Calculation sequence
Step-by-step method
- Calculate initial and target reactive-power ratios.
- Subtract the target ratio from the initial ratio.
- Multiply by real power for ideal capacitive kvar.
ElectricalAdvancedPower Quality
Power-Factor Correction Screening Calculator
Estimate ideal capacitive kvar required to move a steady lagging load from an initial to a target power factor.
Why it matters: An ideal kvar screen is useful for planning, but actual capacitor application requires harmonic, resonance, switching, and utility analysis.
Calculated result
Engineering evaluation
Ideal correction requirement (Qᶜ)42.132 kvar
- Initial apparent power (S₁)
- 125 kVA
- Target apparent power (S₂)
- 105.263 kVA
Engineering interpretation
The ideal fundamental-frequency screen is 42.13159 kvar to move 100 kW from PF 0.8 to 0.95.
Important limitations
- Do not select or apply capacitors from this result alone. Harmonics, resonance, switching, voltage, fault duty, utility rules, and light-load leading PF require qualified electrical-engineer review.
Engineering knowledge center
Understand the calculation—not just the answer
Governing relationships
Qᶜ = P[tan(cos⁻¹PF₁)−tan(cos⁻¹PF₂)]
S₁ = P/PF₁
S₂ = P/PF₂
Current substitution
Qᶜ = 100[tan(cos⁻¹0.8)−tan(cos⁻¹0.95)] = 42.13159 kvar; S₁ = 125 kVA; S₂ = 105.2632 kVA.
Equation legend
Inputs and calculated quantities
- P
- Real power — kW
- PF₁
- Initial lagging power factor — 0–1
- PF₂
- Target power factor — 0–1
- Qᶜ
- Ideal correction requirement — kvar
- S₁
- Initial apparent power — kVA
- S₂
- Target apparent power — kVA
Applications
How this calculation is used
Building design
Screen the magnitude of a possible correction requirement.
Construction
Check that proposed correction is based on the correct load and voltage boundary.
Commissioning
Compare measured initial PF with a user-entered target without selecting equipment.
Quality controls
Assumptions and limitations
Assumptions
- The initial load is lagging and reasonably steady.
- The result represents ideal fundamental-frequency compensation only.
Limitations
- Does not select capacitors or evaluate harmonics, resonance, switching, voltage rise, fault duty, or light-load leading PF.
- Utility requirements, equipment data, and qualified electrical-engineer review are mandatory before application.
Field use
Verification procedure
- Follow the approved electrical-safety program and use correctly rated instruments.
- Confirm wiring, ratios, units, operating mode, and measurement boundaries.
- Document simultaneous readings and compare with approved project and manufacturer data.
Common engineering mistakes
- Combining values from different time intervals, phases, or measurement boundaries.
- Treating a screening result as equipment selection, protective-device coordination, or code compliance.
Technical basis
References and source standards
- IEEE Standards AssociationPower quantity, harmonic, transformer, motor, battery, and metering standards; verify the current applicable edition during professional review.
- NFPA 70, National Electrical CodeThe legally adopted edition and local amendments govern final electrical work; this library does not reproduce protected tables or establish compliance.
Engineering calculation disclaimer
These engineering tools are provided for educational, preliminary evaluation, field verification, and commissioning support. Results depend on the accuracy of user-entered information and the assumptions stated for each calculation. Every colored status and comparison is a screening indicator only; project criteria, contract requirements, applicable codes, manufacturer instructions, measurement uncertainty, and authorized engineering judgment govern. The tools do not replace project-specific engineering analysis or the judgment of a licensed professional engineer.
Read the full use and limitation statement