Failure Mechanism of Stator Windings under Thermal Cycling

Abstract

The purpose of this study was to clarify the mechanism of the thermal deformation and stress build-up of stator windings as well as their failure mechanism under thermal cycling. In this study, the thermal elongation of stator windings was measured over a wide range of temperature variations. By comparing the experimental results with the theoretical ones, the mechanism of thermal deformation and stress build-up was discussed. Thermal cycling tests were also carried out on six kinds of stator windings to clarify the failure mechanism of the stator windings under thermal cycling. In this test, the failure was detected by measuring the flatwise thickness and the tangent delta characteristics of the stator windings. Moreover, the breakdown voltage characteristics were measured at the last stage of the test. The failure mechanism of the stator windings was discussed in conjunction with thermal stress.
From this study, tape separation, mica slipping-out phenomena and bonding failure in mica splitting were revealed. Moreover, the relationship between the mechanical failures described above and the tangent delta and breakdown voltage characteristics was clarified.