IEEE 86-1987 ✓ Most Recent [ Withdrawn ]

Since rotating electrical machines convert mechanical energy to electrical energy, or electrical energy to mechanical energy, base values for each kind of energy appear desirable in formulating a per-unit system. However, the relationship between these energies involves power factor and efficiency, which are not fundamental quantities and which vary considerably between different designs. Traditionally, designers of generators considered rated apparent output power as base power, and designers of synchronous motors considered rated apparent input power as base power. Designers of synchronous motors used rated apparent input power as the base even though it was necessary to estimate efficiency. This permitted the use of the same design equations for both synchronous generators and synchronous motors. Designers of induction motors generally have used rated output power as base apparent power, eliminating assumptions of power factor and efficiency. This was particularly desirable when working with small machines or machines with many poles, where accurate estimates of power factor and efficiency were difficult to make. However, some induction machines are used as induction generators, so that the definitions of input power and output power depend on the mode of operation.