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 inverters could have serious economic impact if it is not addressed. Indeed, even though much already has been written on the different topics related to the use of such power supplies, there is a great need for a better understanding of the physical mechanisms involved, particularly with regards to aging mechanisms of insulating materials. The aim of this paper is to highlight the effect of adjustable speed drives (ASD) on the stator winding insulating materials. Pulse-like electrical stresses have been applied to three types of samples (thin him, twisted pair, and layer to layer). Physical characterization and/or lifetime measurements have been performed. The results are presented and discussed according to the nature of the interaction existing between the electrical stress main characteristics (magnitude, frequency, dV/dt) and the material properties. According to these results, the development of a standardized insulation quality control test, based on a physical understanding of involved stresses and material behavior, appears now to be necessary.