This paper presents the results of an experimental investigation on the harmful effects due to the PWM inverter supply on low voltage induction motors. Laboratory tests have verified on two different models of motors the reflected wave phenomenon, which induces on their terminals a rising voltage edge with peaks higher than twice the DC link voltage; further tests in a qualified firm have revealed that these peaks exceed the partial discharge inception voltage (PDIV) for one of the two types of motor. An invasive and specialized series of tests on the insulation material extracted from the stators has proven that an appropriate insulation system represents the best solution to avoid an early die-off of inverter-fed motors. Other two mitigation methods proposed in the literature have been experimentally tested, revealing that they do not assure the solution to the problem.
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