The question
A plant meter on an incomer logs two quantities all day. It logs current in amps and power factor. A power factor correction study needs three other quantities. It needs the apparent power in kVA, the real power in kW and the reactive power in kvar. Those three come from the two logged values and the voltage.
The inputs
- Phases: 3
- Voltage: 400 V
- Current: 120 A
- Power factor: 0.82
The current is the line current, not the phase current. The voltage is the line to line voltage. Both match what a clamp meter and a standard three‑phase meter report.
The clause
AS/NZS 3000:2018 Cl 2.2.2 sets maximum demand as the basis for sizing the supply. A demand figure in kVA comes from the same arithmetic used here. Cl 2.2.2 accepts measurement as one way to establish that demand on an existing installation.
The steps
The tool multiplies the line voltage by the line current, then by the square root of three.
- Apparent power: 83.14 kVA
It multiplies the apparent power by the power factor to get the real power.
- Real power: 68.17 kW
It takes the remaining leg of the power triangle for the reactive power.
- Reactive power: 47.59 kvar
The result
The incomer draws 83.14 kVA and delivers 68.17 kW of useful work. The gap between those two figures is the 47.59 kvar the plant circulates without turning it into output.
A correction study starts from that kvar figure. Raising the power factor towards 0.95 leaves the 68.17 kW untouched. The kVA falls, and the current falls with it. Size the capacitor bank from the kvar to be removed. That is the difference between the present 47.59 kvar and the kvar allowed at the target power factor.
What the numbers change
Three things follow a lower apparent power.
Cable heating falls with the square of the current. A modest drop in current makes a larger cut in the losses in the incoming cable.
Transformer headroom rises. A transformer is rated in kVA, so the correction releases capacity for new load without a new transformer.
Network charges often follow kVA or a power factor penalty. The tariff decides whether the study pays for itself.
Where the reading can mislead
A meter that averages over a long window hides the peaks. A drive-heavy plant swings between a light power factor at low speed and a better one at full load. Take the logged interval into account before a bank is fixed in size.
Harmonic current also inflates the measured current on a true RMS meter. The extra current is real and it heats the cable. It does no work. A plain capacitor bank does not correct it, and a detuned reactor belongs in that case.
Checking the reading
Three checks keep the figures honest before a bank is ordered.
Confirm the voltage at the meter. A nominal 400 V and a measured 415 V give different kVA for the same current. Log the voltage alongside the current.
Confirm the power factor sign. A leading power factor and a lagging power factor read the same on a meter that reports magnitude only. A site with existing capacitors can already lead at night.
Confirm the balance across the three phases. This tool takes one current for a balanced load. A site with single‑phase load spread unevenly needs the worst phase checked on its own.
This page is a design aid. Verify every value against the current edition of the standard.
See also: Three‑phase power: kVA to amps at 400 V, Commercial kitchen kW to amps full load current and Harmonics and neutral sizing.