Small wind / Buyer questions
Electrical configuration
Why are generator, DC-bus and grid currents different?
The short answer
The circuits can have different voltages, waveforms, phase arrangements and power factors. Power conversion changes those relationships, and losses also separate input from output. A current value from the generator therefore cannot simply be copied onto the DC circuit or final AC connection. Every current rating in a quotation should identify its measurement point, whether it is RMS or another quantity, and its permitted duration.
An equal-power example with different currents
Hypothetical loss-free comparison: 4 kW at a 200 V DC boundary corresponds to 20 A. At a 400 V balanced three-phase AC boundary with unity power factor, 4 kW corresponds to approximately 5.8 A line current. At 230 V single phase and unity power factor, it corresponds to about 17.4 A.
The different currents are consistent with the same active-power value because the circuit definitions differ. Real converters add losses and may have reactive or distorted currents.
Ask which rating is being quoted
| Current label | Useful accompanying information |
|---|---|
| Generator current | Speed/load condition, phase and waveform definition |
| DC current | DC voltage range, average/ripple distinction and direction |
| AC output current | Voltage, phase arrangement, power factor and RMS definition |
Continuous, transient and fault-related values should not be treated as interchangeable.
Use current correctly when comparing components
A controller's “100 A” label is incomplete without the circuit boundary and operating range. The same is true of a converter's AC limit or a meter's reading. Apparent agreement on amperes can conceal a mismatch in voltage, duty or measurement method.
Use the single-line diagram to attach each value to its circuit. Final conductors, protection and installation details require the actual equipment data and the qualified designer's assessment.
Record the direction as well as the magnitude
An energy-storage or hybrid interface may carry power in more than one direction during different modes. A positive current on one device can mean charging, while another device uses the opposite sign convention. Define the direction on the diagram and in the monitoring map before comparing readings or interpreting an unexpected negative value.
Sources
- Schneider Electric: single- and three-phase power calculations
- U.S. DOE Energy Management for Motor-Driven Systems
Examples are illustrative. Confirm product-specific performance, compatibility and supply scope in the applicable documents.