Generator Sizing
Enter the running load, power factor and motors to start and I compute the generator capacity (kVA) with margin, the starting peak and the altitude/temperature derate.
Calculation breakdown
| Item | Value | Detail |
|---|
How it is computed · running, starting and derate
1. Running load in kVA:
kVA_run = kW / PF.
2. Recommended with margin:
kVA_rec = kVA_run × (1 + margin).
3. Starting peak of the largest motor:
kVA_start = (kW_motor / PF) × factor
(DOL 6×, Y-Δ 3×, soft starter 2×). The generator must cover
max(kVA_rec, kVA_start).
4. Site derate: altitude above 1000 m
−3.5 % / 300 m; temperature above 40 °C
−2 % / 5 °C. Combined factor
f = (1 − d_alt) × (1 − d_temp).
5. Required nominal:
kVA_nominal = kVA_rec / f.
! This is an estimate. The starting peak is transient (seconds) and depends on the load torque; check the manufacturer's voltage-dip curve and the motor type. Validate the real PF and expected growth before you buy.
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