What is kVA?
kVA stands for kilovolt-amperes. It represents the apparent power of a generator: the total electrical power available before accounting for how a load uses it.
Generators are rated in kVA because they must supply both:
- Real Power (kW) – the usable power that performs work
- Reactive Power (kVAr) – power demanded by inductive loads (motors, pumps, compressors)
kVA vs kW – What’s the Difference?
The relationship depends on power factor (PF):
Formula:
kW = kVA × Power Factor
In the UK, many generator ratings use a standard PF of 0.8.
| Generator Size (kVA) | Power Factor | Usable Power (kW) |
|---|---|---|
| 100 kVA | 0.8 | 80 kW |
| 200 kVA | 0.8 | 160 kW |
| 500 kVA | 0.8 | 400 kW |
Why Power Factor Matters
Power factor reflects how efficiently electrical power is used. Inductive loads like motors reduce PF, which means more kVA is needed to deliver the same kW output.
That’s why correct generator sizing is important for industrial and agricultural sites, especially where motor starting (inrush) is involved.
Prime vs Standby kVA Ratings
- Standby: for mains failure backup; typically no overload capability
- Prime: for regular use; often allows limited overload (manufacturer dependent)
