Cummins Power Rating Application Guidelines for Generator Drive Engines

These guidelines have been formulated to ensure the proper application of generator drive engines in A.C. generator set installation. Generator drive engines are not designed for and shall not be used in variable speed D.C. generator set applications.

STANDBY POWER RATING is applicable for supplying emergency power for the duration of the utility power outage. No overload capability is available for this rating. Under no condition is an engine allowed to operate in parallel with the public utility at the standby power rating. This rating should be applied where reliable utility power is available. A standby-rated engine should be sized for a maximum of an 80% average load factor and 200 hours of operation per year. This includes less than 25 hours per year at Standby Power rating. Standby ratings should never be applied except in true emergency power outages. Negotiated power outages contracted with a utility company are not considered an emergency.

CONTINUOUS POWER RATING is applicable for supplying utility power at a constant 100% load factor for an unlimited number of hours per year. No overload capability is available for this rating.

PRIME POWER RATING is applicable for supplying electric power in place of commercially purchased power. Prime Power applications must be in the form of one of the following two categories:

UNLIMITED TIME RUNNING PRIME POWER: Prime Power is available for an unlimited number of hours per year in a variable load application. Variable load should not exceed a 70% average of a period of 250 hours.

The total operating time at 100% Prime Power shall not exceed 500 hours per year.

A 10% overload capability is available for a period of 1 hour within 12 hours of operation. Total operating time at the 10% overload power shall not exceed 25 hours per year.

LIMITED-TIME RUNNING PRIME POWER: Prime Power is available for a limited number of hours in a non-variable load application. It is intended for use in situations where power outages are contracted, such as in utility power curtailment. Engines may be operated in parallel to the public utility for up to 750 hours per year at power levels never to exceed the Prime Power rating. The customer should be aware, however, that the life of any engine will be reduced by this constant high-load operation. For any operation exceeding 750 hours per year, a Prime Power rating should use the Continuous Power rating.

Reference Standards:
BS-5514 and DIN-6271 standards are based on ISO-3046
Operation at Elevated Temperature and Altitude:
The engine may be operated at:
1800 RPM up to 5,000 ft. (1,500m) and 104°F (40°C) without power derating.
For sustained operation above these conditions, derate by 4% per 1,000ft. (300m), and 1% per 10°F (2% per 11°C).