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The paper addresses the ac modeling and anisotropic dielectric properties of stress grading and conductive armor tapes that are two crucial components in form-wound motor coils. The limitations of the conventional dc conductivity modeling and the necessities of using ac conductivity modeling and anisotropic properties of these materials at high frequencies and high electric field are discussed. The method of measurement of the dielectric parameters at high frequency and high electric field for 2D modeling is also presented. The transient FEM simulations from conventional modeling and the proposed ac modeling are compared to experimentally obtained results. Good agreement is only obtained from the latter modeling. [ABSTRACT FROM AUTHOR]

The paper addresses the temperature and electric field dependence on the conductivity of the conductive armor and stress grading tapes on form-wound motor coils. The temperature and electric field dependence is measured in the laboratory, and the nonlinear dependency is used in transient FEM simulations of the potential distribution on the form-wound coils. The surface potential distribution, for various temperatures and applied voltages, is measured in the laboratory from which the surface electric stress is calculated. Good agreement between the simulated and measured stresses is obtained. A temperature of 155 °C is shown to have little influence on the stress grading, but the electric stress dependence on conductivity is shown to have a major influence on the stress grading of the motor coil examined in this study. [ABSTRACT FROM AUTHOR]

The paper provides an analysis of the thermal stresses in medium-voltage form-wound motor coils that arise from pulsed width modulated, repetitive square-wave, and impulse voltages. The effects of the shape, repetition rate, and rise and fall time of the pulses are studied through experimental and computational work. Based on the frequency spectra of the pulse trains and their corresponding signal powers, it is shown that a set of sinusoidal high-frequency voltages of predetermined amplitudes can effectively produce consistent thermal stresses, and both the experimental and simulation results confirm the validity of the proposed scheme. [ABSTRACT FROM PUBLISHER]