The insertion of the measurement of Partial Discharges done at the same time of the Surge Test – with E.D.C. method – allows to find turn in short also where the standard Surge Test parameters (Inductance and Energy Loss) doesn’t see any variation, as the fault is too small to cause a discharge detectable by standard Surge Test.
In figure 1 it is simulated the partial lack of insulation that can occur in the stator between coils of the same winding or coils of two connected windings. To simulate this kind of fault, we connected a non-insulated wire between a terminal of the stator and another point of the winding. In this way, the insulation is missing from one side only and the defect is only visible with partial discharge measure and not with the surge test, that can identify only complete short-circuits between coils.
The surge curve will not change with the fault simulation, the defect is identified only with partial discharge.