Power Factor Correction (kVAr) Calculator
Calculate the total capacitor bank power (kVAr), the kVAr/kW factor and the reduction in line current needed to raise the existing power factor to the target cos φ.
Formula used
Qc = P × (tan φ₁ − tan φ₂) · Three-phase current: Ic = Qc / (√3 × U)
Reactive power factor table (kc = tan φ₁ − tan φ₂ · kVAr per kW)
Multiplier per 1 kW of active power to raise the existing power factor (cos φ₁) to the target power factor (cos φ₂). Required capacitor bank power: Qc = P × kc.
| Existing cos φ₁ | Target 0.95 | Target 0.96 | Target 0.98 | Target 1.00 |
|---|---|---|---|---|
| 0.60 | 1.005 | 1.042 | 1.130 | 1.333 |
| 0.65 | 0.840 | 0.877 | 0.966 | 1.169 |
| 0.70 | 0.692 | 0.729 | 0.817 | 1.020 |
| 0.75 | 0.553 | 0.590 | 0.679 | 0.882 |
| 0.80 | 0.421 | 0.458 | 0.547 | 0.750 |
| 0.85 | 0.291 | 0.328 | 0.417 | 0.620 |
| 0.90 | 0.156 | 0.193 | 0.281 | 0.484 |
Capacitor power and current by active power (400 V three-phase, cos φ 0.75 → 0.98)
Calculator results for three-phase 400 V when raising cos φ from 0.75 to 0.98. Harmonics, reactor tuning factor and capacitor voltage rating (440 V / 525 V) are assessed separately.
| Active power (kW) | Required Qc (kVAr) | Capacitor current (A) | Line current before (A) | Line current after (A) |
|---|---|---|---|---|
| 10 | 6.79 | 9.80 | 19.25 | 14.73 |
| 25 | 16.97 | 24.50 | 48.11 | 36.82 |
| 50 | 33.94 | 48.99 | 96.23 | 73.64 |
| 100 | 67.89 | 97.98 | 192.45 | 147.28 |
| 150 | 101.83 | 146.98 | 288.68 | 220.92 |
| 250 | 169.71 | 244.96 | 481.13 | 368.21 |
| 400 | 271.54 | 391.94 | 769.80 | 589.13 |
Example: 100 kW, 400 V three-phase load from cos φ 0.75 to 0.98
- Multiplier: for cos φ₁ = 0.75 and cos φ₂ = 0.98, tan φ₁ − tan φ₂ = 0.679 kVAr/kW.
- Required reactive power: Qc = 100 × 0.679 = 67.89 kVAr.
- Three-phase 400 V capacitor current: Ic = 97.98 A; line current drops from 192.45 A to 147.28 A.
How is power factor correction (kVAr) calculated?
Required reactive power is calculated with Qc = P × (tan φ₁ − tan φ₂), where P is active power (kW), φ₁ is the phase angle before correction and φ₂ is the target phase angle. For 100 kW raised from cos φ 0.75 to 0.98, kc = 0.679 and Qc = 67.89 kVAr.
How is capacitor bank reactive power calculated?
Required reactive power (kVAr) is found by multiplying active power (kW) by the difference between the tangents of the existing and target phase angles (tan φ₁ − tan φ₂).
What is checked when selecting capacitors and contactors?
In installations with harmonics, detuned filter reactors, capacitor voltage rating (440 V / 525 V), discharge resistors and capacitor duty contactors (AC-6b) must be assessed together.