Power Factor Correction Calculator

Find how many kVAr of capacitors raise the power factor to your target, the capacitance for each capacitor, and the line current saved.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Real power does the work. Reactive power moves back and forth and adds current without doing work. The capacitor kVAr needed is the real power times the difference between the tangents of the present and target phase angles.

The capacitance for each of three capacitors depends on how they are wired. In delta each one sees the line voltage; in star each sees the line voltage divided by root three.

Formulas used

  • Q_c = P(\tan\varphi_1 - \tan\varphi_2)
  • C = \dfrac{Q_c}{3\omega V^2}\ \text{(delta)}
  • Q = 3\omega C V^2

Worked example

With the default numbers in the calculator above:

  1. Present angle and its tangent: 1.02
  2. Target angle and its tangent: 0.33
  3. Capacitor kVAr needed: 69.15 kVAr
  4. Capacitance of each of the three capacitors (delta): 426.03 µF
  5. Apparent power before and after: 142.86 kVA then 105.26 kVA
  6. Line current before and after: 198.74 A then 146.44 A
  7. Current saved: 26.32 %

Change the numbers in the calculator to see the full working, every step, for your own case.

Common questions

What power factor should I aim for?

About 0.95 is a common target. Going much higher needs a lot more capacitance and risks over-correction at light load.

Can capacitors cause trouble?

Yes, where there are drives or other harmonic sources the capacitors can resonate with the supply. Ask a specialist about detuning reactors.

Related calculators

Further reading: Standard electrical engineering texts (power factor correction). Capacitor banks must be installed by a licensed person.

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