Development of test method to verify water induced corona on composite insulator housing

Two main criteria for the optimal design of corona/grading rings for composite insulation system include limit of E-field to avoid corona from a metal part and limit E-field to avoid water-induced corona on composite surface. At present only the first criterion is verified by the standard RIV test. This paper presents an innovative laboratory test method that can be used as a verification of the composite insulation system design to avoid water induced corona on the surface. Several approaches of producing water induced corona have been tested and evaluated. Pre-tests were performed on a small test object to optimize the different procedures. Tests were then performed on a full scale 420 kV composite insulator to verify the complete procedure. Different measuring techniques have also been evaluated. 3D calculation of the electric field for all tested structures has also been performed in Comsol software and compared to E-field criteria. Results from these calculations have also been compared with corona inception levels from the different tests and a good correlation was found. The innovative non-standard Water Drop Corona Induced test seems to be the best practical option for further development.