Abstract
Various nondestructive and breakdown tests were conducted with the two types of traction motors of electric locomotives of JNR which had been in service for many years. This paper describes nondestructive and breakdown characteristics. As the insulation resistance and tan δ are subject to environmental conditions such as humidity and temperature, we should be very careful to prevent their effect. On the other hand, the partial discharge characteristics are relatively little affected by the surrounding, also a considerable correlation is observed among the partial discharge characteristics and the breakdown voltage. This leads to the possibility of degradation judgement to a certain extent by the nondestructive test. The authors proposed the following guidelines for judging insulation detrioration in the partial discharge characteristics when the partial discharge measuring instruments are applied to an insulation test of relatively low voltage electric motor. (1) Partial discharge inception voltage (Vi): More than 1kV. Only for armature winding, more than 1.5kV. The windings which exhibit these test data have necessary insulation strength for operation. (2) Maximum partial discharge magnitude (Qmax): Below 10×10-9 coulomb. Only for armature winding, below 2×10-9 coulomb. The windings which exhibit these test data have necessary insulation strength for operation. (3) Partial discharge current(I): Below 3×104× 10-9A. Only for commutating pole winding, below 2×104×10-9A. The windings which exhibit these test data have necessary insulation strength for operation.
