Influence of defects in windings insulation on its operation reliability

Low-voltage induction motor is one of the most widely used types of electrical machines. Today more and more end users demand reliable and energy efficient electrical machines as an extra feature. Design and applying of control systems for improving energy efficiency must be in correlation with reliability requirements; it is necessary to fetch out the changing operation conditions that can lead to unexpected failures, and to prevent them. This paper describes the influence of insulation defectiveness on winding insulation system reliability in PWM based regulation applications. Currently, the influence of technological defects in the winding insulation on its reliable operation in motor being part of the variable frequency drive has not been thoroughly studied. The relevance of this research is determined by the need to study the “healing” of winding insulation through defects by the impregnation, and its influence on the mean time to failure. The study results will permit to give recommendations for improving the reliability of low voltage windings and subsequently the reliability of induction motors fed by PWM invertors. The study was carried out using a test technique adapted to variable frequency drives and applied to insulation system “varnish - enamelled winding wire”. The experimental results are presented and the main findings are discussed.