Adequacy of rotating machine turn insulation testing

In the past few years, Ontario Hydro has experienced a number of turn insulation failures in large motors in nuclear and fossil plants. Furthermore, one of the primary reasons for replacing stator windings in older hydraulic generators is the loss of turn insulation integrity. That is, the turn insulation condition often determines the end-of-life of a winding. This paper reviews the adequacy of published testing methods both for qualifying turn insulation systems and for quality control. From a utility's point of view, there appears to be a need for more rigorous "type' and "quality control' tests, equivalent to those now required for groundwall insulation.