Power and energy

Power-factor correction kvar calculator

Calculate the reactive-power reduction required to move a lagging sinusoidal load from one displacement power factor to a higher target.

Calculate

Load and target
kW
Ideal current comparison
V

Worked example

Capacitive kvar to add (ideal)

 kvar

Reactive power before correction (lagging)
225 kvar
Reactive power after correction (lagging)
 kvar
Apparent power before correction
375 kVA
Apparent power after correction
 kVA
Line current before correction, each line
 A
Line current after correction, each line
 A
Line-current reduction
 %

Balanced three-phase line current at 400 V. This arithmetic does not select or approve a capacitor bank; harmonic and resonance assessment is required.

Underlined figures are rounded. Select one to copy its full value.

Method and assumptions

Formula

Qc = P × [tan(cos⁻¹ PF₁) − tan(cos⁻¹ PF₂)]

This calculation is for lagging displacement power factor and sinusoidal or fundamental-frequency quantities. It does not derive a capacitor construction, voltage rating or switching scheme.

Limits of this result

  • Do not apply this displacement-power triangle to total power factor where harmonic distortion is material.
  • Harmonic spectrum, resonance, detuning, capacitor voltage/current stress, switching transients, step size, duty cycle and utility limits require an engineering study.
  • The entered voltage is used only to compare ideal line current before and after correction; it does not size a capacitor or protective device.
  • This mode assumes an initially lagging load and a higher lagging target; leading-power-factor correction is outside scope.

Technical sources

  1. Power factor correction and harmonic filtering in electrical plantsABB · Technical Application Paper 1SDC007107G0201, July 2008
  2. Electrical devices — electrotechnical formulasABB · 1SDC010001D0202

Put the value to work

Read the related engineering guidance, or carry this task into System Builder to identify the signal path and EpiSensor products.

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