Prime and Standby Generator Ratings Explained
A set advertised at 1000 kVA and a set advertised at 900 kVA can be the same machine. The difference is which rating is being quoted.
Two Numbers For One Machine
The prime rating is the output a set can supply continuously in normal service. The standby rating is the higher output available for emergency use when the mains supply fails, and it is not intended for continuous running. Cummins generator engines in this catalogue list both where the source data sheet gives them, for example a prime power of 80 kW with a standby power of 90 kW.
Speed Fixes The Frequency
Generator-drive engines run at 1500 rpm for 50 Hz supply and at 1800 rpm for 60 Hz. The rated speed on each product page tells you which market the unit is built for, and a set can be built for either frequency if it is specified with the order.
Size Against The Real Load
Size the set on the connected load and its starting characteristics, not on the headline kVA. Motor starting, transformer inrush and non-linear loads all draw more than their nameplate current for a short time, which is why a set that looks generous on paper can stall on block load.
MEP Power supplies packaged Cummins sets from 30 kVA to 3000 kVA. Send the connected load, the duty and the frequency required and the range is matched to the application.
Models Mentioned In This Guide
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