customer's equipment.

Generators operated by low-speed reciprocating engines produce lower frequencies, for a given number of poles, than those operated by, for example, a high-speed steam turbine. For very low prime mover speeds, it would be costly to build a generator with enough poles to provide a high AC frequency. As well, synchronizing two generators to the same speed was found to be easier at lower speeds. While belt drives were common as a way to increase speed of slow engines, in very large ratings