Effect of Repetitive Square Voltage on Conventional Stress Grading System

An inverter-fed motor operating above 6 kV driven by the pulse width modulation (PWM) voltage will experience severe electrical and thermal stress. Thus, it is important for insulation designers to study the temperature rise and potential distribution of conventional stress grading system, which comprises main wall insulation, conductive armor tape (CAT) and stress grading tape (SGT) under the repetitive square voltage. Here, two types of stress grading system are designed and optimized, and several experiments and simulations are performed. The rise time of the repetitive square voltage is found to have a significant impact on the temperature rise of the stress grading system. With an increase in dv/dt, the temperature rise of the stress grading system also increases. The capacitive reactance of the main wall insulation decreases, thereby increasing the power loss of the CAT and SGT. Further, an increase in the frequency leads to an increase in the power loss of the stress grading system, and the lower the surface resistance, the lower is the temperature rise. The results of the simulation model are found to be in good agreement with the experimental results, thus verifying the design of the stress grading system. The results of this study are expected to provide an experimental and theoretical basis for the design of stress grading system operating under PWM voltage.