Power Factor Correction Calculator

Parameters

Seven fields appear on the form. Only three of them change the numbers, a fourth changes a single recommendation, and the remaining three change nothing at all. That is worth stating plainly up front so you are not looking for an effect that is not there.

Active power

The real power the installation draws, in kilowatts. Form range 1 to 10000, default 100. Every kilovolt-ampere reactive figure scales directly with it, so it is the single most important input on the page. Take it from a demand meter, a power quality logger or the sum of connected loads with diversity applied. Gotcha. Use the kilowatts that coincide with the power factor you enter, ideally a peak demand interval. A yearly average kilowatt figure paired with a worst case power factor will size a bank that overcorrects for most of the year.

Current power factor

The measured, uncorrected power factor. Dimensionless, form range 0.1 to 0.99, default 0.75. Typical uncorrected values are 0.65 to 0.80 for a motor-heavy factory, 0.80 to 0.90 for a commercial building with chillers and air handling, and above 0.95 where loads are largely resistive. Gotcha. Use a measured value, not a nameplate one. Also be aware whether your meter reports displacement power factor or true power factor. On a site with drives and switching supplies the two differ, and capacitors correct only the displacement component. Correcting to a true power factor target with capacitors alone will not work.

Target power factor

The power factor you want after correction. Dimensionless, form range 0.9 to 0.99, default 0.95. Most Australian distributors set 0.90 as the threshold below which demand penalties apply, so 0.95 is a common target because it leaves margin. Gotcha. Do not chase unity. The kilovolt-ampere reactive required climbs steeply above about 0.97 for very little further reduction in apparent power, and a fixed bank sized to unity at peak will push the site leading at light load, which raises voltage and can be penalised in its own right. Entering a target below the current power factor produces a negative requirement, which the tool clamps to zero.

Supply voltage

Selectable as 230, 400, 415 or 11000 V. Gotcha. This field changes no result. Reactive power compensation in kilovolt-amperes reactive is independent of voltage, so the required kilovolt-amperes reactive is the same at 400 V as at 11 kV. It matters enormously to the physical capacitors you buy, because the capacitance in microfarads and the voltage rating both depend on it, but this tool does not calculate either.

Supply phase

Single phase or three phase. Gotcha. This field also changes no result. The total kilovolt-amperes reactive required is a whole-of-supply figure either way. It does not tell you how to split a bank across three phases, and it does not check that a single-phase site could physically accommodate the bank size returned.

Frequency

Selectable as 50 Hz or 60 Hz. Gotcha. This field changes no result either, including the detuning frequency, which is reported as a fixed 189 Hz whichever option you pick. That figure corresponds to a roughly 7 per cent detuned reactor on a 50 Hz supply. On a 60 Hz supply the equivalent tuning point is different and the 189 Hz shown is simply wrong.

Significant harmonics

A checkbox for sites with variable speed drives, rectifiers or large switching power supplies. Ticking it turns on a detuning recommendation, but only when the required compensation exceeds 20 kilovolt-amperes reactive. Gotcha. It is a yes or no flag, not a harmonic study. It does not ask for total harmonic distortion, individual harmonic magnitudes, transformer impedance or short circuit level, so it cannot tell you whether resonance will actually occur or which harmonic order is at risk. Leaving it unticked on a site that does have harmonics changes nothing about the kilovolt-amperes reactive result.

Assumptions and limits

What the tool assumes

• A single steady operating point. One kilowatt figure and one power factor. There is no load profile, no daily or seasonal variation and no distinction between a fixed bank and an automatic multi-stage panel. A real site swings across a wide range and the correct answer is usually a staged design, which this tool does not produce.
• Purely displacement power factor. The maths is the standard trigonometric relationship, required kilovolt-amperes reactive equals active power multiplied by the difference between the tangent of the present phase angle and the tangent of the target phase angle. That relationship only holds for the fundamental. Harmonic distortion is not modelled anywhere in the numbers.
• Lagging power factor throughout. Both power factors are treated as lagging and correction is always assumed to be capacitive. A site already leading is not handled.
• The bank rounds up to a standard size. The selection comes from the series 5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, 125, 150, 200, 250, 300, 400 and 500 kilovolt-amperes reactive, always choosing the first entry at or above the requirement. That deliberately overcorrects, sometimes by a lot on small requirements, and the tool does not warn you about the resulting leading power factor at light load.
• The current saving figure is a current reduction, not money. It is one minus the ratio of the two power factors, expressed as a percentage. It is the percentage reduction in apparent power and therefore in line current. It is not a reduction in your energy bill, because kilowatt hours do not change. Any dollar saving comes from demand charges and penalty structures that vary by distributor and tariff and are not modelled here.
• Nothing physical is designed. No capacitance in microfarads, no capacitor voltage rating, no step sizes, no switching contactors or thyristor modules, no discharge resistors, no protection, no bank cable sizing, no enclosure rating and no harmonic filter design.

What the compliance checks actually check

Two checks run. The first confirms your target power factor is at least 0.90, which is a check on what you typed rather than on the installation. The second confirms the selected bank is at least the required kilovolt-amperes reactive, which passes by construction because the selection always rounds up. It can only fail when the requirement exceeds 500 kilovolt-amperes reactive and the tool runs off the end of its own table. Neither check tests resonance, voltage rise, overcorrection at light load, capacitor duty or anything in AS/NZS 61000.3.100 beyond the target value itself.

What this must not be used for

• Final capacitor bank design, including step sizing, switching scheme, controller settings, protection or the bank subcircuit.
• Any decision about detuned reactors or harmonic filters. That requires a measured harmonic spectrum and a resonance study against the actual supply impedance.
• Sites with significant harmonic distortion where true power factor rather than displacement power factor is the problem. Capacitors do not correct distortion power factor and can make it worse.
• Estimating a financial payback. The current saving percentage is not a bill saving.
• Correcting individual motors at the starter, which needs the motor's magnetising current so the capacitor does not self-excite the machine on coast down.
• Evidence of compliance. This calculator is not validated or certified. Check every result against the current edition of AS/NZS 61000.3.100, your distributor's connection requirements and a site harmonic assessment, and have it signed off by the person responsible for the installation.

Worked examples

Three examples covering three-phase and single-phase supplies, with and without harmonics, and one that shows the round-up behaviour clearly. The tangent values below are the tangent of the arc cosine of each power factor, which is what the calculator computes internally.

Power Factor Correction Guide for AS/NZS 61000.3.100

Power factor correction is the process of adding capacitors (or other reactive compensation equipment) to an electrical installation to reduce the reactive power drawn from the supply network. In Australia, supply authorities penalise sites that operate with a power factor below 0.90 through demand charges on the excess kVA. For industrial and commercial sites with significant motor loads, power factor correction is one of the most cost-effective electrical upgrades available, often paying for itself within 12 to 18 months through reduced electricity bills.

This calculator determines the capacitor bank size (in kVAR) needed to raise an existing power factor to a target value. Enter your site's real power consumption, current power factor, and desired target. The calculator computes the required reactive compensation and shows the reduction in apparent power (kVA) and line current that results from the correction.

Key concepts

• Real, reactive, and apparent power. Real power (kW) does useful work. Reactive power (kVAR) sustains the magnetic fields in motors and transformers but performs no useful work. Apparent power (kVA) is the vector sum of real and reactive power, and it is what the supply network must deliver. Power factor is the ratio of kW to kVA. A power factor of 0.80 means only 80% of the apparent power is doing useful work.
• Why low power factor costs money. The supply authority sizes transformers, cables, and switchgear based on kVA, not kW. A site drawing 200 kW at 0.70 power factor requires 286 kVA from the network, while the same 200 kW at 0.95 power factor only requires 211 kVA. The extra 75 kVA wastes network capacity and increases I squared R losses in cables. Most Australian tariffs charge a demand penalty when power factor falls below 0.90.
• Capacitor correction principle. Capacitors generate leading reactive power that cancels the lagging reactive power drawn by inductive loads. The net reactive power seen by the supply decreases, which reduces apparent power and improves the power factor. Capacitors can be installed at the main switchboard (bulk correction) or at individual motor starters (point-of-load correction).
• Harmonic resonance risk. A capacitor bank and the supply transformer inductance form a parallel resonant circuit. If the resonant frequency aligns with a harmonic present on the network (commonly the 5th harmonic at 250 Hz), harmonic currents can amplify and damage equipment. Detuned reactors, rated at 7% or 12.5% impedance, are installed in series with capacitors to shift the resonant frequency below the lowest significant harmonic.

Common scenarios

• Manufacturing facility with motor loads. A factory running multiple induction motors typically has a natural power factor between 0.65 and 0.80. Installing a bulk capacitor bank at the main switchboard to correct to 0.95 reduces the site's kVA demand, lowers the electricity bill, and frees up capacity on the existing transformer for future loads. An automatic power factor correction (APFC) panel is preferred because the motor load varies throughout the day.
• Commercial building HVAC systems. Large air-handling units and chiller compressors are inductive loads that pull the building's power factor down during peak cooling periods. Seasonal load variation makes fixed capacitor banks unsuitable because they can overcorrect during light-load periods (leading to a leading power factor, which can cause voltage rise). An APFC system with multiple switched stages is the standard solution for these installations.
• Transformer capacity recovery. A site with a fully loaded 1000 kVA transformer at 0.80 power factor is drawing 800 kW. Correcting to 0.95 reduces the apparent demand to 842 kVA, freeing approximately 158 kVA of transformer capacity. This can defer or eliminate the need for an expensive transformer upgrade when adding new loads to the site.