Diagnostic technique to assess the condition of stator insulation by measuring microwave associated with dielectric breakdown

Partial Discharge (PD) occurring in the stator insulation of the generator is a symptom and/or a direct cause of the deterioration of the insulation system. It is reported that PD is a very short duration current and/or voltage pulse, about 1/spl sim/5 [ns]. Generally PD emits electromagnetic waves which are broadband signals (/spl sim/GHz). Therefore we developed a new system for detecting the electromagnetic waves, especially microwave (GHz) emitted from. From the point of view of protecting an accident caused by the insulation breakdown, it is important to assess the condition of the winding. We applied our system to a dielectric breakdown test to know the relation between the characteristics of the microwave and the insulation condition of the winding. The dielectric breakdown test is useful for estimating the minimum breakdown voltage which is a criterion of the insulation condition of the winding. Experimental results showed that this system was able to assess the insulation condition by measuring the number of the pulses of the microwave per voltage cycle.