Capacitively Graded Oil-Paper Insulation Behavior Under Repeated Flashover Conditions

In order to ensure the withstand capability of the high voltage apparatus against high-frequency transients, multiple chopped impulse test is usually defined. Such tests serve as a basis of replicating in-field phenomena produced by the operation of switching devices located in the vicinity of the apparatus. However, the testing procedure methodology proposed within the IEC/IEEE standards may not simulate the severity of actual effects in an adequate way. This work presents a novel approach in simulating such transient voltage stresses in the laboratory and gives insight on improving the standard testing procedures. Simplified insulation models are tested using the presented approach and standard diagnostic measurements are done on the models to investigate the insulation behavior during testing. The results show that mentioned high voltage transients' effect on insulation, occurring during the disconnector pre-strikes or re-strikes, can be provoked by the given testing approach.