Power Factor Correction Calculator

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.