Development of a type test for turn insulation in motor coils

Work done to develop a type test for turn insulation in form-wound multiturn motor coils is discussed. A concept for accelerated aging of turn insulation by applying thermal stress and electrical stress across the groundwall and the turn insulation simultaneously was developed and verified in preliminary tests on a few single coils. In the accelerated aging experiment, four to six coils were aged simultaneously. Turn insulation was aged for 500 h in ten coils and for 1000 h in twelve coils. The impulse breakdown voltages were measured for the aged and the unaged coils for comparison. Thus a type test to check the quality of turn insulation was developed. However, more tests on many more coils of different insulation design are required to establish the efficacy of the type test. The problems encountered in the tests are described, and plans for ongoing work in this area are outlined