Calculation
C = P·(tan φ1−tan φ2)/(2πf·U²)
The capacitor supplies the difference between original and target inductive reactive power.
Busch 2006, Abschnitt Blindleistungskompensation
Power Factor Correction Capacitor Calculator
The capacitor supplies the difference between original and target inductive reactive power.
MINTSI
02
Result
Select a target and calculate.
Required capacitance C versus target power factor cos φ₂
C = P·(tan φ₁ − tan φ₂)/(2π·f·U²). Because tan φ falls steeply to zero near cos φ = 1, the last step to full compensation costs a disproportionate amount of capacitance. In practice systems are usually compensated to about 0.95 rather than 1, which also avoids over-compensation and resonance.
No curve point selected yet.
Understand the inputs
- Required shunt capacitance C — Total effective capacitance connected in parallel with the single-phase load at the calculated operating point.
- Real power P — Average real power of the load at the steady operating point to be corrected.
- Initial power factor cos φ1 — Measured inductive displacement factor before the capacitor is connected.
- Target power factor cos φ2 — Desired displacement factor after correction; must exceed cos φ1 and not exceed 1.
- Capacitor RMS voltage U — Actual RMS voltage directly across the shunt capacitor.
- Supply frequency f — Frequency of the sinusoidal supply for which capacitance is sized.
Example
10 kW, cos φ1=0.75, cos φ2=0.95, 230 V and 50 Hz give Qc≈5.53 kvar and C≈333 µF.
Assumptions and limits
Single-phase sinusoidal inductive load at a constant operating point; three-phase connection, harmonics, resonance and switching stages are excluded.
Understand Power Factor Correction Capacitor Calculator
This calculator estimates shunt capacitance needed to move a single-phase inductive load from its existing to a target displacement factor at one fixed operating point.
What does this quantity describe?
Each cos φ is converted to tan φ. Required correction is Qc=P·(tanφ1−tanφ2), while a shunt capacitor supplies |Qc|=2πfCU² under sinusoidal voltage.
Formula and variables
C = P·(tan φ1−tan φ2)/(2πf·U²)
Qc = P · (tan φ1 − tan φ2)C = Qc/(2πfU²)
| Symbol / input | Meaning |
|---|---|
| Required shunt capacitance C | Total effective capacitance connected in parallel with the single-phase load at the calculated operating point. |
| Real power P | Average real power of the load at the steady operating point to be corrected. |
| Initial power factor cos φ1 | Measured inductive displacement factor before the capacitor is connected. |
| Target power factor cos φ2 | Desired displacement factor after correction; must exceed cos φ1 and not exceed 1. |
| Capacitor RMS voltage U | Actual RMS voltage directly across the shunt capacitor. |
| Supply frequency f | Frequency of the sinusoidal supply for which capacitance is sized. |
Choose the inputs correctly
P is simultaneous real power, cos φ1 the initial inductive displacement factor, cos φ2 a realistic target, U voltage directly across the capacitor, and f supply frequency.
How to use the calculator
Measure P and cos φ1 at the representative steady load, choose cos φ2 above cos φ1, and enter capacitor voltage and frequency. Check standard stages and overcorrection before rounding.
Worked example
Correcting 10 kW from 0.75 to 0.95 at 230 V and 50 Hz requires about 5.53 kvar capacitive or 333 µF.
Understand the result and units
C applies to this load point. At lower inductive load a fixed capacitor can overcorrect, so variable systems require staged or controlled banks.
P in W/kW, U in V, f in Hz and C with farad prefixes. Enter cos φ as a decimal, 0.95 rather than 95.
Typical applications
Preliminary sizing for single-phase motors and inductive lab loads, and learning the link between the power triangle and capacitor size.
Assumptions, limits and common mistakes
Not a three-phase capacitor-bank design. Star/delta connection, harmonic resonance, detuning, inrush, tolerance, ageing, fusing and discharge resistors are excluded.
Common mistake: Use voltage actually across the capacitor, not an unchecked line or phase voltage. Do not enter power factors as percentages or apply the model to an already capacitive load.
Frequently asked questions
What is “Power-factor correction capacitor” used for?
Preliminary sizing for single-phase motors and inductive lab loads, and learning the link between the power triangle and capacitor size.
Where do the input values come from?
P is simultaneous real power, cos φ1 the initial inductive displacement factor, cos φ2 a realistic target, U voltage directly across the capacitor, and f supply frequency.
What does the result not cover?
Not a three-phase capacitor-bank design. Star/delta connection, harmonic resonance, detuning, inrush, tolerance, ageing, fusing and discharge resistors are excluded.