Testing of low-voltage motor turn insulation intended for pulse-width modulated applications

The problem of premature failure of low voltage rotating machines fed by in verters could have serious economic impact if it is not addressed. Indeed, even though much already has been written on the different topics related t o the use of such power supplies, there is a great need for a better unders tanding of the physical mechanisms involved, particularly with regards to a ging mechanisms of insulating materials. The aim of this paper is to highli ght the effect of adjustable speed drives (ASD) on the stator winding insul ating materials. Pulse-like electrical stresses have been applied to three types of samples (thin him, twisted pair, and layer to layer). Physical cha racterization and/or lifetime measurements have been performed. The results are presented and discussed according to the nature of the interaction exi sting between the electrical stress main characteristics (magnitude, freque ncy, dV/dt) and the material properties. According to these results, the de velopment of a standardized insulation quality control test, based on a phy sical understanding of involved stresses and material behavior, appears now to be necessary.