Evaluation of A.C. motor insulation systems by IEEE 117: Water immersion or 100% RH as the conditioning cycle?

The Insulation Research and Development Laboratory of GEC Machines Ltd., Rugby, has had experience of motorette testing for twenty five years and during this time the critical nature of the humidity cycle, taken in conjunction with inadequate precision in the specification of this conditioning cycle, has become apparent. Merely increasing this precision increases practical difficulties and even the present suggested specialised humidity chamber is expensive. As an alternative conditioning cycle, it is proposed that a simple, low cost, water immersion procedure be adopted. Such a procedure has been standard within GEC Machines for the past eight years. The experience gained with this technique is described and performance data for a number of insulation systems are presented. Additional data for the normal 100% RH conditional cycle are given together with some directly comparative data involving the use of the two procedures with identical systems. Full details of the water immersion conditioning procedure are described.