A coupled electro-thermal study of the stress grading system of medium voltage motor coils when energized by repetitive fast pulses

The paper discusses the temperature profile along the stress grading and the conductive armor layers on the endwinding of a 13.8 kV motor coil when energized by repetitive fast pulse voltages such as pulse width modulated (PWM) voltages. The effect of the pulse rise time in the temperature profile at the end portion of the motor bar is also measured experimentally. The thermal stress due to two equivalent high frequency sinusoidal voltages is analyzed using 3D FEM coupled electrical and thermal modeling.