Generator Set and UPS Compatibility

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This paper discusses problems that can be encountered in operating UPS equipment on generator set equipment, explains reasons behind some problems, and identifies steps that can be taken to minimize compatibility problems between generator sets and static UPS equipment. There is a "Conventional Wisdom" that a generator set provided for use with a UPS should be sized so that the generator set is always two to five times the capacity of the UPS. One problem with that guideline is that there is no firm consensus in the industry of what exact number to use and little technical basis for a recommendation based on sizing alone. There have been observed cases where SCR loads as small as 3 kW have disrupted operation of a 100kW generator.