Electric Power Principles, 2nd Edition

8Electromagnetic Forces and Loss Mechanisms

This chapter reviews some of the fundamental processes involved in electric machinery. Motors and generators convert electrical power to and from mechanical form, and to understand how they work one must understand the basics of electromechanical energy conversion. In the section on energy conversion processes we examine two fundamental ways of estimating electromagnetic forces: those involving thermodynamic arguments (conservation of energy) and field methods (Maxwell's stress tensor and Poynting's theorem) are considered here.

This is a brief review of the fundamentals of electromechanical energy conversion. A more thorough explication of this area can be found in the three‐volume set Electromechanical Dynamics (Woodson and Melcher 1968).

This chapter also discusses losses resulting from eddy currents in both linear and nonlinear materials and hysteresis, including development of semi‐empirical ways of handling iron losses that are combinations of eddy currents and hysteresis.

8.1 Energy Conversion Process

In a motor or electrical actuator, the energy conversion process can be thought of in simple terms. Electric power input to the machine is just the sum of electric power inputs to the different phase terminals:

Mechanical power output is torque multiplied by speed:

and the sum of the losses is the difference:

It will sometimes ...