Nonsustained Breakdowns in Electrical Strength Tests

A study of nonsustained breakdowns has been made during alternating voltage tests on the electric strength of various commercial insulants in transformer oil and compressed sulphur hexafluoride and nitrogen. Such breakdowns do not cause sustained arcing and current flow. It is demonstrated for normal test circuits, that the voltage required for nonsustained breakdown may be significantly below that which will cause a sustained discharge. Experimental results of the effect of test circuit parameters and relay settings on the breakdown voltages recorded are given. The implications of these results on the hitherto accepted practice of ignoring nonsustained breakdowns in many insulation testing standards are discussed, and these might well be taken into consideration when the testing standards are reviewed for possible revision.