How to use the Power Factor Correction Calculator
- 1. Enter the loadActive power in kW and the present power factor.
- 2. Set the targetTarget pf, supply type, voltage and frequency.
- 3. Get the bank sizekVAR, capacitance per phase and the reduction in current.
Power factor correction formula
The active power P stays the same; capacitors supply part of the reactive power. The capacitor rating is Qc = P (tan φ1 − tan φ2), where φ1 = cos⁻¹(pf now) and φ2 = cos⁻¹(target pf).
- Single phase: C = Qc / (2πf V²)
- Three-phase delta bank: C = Qc / (3 × 2πf VL²) per phase
- Three-phase star bank: C = Qc / (2πf VL²) per phase
Worked example: a 100 kW load at pf 0.7 is to be raised to 0.95. tan φ1 = 1.020 and tan φ2 = 0.329, so Qc = 100 × 0.691 = 69.2 kVAR. For a delta bank at 415 V, 50 Hz, C = 69,152 / (3 × 314.16 × 415²) = 426 µF per phase. Line current falls from 199 A to 146 A.
Why it matters and exam questions
A low power factor draws more current for the same useful power, so cables, transformers and switchgear run hotter and losses rise as I²R. Supply companies may charge extra for low power factor, so check your tariff.
- Find the kVAR needed to raise pf from 0.6 to 0.9 for a 5 kW single-phase load (4.25 kVAR).
- Find the capacitance per phase for star and delta banks.
- Compare kVA before and after correction.
- Why are delta banks smaller in µF than star banks?
Frequently asked questions
Why does a delta bank need less capacitance?
Each delta capacitor sees the full line voltage, while a star capacitor sees VL/√3. Reactive power goes with V², so delta needs one third of the µF.
Should I correct to unity power factor?
Usually not. Correcting to about 0.95 to 0.98 gets most of the benefit, and going to 1 or leading can cause over-voltage at light load.
Does correction reduce my kWh?
Not much. kWh depends on active power. Correction mainly reduces current, kVA demand and losses in cables.
Is this tool free?
Yes. You enter your name and WhatsApp number once to see your result, and all other Uncodemy tools then open without the form.