Reactive Power Calculator
Choose the known data method. Fill only the fields needed for that method. Extra fields can support estimates and correction sizing.
Formula Used
The calculator supports several standard reactive power paths. Use the one that matches your known measurements.
Q = V × I × sin(φ)for single phase circuits.Q = √3 × VL-L × IL × sin(φ)for balanced three phase circuits.φ = cos⁻¹(PF)converts power factor to phase angle.Q = √(S² − P²)from apparent and real power.Q = P × tan(cos⁻¹(PF))from real power and power factor.Q = S × sin(θ)from apparent power and angle.Q = I² × Xfrom current and reactance.Qc = V² × 2πfCfor capacitive reactive magnitude.QL = V² ÷ (2πfL)for inductive reactive magnitude.
Positive kVAR is treated as inductive. Negative kVAR is treated as capacitive.
How to Use This Calculator
- Select the method matching your available data.
- Enter voltage, current, power factor, angle, power, or component values.
- Choose lagging for inductive loads or leading for capacitive loads.
- Add a target power factor if you want correction sizing.
- Press calculate and review the result above the form.
- Download CSV for spreadsheet records or PDF for reports.
Example Data Table
| Case | Known data | Method | Expected result | Use note |
|---|---|---|---|---|
| Motor feeder | 480 V, 120 A, PF 0.82 | Three phase V, I, PF | 54.67 kVAR | Balanced load estimate |
| Panel meter | 75 kW, 100 kVA | Apparent and real power | 66.14 kVAR | Power triangle review |
| Capacitor bank | 480 V, 60 Hz, 120 µF | Capacitance method | -10.42 kVAR | Leading reactive supply |
| Reactor | 480 V, 60 Hz, 25 mH | Inductance method | 24.45 kVAR | Lagging reactive demand |
Understanding Reactive Power
Reactive power is the portion of electrical power that moves between the source and magnetic or electric fields. It does not perform direct work like heat, light, or motion. Yet it is required by motors, transformers, reactors, and many power electronic loads. The unit is VAR, kVAR, or MVAR. A positive value usually describes inductive demand. A negative value often describes capacitive supply. Knowing the sign helps engineers plan correction and avoid overcompensation.
Why Several Methods Are Useful
Reactive power can be found in more than one way because field data is not always complete. Sometimes you know voltage, current, and power factor. Sometimes a meter gives real power and apparent power. A protection study may provide impedance values. A capacitor bank schedule may provide capacitance and frequency. This calculator supports those cases. It gives one result method at a time, so the inputs stay clear.
Power Factor and Phase Angle
Power factor connects real power to apparent power. It equals the cosine of the phase angle. When the power factor is low, the angle is larger. Then the reactive component becomes larger. For a fixed real load, more reactive power means more current. More current can increase losses, voltage drop, cable heating, and transformer loading. Improving power factor can reduce those effects.
Single Phase and Three Phase Use
For single phase circuits, reactive power from voltage and current uses V times I times sine angle. For balanced three phase circuits, the line value uses square root of three times line voltage times line current times sine angle. These formulas assume sinusoidal steady state conditions. Harmonics, unbalanced loads, and distorted waveforms may need power quality instruments and deeper analysis.
Real and Apparent Power Method
If apparent power and real power are known, the power triangle gives reactive power. Apparent power is the hypotenuse. Real power is the horizontal side. Reactive power is the vertical side. The equation is the square root of apparent power squared minus real power squared. This is useful for generator sizing, transformer loading, and utility billing review.
Impedance, Capacitance, and Inductance
Reactive power can also be calculated from reactance. With current and reactance, the value is current squared times reactance. For capacitors, reactance depends on frequency and capacitance. For inductors, reactance depends on frequency and inductance. The calculator converts microfarads and millihenries, then reports the equivalent reactive power.
Using the Result Correctly
Use the result as an engineering estimate. Check voltage basis, current basis, frequency, and unit choices before making decisions. For three phase systems, enter line to line voltage unless your study uses another defined basis. For capacitor correction, compare present power factor with the target. Avoid choosing a target that causes leading power factor during light load. Always confirm final capacitor, reactor, and switchgear ratings with local standards and qualified personnel.
Practical Checks Before Export
After calculation, review the displayed angle, sine value, and method note. They show how the result was produced. If values look unusual, test another method with the same load data. Similar answers increase confidence. Large differences may reveal wrong units, a line voltage mistake, or a leading and lagging selection error. Save the CSV for spreadsheets. Use the PDF for records, maintenance notes, and quick sharing with a project team. Name each saved file with panel, feeder, date, and reviewer for clear traceability during audits later.
FAQs
What is reactive power?
Reactive power is electrical power exchanged with magnetic or electric fields. It supports motors, transformers, capacitors, and inductors. It is measured in VAR, kVAR, or MVAR.
Why is reactive power important?
Reactive power affects current flow, voltage drop, equipment loading, and power factor. Too much reactive demand can increase losses and reduce useful system capacity.
What does positive kVAR mean?
Positive kVAR usually means inductive or lagging reactive power. Motors, transformers, and reactors commonly draw positive reactive power from the supply.
What does negative kVAR mean?
Negative kVAR usually means capacitive or leading reactive power. Capacitor banks can supply negative reactive power to offset lagging inductive demand.
Which method should I choose?
Choose the method that matches your known data. Use voltage, current, and power factor for field readings. Use apparent and real power for meter data.
Can I use this for three phase loads?
Yes. Select the three phase method. Enter line to line voltage and line current for a balanced system. Unbalanced systems need phase by phase analysis.
What is power factor?
Power factor is the ratio of real power to apparent power. It also equals the cosine of the phase angle in sinusoidal steady state conditions.
Can the calculator size capacitors?
It can estimate capacitor kVAR when real power, present factor, and target factor are available. Final equipment sizing should follow engineering standards.
Does frequency affect reactive power?
Yes. Frequency changes capacitor and inductor reactance. Capacitance reactive power rises with frequency. Inductance voltage based reactive power falls as frequency rises.
What unit should voltage use?
Enter voltage in volts. For the three phase method, use line to line voltage unless your study clearly specifies a different voltage basis.
Can apparent power be lower than real power?
No. Apparent power is the power triangle hypotenuse. It must be equal to or greater than real power for valid standard calculations.
Why does low power factor increase current?
For the same real load, lower power factor requires higher apparent power. Higher apparent power usually means higher current and greater distribution losses.
Are harmonic loads included?
This calculator uses common sinusoidal formulas. Harmonic, distorted, or strongly unbalanced loads may need true power quality measurements and detailed analysis.
Can I export the result?
Yes. After calculation, use the CSV button for spreadsheet data. Use the PDF button for a simple record of the displayed result.