IEEE 86-1987

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.



Revision Standard - Inactive-Withdrawn. "The proper selection of base values is fundamental to the usefulness of a per-unit system. Although per-unit quantities have been used for many years by designers of rotating machinery, the base quantities were not standardized, and it was necessary to define them in each publication. A working group of the Rotating Machinery Committee was created to propose a set of standard definitions. In 1961, a proposed standard was published for trial use. A critical review of that proposed standard resulted in ANSI/IEEE Std 86-1975. Recently, systems analysts and some designers of rotating electrical machinery have found it useful to have a single generic model for all types of machines. Therefore, alternate per-unit definitions, using input voltamperes as base power for induction motors, have been included in this new revision, as well as an example of an induction generator."