8: Electromagnetic forces and loss mechanisms
- Page ID
- 54446
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Introduction
This section of notes discusses some of the fundamental processes involved in electric machinery. In the section on energy conversion processes we examine the two major ways of estimating electromagnetic forces: those involving thermodynamic arguments (conservation of energy) and field methods (Maxwell’s Stress Tensor). In between these two explications is a bit of description of electric machinery, primarily there to motivate the description of field based force calculating methods.
The subsection of the notes dealing with losses is really about eddy currents in both linear and nonlinear materials and about semi-empirical ways of handling iron losses and exciting currents in machines.
- 8.1: Energy Conversion Process-
- In a motor the energy conversion process can be thought of in simple terms. In “steady state”, electric power input to the machine is just the sum of electric power inputs to the different phase terminals:
- 8.2: Tying the MST and Poynting Approaches Together
- Now that the stage is set, consider energy flow and force transfer in a narrow region of space as illustrated by Figure 5.
- 8.3: Simple Description of a Linear Induction Motor
- The stage is now set for an almost trivial description of a linear induction motor. Consider the geometry described in Figure 6. Shown here is only the relative motion gap region.
- 8.4: Surface Impedance of Uniform Conductors
- The objective of this section is to describe the calculation of the surface impedance presented by a layer of conductive material. Two problems are considered here.
- 8.5: Iron
- Electric machines employ ferromagnetic materials to carry magnetic flux from and to appropriate places within the machine. Such materials have properties which are interesting, useful and problematical, and the designers of electric machines must deal with this stuff.
- 8.6: Semi-Empirical Method of Handling Iron Loss
- Neither of the models described so far are fully satisfactory in describing the behavior of laminated iron, because losses are a combination of eddy current and hysteresis losses. The rather simple model employed for eddy currents is precise because of its assumption of abrupt saturation.