Power factor correction for industrial facilities
A poor power factor inflates demand charges and loads your distribution for no useful work. How power factor correction works, how to size a capacitor bank, and when to use detuned reactors.
Al Sanaya Engineering
·8 min read
Inductive loads — motors, transformers, welding sets — draw two kinds of power. Active power does the useful work; reactive power magnetises the equipment and does none, but still flows through every transformer, cable and busduct between the load and the supply. Power factor correction cancels most of that reactive demand locally, and on an industrial site it pays for itself quickly.
Why a poor power factor costs money
Reactive power inflates the apparent power (kVA) drawn for a given useful load. That has two costs. First, many GCC utility tariffs bill on kVA demand or apply a low-power-factor penalty, so the bill rises for no extra production. Second, the extra current consumes capacity in your own transformers, switchgear and cables — capacity you would otherwise use for real load.
How correction works
Capacitors draw leading reactive power, which cancels the lagging reactive power of inductive loads. Install a capacitor bank near the load centre and the reactive current circulates locally instead of being drawn all the way from the supply.
Because site load varies through the day, the bank is divided into steps. An automatic power factor controller (APFC) switches steps in and out to hold the power factor near the target without over-correcting.
Sizing the capacitor bank
Sizing starts with the site's active power and its present power factor. From those, you calculate the reactive compensation (kVAr) required to reach the target — typically around 0.95. The total is then split into sensible steps so the controller can track the load smoothly.
- Establish active power (kW) and present power factor
- Set a realistic target — commonly 0.95
- Calculate the kVAr needed to close the gap
- Divide into steps suited to how the load actually varies
- Locate the bank near the load centre, not just at the main board
Harmonics and detuned reactors
Modern plants are full of electronics — variable speed drives, UPS systems, LED lighting — and these inject harmonic currents. Plain power factor capacitors can form a resonant circuit with the supply at a harmonic frequency, drawing amplified current that overheats and fails the bank.
The fix is a detuned reactor in series with each capacitor step. It shifts the resonant point below the lowest significant harmonic, so the bank corrects power factor without becoming a harmonic sink. On any site with meaningful drive or UPS load, a detuned bank is the safe default.
Maintenance
Capacitors age, contactors wear, and a failed step quietly erodes the correction you paid for. Periodic checks of capacitor health, step switching, controller settings and reactor temperature keep the bank delivering — and a thermographic survey will catch a hot contactor before it fails.
How Al Sanaya can help
We carry out power factor studies, size and supply capacitor banks and APFC panels — detuned where harmonics demand it — and support installation and maintenance for industrial facilities across the GCC and MENA.
Frequently asked questions
What is power factor in simple terms?
Power factor is the ratio of useful (active) power to total (apparent) power. Motors, transformers and other inductive loads draw extra reactive power that does no work but still has to be carried by the supply. A power factor near 1.0 means almost all the current is doing useful work.
How does power factor correction save money?
Many utility tariffs charge for apparent power (kVA) or penalise a low power factor. Correcting the power factor reduces the kVA drawn for the same useful load, lowering demand charges and freeing capacity in transformers and cables.
How is a capacitor bank sized?
From the site's active power (kW) and existing power factor, you calculate the reactive power (kVAr) needed to reach the target power factor — usually around 0.95. The bank is then split into steps so an automatic controller can switch capacitance in and out as the load varies.
When are detuned reactors needed?
Where the installation has significant harmonic content — from variable speed drives, UPS systems or other electronics — plain capacitors can resonate with the supply and be overloaded. Detuned reactors in series with the capacitors shift the resonant frequency clear of the harmonics and protect the bank.
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