Calculators

Calculate reactive power compensation

Reactive power does no work but loads cables, transformers and switchgear and is billed by the grid operator. How much capacitor rating is needed to reach a given power factor is a single formula.

Result

Required compensation power: —kvar
Apparent power before: —kVA
Apparent power after: —kVA
Relief on the supply: —%

A guide, not a design to standard. We give no warranty for the correctness of the results. The applicable standards and case-by-case verification govern.

Calculated on

Calculate reactive power compensation

Inputs

Active power: kW
Present cos φ
Target cos φ

Result

Required compensation power: kvar
Apparent power before: kVA
Apparent power after: kVA
Relief on the supply: %

Formula

Qc = P · (tan φ₁ − tan φ₂)
φ = arccos(cos φ)
S = P / cos φ

Assumptions and standards

The calculation applies to the operating point you enter. With strongly varying load, an automatically controlled system is more suitable than fixed compensation.
With significant harmonic content, for example from drives, detuned capacitors are required, otherwise resonance can occur.
The relief figure refers to the apparent current in the supply cable.

A guide, not a design to standard. We give no warranty for the correctness of the results. The applicable standards and case-by-case verification govern.

FISEKON GmbH · Fischer Elektrokonstruktion · https://fisekon.com

The grey values are an example. Simply enter your own.

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Calculating is the easy part.

A formula gives you a number. Designing a plant also demands installation method, grouping, discrimination, the standards in force and a look at the installed base. That is what we take on.

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Method and questions

Reactive power compensation

Required capacitor rating for a target power factor.

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Worked example

The default case the calculator starts with, worked through once. Change the values above and it recalculates immediately.

Inputs

Active power: 150 kW
Present cos φ: 0.75
Target cos φ: 0.95

Result

Required compensation power: 83 kvar
Apparent power before: 200 kVA
Apparent power after: 158 kVA
Relief on the supply: 21.1 %

Formula and standards

Formula

Qc = P · (tan φ₁ − tan φ₂)
φ = arccos(cos φ)
S = P / cos φ

Assumptions and standards

The calculation applies to the operating point you enter. With strongly varying load, an automatically controlled system is more suitable than fixed compensation.
With significant harmonic content, for example from drives, detuned capacitors are required, otherwise resonance can occur.
The relief figure refers to the apparent current in the supply cable.

Which target cos φ should I choose?

Grid operators usually require at least 0.90. Designing for 0.95 is common. Compensating to 1.0 is mostly uneconomic and can lead to capacitive operation at partial load.

Can I overcompensate?

Yes. Overexcited operation, capacitive reactive power fed into the grid, is also objected to by grid operators and can cause voltage rise. That is why varying loads use controlled compensation.