Multifactor aging of electrical machines energized by standard PWM drives

The effects of pulse width modulated drives on the life of motor insulation are studied by researchers from various segments of the electrical machinery industry. Insulation materials manufacturers are introducing new products resistant to the before mentioned effects. Motor manufacturers are designing insulation systems that will use the synergy of new materials. Drive manufacturers are advising filters and different drive topologies as counter measures against harmful effects of high voltage, high speed pulses. Here at Emerson Electric, we are comparing the results of the initial tests on twisted wire pairs with the life test data of actual motors energized by standard industrial drives. A particular construction of the insulation system used in the electrical machine is showing a definitive difference in the resulting life of the motor. The machines with and without phase paper, using standard magnet wire, are contrasted with the machines using the new type of PWM resistant magnet wire. The harmful effects of turn to turn failures are then analyzed using a finite element analysis of possible failure modes in the random wound machines. An analysis of the results obtained by different test methods is presented. Problems in defining the acceptable test characteristics usable in projection of machine life are currently being analyzed. The purpose of this paper is to describe test equipment procedures and experiments related to the development of standardized methods to evaluate insulation materials when subjected to multifactor stresses, such as those imposed by PWM inverters.