Work out the capacitor bank you need to lift your power factor, how to split it into steps, and what it actually buys you — lower current, cooler cables and spare capacity in a transformer you thought was full.
Both numbers are on your electricity bill. If you cannot find the power factor, pick your type of site below and we will use a typical figure to get you started.
Going too far is a real mistake — overcorrecting pushes the power factor leading, which upsets voltage regulators and can be worse than doing nothing.
These two questions decide whether you need a plain capacitor bank or a detuned one — and getting it wrong is how capacitor banks explode.
This is the capacitor bank your site needs. Send it to us for a price, or go back and change the target to see the trade-off.
This calculator gives an indicative capacitor bank size for budgeting and comparing quotations. It is not a design document. Capacitor bank selection, harmonic assessment, protection and switching control must be confirmed by a qualified electrical engineer, ideally with a power quality measurement at the switchboard. Incorrectly applied capacitors can resonate with supply harmonics and fail destructively. Mega Standard accepts no liability for decisions made on these figures alone.
The kVAr arithmetic here is exact, not interpolated from a table. The judgement calls are the detuned-reactor threshold and the generator interlock, both of which should be confirmed by measurement at your switchboard.
Every motor and transformer on your site needs two kinds of current. One does the work — turning the shaft, heating the element. The other builds the magnetic field, and it is borrowed from the supply and handed back every cycle, fifty times a second.
That borrowed current does no useful work at all. But it is still real current: it still flows down your cables, still heats them, still fills up your transformer and still shows on your meter as apparent power. Power factor is simply the ratio between the useful part and the total.
At a power factor of 0.70, roughly a third of the current you are pulling achieves nothing. You paid for the cable that carries it and the transformer that supplies it.
A capacitor does the opposite of a motor: it supplies reactive current instead of consuming it. Put capacitors next to the motors and the borrowed current shuttles back and forth locally, instead of travelling all the way from the transformer.
Four things follow from that:
Unlike cable sizing, there is no interpolation and no reference table here. The kVAr you need falls straight out of trigonometry:
Qc = P × (tan φ₁ − tan φ₂) P = your load in kW φ₁ = arccos(present power factor) φ₂ = arccos(target power factor)
A 100 kW load at 0.75 needing 0.95 requires 100 × (0.882 − 0.329) = 55.3 kVAr. That number is not an estimate. The judgement in this tool is everything around it — the step arrangement, the harmonics and the generator interlock.
Harmonics. This is the one that destroys equipment. Variable speed drives, UPS rectifiers, LED drivers and welding sets all draw distorted current. A capacitor bank and the supply transformer's inductance form a resonant circuit, and if that circuit happens to resonate near one of the harmonic frequencies present — the fifth and seventh are the usual culprits — the harmonic current is amplified, sometimes several times over. The capacitors overheat and fail, occasionally violently.
The fix is a detuned bank: a reactor in series with each capacitor step, sized to put the resonant point below the lowest significant harmonic. A 7 % reactor tunes to about 189 Hz, safely under the 250 Hz fifth harmonic. Above roughly 15 % electronic load, detuned is not optional.
Generators. A capacitor bank sized for the mains will overcorrect a generator, because the generator sees a much smaller load. Leading power factor makes an alternator's automatic voltage regulator unstable, and the terminal voltage can run away. Any site that runs on a generator needs the capacitor steps interlocked to drop out when the changeover switch moves.
It depends only on your load in kW, your present power factor and your target. Enter those above and the calculator gives you the exact figure plus a sensible step arrangement. As a rough guide, correcting a 100 kW load from 0.75 to 0.95 takes around 55 kVAr.
It removes any power factor penalty your utility charges, and it slightly reduces the losses in your own cables. It does not reduce the actual kWh your equipment consumes — the useful energy is unchanged. The bigger financial benefit is usually the released transformer and cable capacity, which can let you expand without a substation upgrade.
A fixed bank suits a load that is roughly constant, or correction applied directly at a large motor. An automatic bank with several switching steps suits a varying load, because it can trim the correction as the load changes and avoid overcorrecting when the site is quiet. Most industrial installations use automatic.
If a significant share of your load is electronic — variable speed drives, UPS units, welding sets, large LED installations — then yes. Above roughly 15 % of total load, a plain capacitor bank risks resonating with the supply and failing. A power quality measurement at your switchboard settles it definitively and is inexpensive.
Not without control. A bank sized for the mains load will overcorrect a lightly loaded generator, and the resulting leading power factor makes the alternator's voltage regulator unstable. Standard practice is to interlock the capacitor steps so they disconnect on generator supply, or to allow only the smallest steps.
We supply Schneider and Legrand power factor correction equipment across Iraq — capacitors, controllers, contactors and detuned reactors, built into a panel or supplied loose. Send us the result and we will come back with a specification and a price, and tell you if a harmonic measurement is needed first.