Small wind / Buyer questions
Electrical configuration
Does a 10 kW wind inverter also need a kVA rating?
The short answer
Yes, the apparent-power or current capability can matter alongside real power. kW describes active power; kVA describes apparent power. Power factor relates the two at the specified AC boundary. A converter advertised for a certain kW output may have separate constraints on current, reactive-power operation and temperature. Its turbine power label cannot replace the converter's actual capability information.
Use the relationship at the correct boundary
Illustrative sinusoidal-load calculation: a load using 8 kW at a power factor of 0.8 requires 10 kVA. At unity power factor, 8 kW corresponds to 8 kVA. These are different apparent-power demands for the same useful active-power consumption.
Do not apply a load's assumed power factor blindly to the generator side or to every operating mode. Non-sinusoidal current and manufacturer capability limits require their own treatment.
Read a proposal in four dimensions
| Quantity | What it helps check |
|---|---|
| kW | Active-power conversion or supply |
| kVA/current | AC current capability at the stated voltage |
| Reactive-power capability | Permitted operating combinations |
| Duration and temperature | Whether the stated capability is continuous |
A short surge rating and a continuous rating serve different purposes and should remain separate in the comparison.
Grid export and islanded loads are different duties
A grid-connected converter may have an operator-specified reactive-power duty. An off-grid inverter must also serve the actual load characteristics and starting events. Their useful comparison therefore extends beyond whether both cabinets display “10 kW.”
Request the capability information applicable to the proposed package and operating mode. The example above explains the units; it does not establish MARSTON converter ratings, grid functions or motor-starting capability.
Identify which limit binds first
When comparing proposals, ask whether active power, apparent power, current or temperature restricts the intended operating point first. A converter with enough nominal kW may still be unable to provide that active power alongside the requested reactive duty. The permitted combination should come from the actual equipment capability information, not from independent maximum labels added together.
Sources
- U.S. DOE Energy Management for Motor-Driven Systems
- Schneider Electric: single- and three-phase power calculations
Examples are illustrative. Confirm product-specific performance, compatibility and supply scope in the applicable documents.