Temperature Dependence of RPDIV of Motorette Sample with Varnish Treatment

Recently, driving of inverters has been advanced to improve the characteristics of motors. Along with that, concerns are raised that inverter surge deteriorates the insulation system of the motor. The problem of insulation deterioration is particularly serious in high-voltage motors where insulation structure is important, and analysis of phenomena of deterioration is strongly desired. We have measured repetitive partial discharge inception voltage (RPDIV) of an enamel twisted pair sample using a repetitive impulse voltage generator which can arbitrarily change the voltage value, pulse rise time and width, etc. This paper deals with RPDIV of a motorette that can simulate all connections in the motor (phase to phase, turn to turn, phase to ground) and investigates the influence of temperature on RPDIV characteristics. Measurements of RPDIV of the motorette with varnish treatment were also made in the temperature range between room temperature 25°C and 155°C. Experimental results revealed that the RPDIV for the phase to phase and turn to turn connection tends to decrease with increase in temperature. An attempt is made to interpret the temperature dependence of the RPDIV in terms of the temperature dependent pressure change in void defect which may exist in the vanish of the motorette.