The nature of A. C. machine torques

The generation of torque in A.C. machines is not well understood by engineers. National and international standards define only average steady state values and do not cover transient or oscillatory components. The only transient data routinely provided by the manufacturer is short circuit torques. This situation leaves the application engineer in a poor position to properly apply motors or generators. The user needs the complete torque picture. It is the purpose of this paper to present easily usable formulas and a physical picture of torque generation by A.C. machines and thereby fill this long standing need. This paper should eliminate the need for new standards as has been proposed since the data for torque calculation is normally available. Practical and interesting cases will be explored to develop a clear understanding of the nature of A.C. machine torques and their calculation. Torque is a basic physical quantity that can be treated independently and not as a dependent function of power and energy. Each element of a winding under transient as well as steady state conditions contributes a value of torque that is the triple vector product of the radius, the current, and the flux density T^-= R^-r×(I^-×B^-). This wholly empirical formula is firmly established as Langsdorf explains it is the basis for the work that follows.