IEEE 86-1975

Since rotating machines convert mechanical energy to electrical energy, or electrical energy to mechanical energy, base values for each kind of energy appear desirable. However, the relationships between these energies involve power factor and efficiency. These are not fundamental quantities, and vary considerably between different designs. While generator designers consider base power to be output power, synchronous-motor designers consider base power to be input power. Other motor designers consider it to be output power. The consensus of large synchronous motor designers favors using the rated apparent input power as the base even though it is necessary to know power factor and efficiency. This permits the use of the same design equations for both synchronous generators and synchronous motors. For induction motors, however, a more practical approach is to use the rated output power as a base, thereby eliminating assumptions of power factor and efficiency. This is particularly desirable when dealing with small machines or machines with many poles, where power factor and efficiency are not known and accurate estimates are difficult to make