PFC

Engineering

Power Factor Correction Calculator

Calculate current and target kVA, kvar, and line current from fixed active power and two power factors. Quantify idealized correction kvar, apparent-demand reduction, and an entered kVA demand-charge difference.

Active load power (kW)Current power factorTarget power factorThree-phase line voltage (V)Monthly demand charge per kVAPlanning months

Current apparent power (kVA)-

Target apparent power (kVA)-

Current reactive power (kvar)-

Reactive power at target PF (kvar)-

Idealized capacitor correction (kvar)-

Current three-phase line current (A)-

Target three-phase line current (A)-

Apparent-power reduction-

Modeled demand-charge difference-

Decision view

Before-and-after power triangles

Before-and-after power trianglesA shared active-power base exposes the reactive, apparent-power, and line-current reductions created by the entered target.

Exact scenario comparisonTarget power factor changes while all other entered assumptions remain constant.

Target power factor	Current apparent power (kVA)	Target apparent power (kVA)	Current reactive power (kvar)	Reactive power at target PF (kvar)	Idealized capacitor correction (kvar)	Current three-phase line current (A)	Target three-phase line current (A)	Apparent-power reduction	Modeled demand-charge difference

How to use Power Factor Correction Calculator

Enter fixed active load power.
Enter present and target power factors.
Enter the three-phase line voltage.
Use the kvar correction as a planning value and interpret tariff savings separately.

Calculator guide

Understanding Power Factor Correction Calculator

Power-factor correction reduces reactive and apparent demand while leaving the active load power unchanged. This calculator compares the present and target power triangles and exposes the idealized capacitor kvar rather than treating the change as an energy-efficiency gain.

P stays fixed Correction does not reduce active load work.

Q shrinks Local compensation reduces reactive demand.

S follows Lower kvar reduces kVA.

Current follows kVA At fixed voltage, line current falls.

Calculation method

How the calculation works

Derive reactive power from active and apparent power before and after an entered power-factor target, then expose current and demand-charge effects. Divide active kW by each power factor for kVA, use the power triangle for kvar, subtract target kvar from current kvar, and convert kVA to three-phase current at the entered voltage.

Detailed calculation process

Hold active power constant while shrinking the reactive leg

The defaults correct a 180 kW load from PF 0.72 to PF 0.95 at 400 V.

General formula: S_1 = P/PF_1; S_2 = P/PF_2; Q_i = sqrt(S_i^2 - P^2); Q_c = max(0, Q_1-Q_2); I_i = 1000 S_i/[sqrt(3)V_L] Active power P stays fixed. A higher target power factor shortens both the reactive leg Q and apparent-power hypotenuse S, which also reduces line current at the same voltage.

What each symbol means

P Active load power, measured in kilowatts (kW).

PF_1 / PF_2 Current and target power factors, unitless.

S_1 / S_2 Current and target apparent power, measured in kVA.

Q_1 / Q_2 Current and target reactive power, measured in kvar.

Q_c Idealized capacitor correction, measured in kvar.

V_L / I Line-to-line voltage in V and calculated line current in A.

Worked substitution with the default inputs

1. Calculate present apparent power: S_1 = 180/0.72 = 250.000 kVA Low power factor requires more kVA for the same 180 kW.

2. Calculate target apparent power: S_2 = 180/0.95 = 189.4737 kVA The target reduces apparent demand by 60.5263 kVA.

3. Resolve both reactive legs: Q_1 = sqrt(250^2-180^2) = 173.4935 kvar; Q_2 = sqrt(189.4737^2-180^2) = 59.1631 kvar Both triangles share the same active-power base.

4. Size idealized correction: Q_c = 173.4935 - 59.1631 = 114.3304 kvar This is the theoretical reactive reduction before practical equipment selection.

5. Check current and modeled demand cost: I_1 = 360.844 A; I_2 = 273.482 A; savings = 60.5263 x 12 x 12 = 8,715.79 The cost difference applies only if billing follows the entered kVA charge.

The default correction reduces apparent demand from 250.000 to 189.474 kVA, line current from 360.844 to 273.482 A, and reactive demand by 114.330 kvar.

Before and after

Compare two power triangles on one active-power base

The target case shows exactly which electrical quantities shrink.

Same kW Useful active load is unchanged.

Less kvar Correction shortens the vertical leg.

Less kVA The hypotenuse becomes smaller.

Less current Conductor loading falls at fixed voltage.

Worked situations

Practical examples

A 180 kW load at PF 0.72 draws 250 kVA.
Raising PF to 0.95 reduces idealized current by about 87.362 A.
The idealized correction is 114.330 kvar.

Better inputs

Useful tips

Do not target unity PF without a system study.
Check utility billing before assigning savings.
Select staged equipment for variable loads when appropriate.

Before relying on the result

Limitations and common mistakes

Harmonics, resonance, switching, detuning, voltage rise, and motor behavior are excluded.
Actual capacitor-bank sizes use standard steps and engineering margins.
Energy charges usually do not fall solely from improving PF.

Reference

Key terms

Correction kvar: Reactive power supplied locally by correction equipment.
Power triangle: Right triangle relating kW, kvar, and kVA.
Demand charge: Charge based on a billing-period capacity measurement.

Important note

Calculated from the entered values using the displayed engineering relationship. Confirm design values, load cases, safety factors, standards, and field conditions with a qualified professional.

Frequently asked questions

Does correction reduce active kW?

The idealized calculation holds active load power constant.

Why not always choose PF 1.00?

Overcorrection, resonance, switching, and changing load conditions require engineering review.

Is Qc the installed bank rating?

It is an idealized need; practical selection uses available stages and system studies.

Why can savings be zero?

Utilities that bill only kWh may not reward reduced kVA directly.