38 — 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
- —%
Please fill all fields with valid numbers.
- Opens the print dialog. Choose “Save as PDF” as the destination.
- Opens your email program with the values from this calculation. Nothing is sent to us until you send it yourself.
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.
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.
More tools
- 01Cable cross-section
- 02Voltage drop
- 03Cable resistance
- 04Cable losses
- 05Maximum cable length
- 06Current-carrying capacity
- 07Parallel cables
- 08Conductor temperature
- 09Cable capacitance
- 10Short-circuit current
- 11Cable impedance
- 12Network impedance
- 13Short-circuit current at the far end
- 14Thermal short-circuit withstand
- 15Length and disconnection
- 16Motor current
- 17Torque
- 18Starting current
- 19Star-delta starting
- 20Soft starting
- 21Motor efficiency
- 22Speed control instead of throttling
- 23Speed and slip
- 24Setting the motor protection
- 25Single-phase motor
- 26Motor feeder
- 27Required motor rating
- 28PFD and SIL
- 29PFH and SIL
- 30Protective conductor size
- 31Earth rod
- 32Touch voltage
- 33Residual current protection
- 34Check discrimination
- 35Connecting a surge arrester
- 36Enclosure cooling
- 37Reference designation
Contact
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