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Electrical

Three Phase Power Calculator

Real, apparent and reactive power on three phase.

Your measurementsEvery assumption editable01
PowerCalculated live02

Result

70.67kW

83.14 kVA apparent, 70.67 kW real

Line voltage277.1 V line to neutral
480 V
Line current
100 A
Apparent power√3 × V × I ÷ 1000
83.138 kVA
Real powerat 0.85 power factor
70.668 kW
Reactive power
43.796 kVAR
Phase angle
31.79°

Line voltage and phase voltage differ by √3 in a wye system — 480 V between lines is 277 V line to neutral. Confusing the two is the commonest three-phase error after forgetting the √3 entirely.

Reactive power does no useful work but still flows through the conductors and the transformer, which is why utilities charge large consumers for poor power factor. Correcting it with capacitors reduces current for the same real power.

The phase angle is simply the arccosine of the power factor — a 0.85 power factor is a 31.8 degree lag between voltage and current.

Line voltage, line current and power factor give all three power quantities. The line-to-neutral voltage is shown alongside, because confusing it with line-to-line is the second most common three-phase error.

Why use this tool?What it does differently03

Why use this tool?

All three quantities

kW, kVA and kVAR, which is what a power quality discussion actually needs.

Line and phase voltage

480 V between lines is 277 V to neutral — both shown.

Phase angle

The arccosine of power factor, for anyone working with vector diagrams.

Explains reactive power

Why utilities bill large consumers for poor power factor.

How this worksThe method04

How this three phase power calculator works

Apparent power in kVA is √3 times line voltage times line current, divided by a thousand. Real power is that times power factor, and reactive power is the remaining leg of the right triangle they form.

The √3 comes from the 120-degree phase relationship between the legs, and line voltage exceeds line-to-neutral voltage by the same factor. That is why 480 V systems have 277 V lighting circuits.

Reactive power does no useful work but still flows through conductors and transformers. Correcting it with capacitors reduces current for the same real power, which is why large consumers install correction equipment.

How to use itStep by step05

How to use it

  1. Step 1: Enter line voltage

    Line to line, which is how three-phase systems are named.

  2. Step 2: Enter line current

    Measured on one conductor.

  3. Step 3: Set power factor

    From the nameplate or a meter reading.

  4. Step 4: Check the phase voltage

    If you are working line to neutral rather than line to line.

Example usageWorked figures06

Example usage

A 480 V feeder
100 A at 0.85 power factor is 83.14 kVA apparent, 70.67 kW real and 43.80 kVAR reactive, with a 31.8° phase angle.
Line versus phase
That same 480 V system is 277 V line to neutral — which is why commercial lighting runs at 277 rather than 120.
Correcting power factor
Lifting 0.85 to 0.95 on the same 70.67 kW load drops apparent power to 74.4 kVA and the current with it, freeing capacity in the same conductors.
Frequently asked questionsCommon questions07

Frequently asked questions

How do I calculate three phase power?

√3 times line voltage times line current gives volt-amps. Multiply by power factor for watts. The √3 is roughly 1.732.

What is the difference between line and phase voltage?

They differ by √3 in a wye system. A 480 V three-phase supply is 277 V from any line to neutral.

What is reactive power?

Power that flows back and forth without doing useful work, caused by inductive loads like motors. It still occupies conductor and transformer capacity, which is why it is billed.

Why is power factor correction worth it?

Because it reduces current for the same real power, freeing capacity in existing conductors and avoiding utility penalties. On a large motor load the payback is often quick.

Does the √3 apply to delta as well as wye?

The power formula is the same for both. What differs is the relationship between line and phase quantities — in delta the currents differ by √3 rather than the voltages.

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