Why the rating matters
A generator can be advertised with different output figures depending on its duty rating. Prime and standby ratings describe different operating conditions and limits. A larger standby figure does not mean the set can deliver that output continuously.
Prime power
Prime ratings are intended for supplying a varying electrical load under the manufacturer’s defined operating conditions. Permitted loading, maintenance requirements and any overload capability must be checked in the documentation for the specific generating set. Do not assume that every prime-rated generator has the same operating allowance.
Standby power
A standby rating is intended for emergency supply when the normal power source is unavailable, subject to the manufacturer’s loading and operating-hour limits. A used standby generator may have low hours, but its maintenance history, condition and test results remain important.
kVA and kW
kVA expresses apparent power; kW expresses real power. For a stated power factor, kW = kVA × power factor. At a power factor of 0.8, 100 kVA corresponds to 80 kW and 500 kVA corresponds to 400 kW. These calculations describe the relationship between the units; they do not establish the available prime or standby rating of an unidentified generator.
What to check on a used set
- Prime and standby outputs on the generator nameplate.
- Voltage, phase, frequency and power factor.
- Manufacturer limits for loading and annual operating hours.
- Site altitude, ambient temperature and cooling arrangement.
- The effect of motor starting, nonlinear loads and load steps.
Send UGT your intended operating pattern and load list. We can discuss available stock and obtain the specification needed to assess a particular set.
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