Two figures describe different things
Kilowatts (kW) describe real power: the rate at which electrical energy performs useful work. Kilovolt-amperes (kVA) describe apparent power. Power factor relates real power to apparent power for the same electrical condition.
The relationship is:
kW = kVA × PF
kVA = kW ÷ PF
Use quantities that describe the same load condition. A rating on the generator data sheet and the actual power factor of your connected load are not automatically the same.
A worked conversion
If a load requires 100 kW at a power factor of 0.8, its apparent power is 125 kVA. This is a mathematical illustration with stated assumptions. It does not mean that a 125 kVA generator will meet every requirement of that load.
| Stated input | Calculation | Result |
|---|---|---|
| 100 kW, PF 0.8 | 100 ÷ 0.8 | 125 kVA |
| 100 kVA, PF 0.8 | 100 × 0.8 | 80 kW |
Use the editable converter to check a value with your own power factor.
Why this is not a sizing method
Generator selection must also consider engine real-power capability, alternator capability, starting loads, allowable voltage and frequency changes, and site conditions. Loads with electronic drives or non-linear characteristics may need additional review.
A simplified conversion does not describe motor starting or the way loads change over time. Sending only a total kVA figure can hide information the supplier needs.
Questions to put on the enquiry
Ask which power factor is associated with the stated rating, which duty rating applies, and which ambient conditions were used. Supply the actual load schedule wherever possible. Have an application engineer review the proposed set against that schedule before ordering.
Sources & scope
- Cummins — T-030 Generator Set Application Manual · §3.3.4.2 Power factor and the relationship between kW and kVA. Issue 9, February 2015; not represented as the latest edition.
- Generator Source — Power Calculators Additional reference for kW/kVA calculations. A conversion alone does not validate generator selection.
General procurement guidance. Worked examples are illustrative; final selection requires the selected manufacturer's documentation and a project-specific engineering review.