up to the nearest standard step size. This produces a practical bank rating that can actually be purchased and installed.

4. What happens if I overcorrect power factor?

Too much capacitance can push the system into leading power factor. That may create voltage rise, poor regulator behavior, and switching issues in sensitive installations.

5. Should I use delta or star connection?

Delta is common for three phase low voltage capacitor banks because each unit sees line voltage. Star may be chosen for specific design, insulation, or protection preferences.

6. Are the energy savings exact?

No. The savings are estimates based on current reduction and your entered network loss percentage. Real savings depend on load profile, cable impedance, and operating conditions.

7. Does this calculator include harmonic detuning?

No. It sizes the capacitor bank for reactive power correction. Harmonic studies, detuned reactors, and resonance checks should be completed separately for nonlinear loads.

8. Can I use this for generator-backed systems?

Yes, but be careful. Generator systems often need tighter correction limits, switching control, and harmonic review because they can respond differently than utility-fed installations.