Two independent generator-sizing checks — steady running capacity and motor-starting voltage dip — with running load turning out to be the larger, governing requirement in this case.
| Linear (steady) load | 300 kW at 0.85 power factor |
| Non-linear load | 100 kVA, with a 1.5x non-linear derating factor |
| Largest motor starting load | 240 kVA starting kVA |
| Generator subtransient reactance (Xd'') | 0.15 p.u. |
| Maximum acceptable voltage dip | 15% |
| Requirement | Size needed | Governs? |
|---|---|---|
| Running load | 502.9 kVA | Yes — larger of the two |
| Motor-starting dip | 240 kVA | No |
Using the conventional 0.8 power factor genset rating basis.
| Check | Requirement | Actual | Status |
|---|---|---|---|
| Governing sizing requirement | n/a (this is the finding) | Running load (502.9 kVA) exceeds motor-starting requirement (240 kVA) | ✓ PASS |
| Recommended generator size | n/a (this is the result) | 502.9 kVA | ✓ PASS |
Key insight: Which requirement governs generator sizing depends entirely on the ratio between total connected load and the largest single starting load — a site with modest continuous load but one large motor often has starting dip as the governing constraint, while a site with substantial baseline load (like this one, with 300 kW linear plus derated non-linear load) more often finds running capacity is what actually drives the sizing decision. Always compute both, since assuming one governs without checking can lead to an undersized unit.
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Open Generator & Transformer Analysis calculator →Non-linear loads (VFDs, UPS input rectifiers, switch-mode supplies) draw distorted, harmonic-rich current that a generator's alternator has to handle less efficiently than the equivalent linear kVA — the derating factor accounts for the generator needing extra headroom to serve the same nameplate kVA of non-linear load without overheating or excessive voltage distortion, a widely used sizing practice from generator application guides.
A larger single motor relative to total site load — for example, the same generator serving a lighter 100 kW linear/non-linear baseline but starting the same 240 kVA motor would find dipReqKva (still 240 kVA, since it only depends on the motor and generator reactance) now exceeds a much smaller running-load requirement, flipping which check governs the final size.