Thermal performance of stress grading systems for converter-fed motors

2009 IEEE Electrical Insulation Conference

2009

The paper addresses the anisotropic dielectric properties of composite dielectric materials used in the stress relief of medium voltage form-wound motor coils. Experimental results and a comprehensive coupled electro-thermal model of a form-wound coil subjected to repetitive fast pulses are presented. The study also introduces an alternative method to examine the thermal effects of repetitive fast pulses in the stress relief, using two sinusoidal waveforms with pre-selected frequencies and amplitudes.

Section: Materials Characteristicsmentioning

confidence: 99%

Anisotropic dielectric properties of stress grading materials used in medium voltage form-wound motor coils to study thermal effects of repetitive fast pulses

2009 IEEE Electrical Insulation Conference

2009

“…Under such circumstances, hotspots are developed in the coils due to joule heating and dielectric losses corresponding to fast pulses and high repetition rates. These hotspots can deteriorate the coil insulation, eventually leading to motor failure [1][2][3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Analysis of thermal stresses in medium voltage motor coils under repetitive fast pulses

2009 IEEE Conference on Electrical Insulation and Dielectric Phenomena

2009

The paper discusses the thermal stresses on medium voltage form-wound motor coils due to repetitive impulse and square-wave voltages. Based on the frequency spectra of such pulse trains, and their corresponding signal powers, it is proposed that a set of sinusoidal high frequency voltages of determined amplitudes can effectively produce similar thermal stresses. Both the experimental and simulation results are in agreement with the above proposed scheme.

“…In addition, for an actual multidielectric insulation system such as form-wound machine insulation, the dielectric materials, particularly the SGT and the CAT, have dielectric parameters that are normally dependent on frequency, electric field, and temperature. In other words, for each harmonic and in each subsystem, the appropriate dielectric parameters regarding the system geometry must be found and used in equation (4). This constraint gives rise to an impractical approach to calculating the electrical loss and to overcome this problem, a novel approach is proposed.…”

Section: Signal Powermentioning

confidence: 99%

“…This type of complex voltage waveform, for example, pulse width modulated (PWM) voltage, may increase the dielectric heating in the stress grading tape (SGT) and the conductive armor tape (CAT) in the insulation system. The surface heating may produce localized hot spots in these tapes that can cause the coil groundwall insulation to deteriorate, eventually leading to motor failure [1][2][3][4][5].…”

Section: Introductionmentioning

confidence: 99%

Analysis of thermal stresses in medium-voltage motor coils under repetitive fast pulse and high-frequency voltages

IEEE Trans. Dielect. Electr. Insul.

2010

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.Index Terms -Nonlinear field dependent stress grading, conductive armor tape, thermal stress, PWM and square wave voltage, coupled electro-thermal FEM modeling.Emad Sharifi (S'08) received the B.Sc. degree from Isfahan University of Technology in 1991 and the M.Sc. degree from K. N. Toosi University of Technology, Tehran, Iran, in 1994, both in electrical engineering. He worked for 12 years in the MATN Company and Niroo Research Institute (NRI), Tehran, Iran. He is currently working toward the Ph.D. degree at the University of Waterloo, Ontario, Canada. His current research interests include the grading of electric fields under power frequencies and repetitive fast pulses, dielectric characteristics at high frequencies and high electric field, and electro-thermal FEM modeling of electric machine and cable insulations. Shesha Jayaram (M'