05 — Tools
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
- —%
Please fill all fields with valid numbers.
A guide, not a design to standard. The applicable standards and case-by-case verification govern.
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
- 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.
Frequently asked
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.
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.
Contact
Tell us what it is about.
A phone call or three lines is enough. From the very start you talk to the people who will later work on your project – not to a distribution list.
Direct
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- Emailinfo@fisekon.com
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33332 Gütersloh
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