Insulation Diagnostic Technique to Assess the Condition of Generator Winding by Measuring Microwave Associated with Dielectric Breakdown

Partial Discharge (PD) occurring in the insulation of the stator winding of the generator is a symptom of the deterioration of the insulation system. PD is a very short duration current and/or voltage pulse, about 1-5 ns. Generally PD emits broad band electromagnetic wave (~ GHz). We developed a new system for detecting the microwave emitted from PD. From the point of view of predicting an accident caused by the insulation breakdown of the generator winding, 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 condition of the insulation system 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 microwave frequency per voltage cycle.