Generator Load Bank Calculator — kW, kVAR, kVA…

Resistive and reactive load-bank sizing model

Plan the electrical capacity of a generator load-bank test without confusing engine kW loading with alternator kVA loading. A resistive bank proves real-power loading at unity PF; adding inductive kVAR is required when the test must reproduce a lower lagging power factor.

How to use this calculator

Enter the generator nameplate real-power rating in kW.

Enter the power factor the test is intended to reproduce; use 1.0 for a resistive-only test.

Choose the planned load percentage from the approved test procedure.

Enter load-bank terminal voltage and phase.

Select load-bank equipment with adequate kW, kVAR, voltage, current, step resolution and thermal duty; verify the final test procedure with the generator and load-bank manufacturers.

Where people use it

•Sizing resistive capacity for generator exercise and commissioning.
•Estimating inductive kVAR needed to reproduce a generator rated power factor.
•Checking load-bank connection current at the planned test point.
•Separating engine real-power loading from alternator apparent-power/current loading.

Example: 500 kW generator, 0.8 PF, 100% test

A 500 kW test at 0.8 PF is 625 kVA. The corresponding reactive requirement is 375 kVAR. At 480 V three-phase the target-PF line current is about 751.76 A, while a resistive-only 500 kW bank draws about 601.41 A.

Follow the approved test procedure and equipment ratings

•This calculator sizes electrical load capacity; it does not define an acceptance test, test duration, mandatory load steps or pass/fail criteria. Follow the applicable project specification, authority requirements and manufacturer procedure.
•A resistive-only load bank operates at approximately unity power factor. It can fully load engine kW while leaving alternator kVA/current below a lower nameplate PF rating.
•Use the actual voltage at the load bank. Resistive kW changes with applied voltage, and long test cables can introduce voltage drop.
•Confirm load-bank voltage/current ratings, cooling airflow, duty cycle, connection hardware and cable ampacity separately.
•Do not infer generator transient performance, harmonics, leading-PF capability or protection settings from this steady-state sizing result.
•Reactive sizing shown is for a lagging inductive component paired with the entered resistive kW.

Frequently asked questions

What size load bank do I need for a generator?+

For a resistive test, required bank kW is generator rated kW multiplied by the planned test percentage. If the procedure requires rated lagging power factor, also size the inductive kVAR and total kVA/current.

Why is kVAR needed for a 0.8 PF generator test?+

A resistive bank is near PF 1.0. Adding inductive load increases apparent power and current without increasing real kW to the same degree, allowing the alternator to be tested closer to its rated kVA/PF.

How much kVAR corresponds to 0.8 PF?+

At 0.8 PF, kVAR is 0.75 times kW because tan(arccos(0.8)) = 0.75. The calculator uses the general power-triangle equation for any valid entered PF.

Does this tell me the required NFPA or ISO test sequence?+

No. Standards, editions, installation class, project specifications and manufacturer instructions determine required procedures. This tool only performs the electrical sizing math.

Why is load-bank current higher at lower power factor?+

For the same kW, lower PF means higher kVA. Current follows kVA, so a combined resistive/reactive test can require more current than a resistive-only test.

Should I use generator voltage or load-bank terminal voltage?+

Use the actual or expected load-bank terminal voltage for connection-current planning and verify voltage drop. Resistive elements also derate when applied voltage differs from their rating.

Semantic next steps

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