UPS Battery constraints
The battery must enable continued operation over a time that is not:
UPS batteries have standard backup times of five to ten minutes, at a very reasonable cost in terms of installation and operation.
Diesel Generator constraints
A Diesel Generator must operate a minimum amount of time (at least 15 minutes) to avoid excessive wear, it must be started only when necessary. A normal Diesel Generator requires approximately two minutes to start and ramp up to the point where the temperature is stable.
This process includes the following:
• the diesel engine driving the generator must start and reach its rated speed (eight to ten seconds),
• The motor and the generator must ramp up to full power (12 to 15 seconds),
• A Diesel Generator may not start on the first try and may stall during the ramp-up period
A Diesel Generator combined with a UPS must not start until approximately three minutes after utility power has been lost:
• to provide the distribution-system automatic devices (reclosers, etc.) with the time required to restore power, if possible,
• to avoid frequent and unnecessary starting of the Diesel Generator
Our Conclusion and Suggestion
A backup power protection system providing ten minutes is well suited to Diesel Generators. It corresponds to a cost-effective, standard solution that ensures optimum use of the battery itself and the Diesel Generator.
A ten-minute backup time provides: