Temperature and electric field dependence of stress grading on form-wound motor coils

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.

[1]  S. Boggs,et al.  Engineering with nonlinear dielectrics , 2004, IEEE Electrical Insulation Magazine.

[2]  E.A. Cherney,et al.  Capacitive Grading of 13.8 kV Form-Wound Motor Coil Ends for Pulse Width Modulated Drive Operation , 2008, Conference Record of the 2008 IEEE International Symposium on Electrical Insulation.

[3]  Nathaniel Taylor.  Diagnostics of stator insulatin by dielectric response and variable frequency partial discharge measurements : a study of varied low frequencies in stator insulation, with particular attention to end-winding stress-grading , 2006 .

[4]  H. El-Kishky,et al.  Time-domain analysis of nonlinear stress-grading systems for high voltage rotating machines , 2003, 2003 Annual Report Conference on Electrical Insulation and Dielectric Phenomena.

[5]  J.C.G. Wheeler,et al.  Finite element modelling of nonlinear stress grading materials for machine end windings , 2002 .

[6]  F.P. Espino-Cortes,et al.  Impact of inverter drives employing fast-switching devices on form-wound AC machine stator coil stress grading , 2007, IEEE Electrical Insulation Magazine.

[7]  J.C.G. Wheeler,et al.  Novel stress grading systems for converter-fed motors , 2007, IEEE Electrical Insulation Magazine.

[8]  G. Stone,et al.  Electrical Insulation for Rotating Machines , 2003 .

[9]  F. T. Emery.  The application of conductive and stress grading tapes to vacuum pressure impregnated, high voltage stator coils , 1996 .

[10]  Shesha H. Jayaram,et al.  Anisotropic dielectric properties of stress grading materials used in medium voltage form-wound motor coils to study thermal effects of repetitive fast pulses , 2009, 2009 IEEE Electrical Insulation Conference.