Capacitor Bank kVAr to µF Calculator (3-Phase)

How to use the capacitor bank kVAr calculator

Enter the bank’s kVAr rating, the line voltage it is connected to, the frequency and whether the capacitors are connected in delta or star. The calculator returns the capacitance needed in each phase, the line current and the reactance of each capacitor. To work out the kVAr of an existing bank, enter the measured µF per phase and clear the kVAr field.

kVAr to µF formulas

Delta: C = Q ÷ (3 × 2πf × V_L²)  ·  Star: C = Q ÷ (2πf × V_L²)

I_L = Q ÷ (√3 × V_L)  ·  X_C = 1 ÷ (2πf C)

For a single-phase capacitor, C = Q ÷ (2πf × V²) and I = Q ÷ V.

Example

A 50 kVAr delta-connected bank on a 415 V, 50 Hz supply:

• C = 50,000 ÷ (3 × 314.16 × 415²) = 308.0 µF per phase (a star bank would need 924.1 µF)
• I = 50,000 ÷ (1.732 × 415) = 69.6 A
• X_C = 1 ÷ (314.16 × 308.0 µF) = 10.33 Ω

Capacitance and current at 415 V, 50 Hz

Output at reduced voltage

Capacitor output varies with V². For a bank rated 50 kVAr at its rated voltage:

Practical notes

• Size cables and switchgear for about 1.3–1.5 × rated current to allow for harmonics and capacitance tolerance.
• Where the THD is high, use detuned (reactor) banks to avoid resonance.
• Find the kVAr you need from the load and power factors with the power factor correction calculator.

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