Nonsustained disruptive discharges in vacuum interrupters

Many researchers have studied breakdown phenomena after current interruption of vacuum interrupters (VIs), but only a few made a distinction between breakdowns followed by the flow of the power-frequency current and a high-frequency current flow which is related to (stray) capacitance local to the interrupter. The latter is called a nonsustained disruptive discharge (NSDD) which in fact is now also being recognised by the International Electrotechnical Commission (IEC). Up till now, only the Short-Circuit Testing Liaison (STL) mentioned this phenomenon in its guide used for interpretation of IEC-publication 60056(1987). They interpret the occurrence of a NSDD as showing some signs of distress in the VI and accepted the occurrence of this phenomenon to a maximum of three during an entire series of test duties. In this paper this matter is discussed and looked deeper into detail what is known about NSDDs until today. Well known explanations for this phenomenon are discussed as, e.g., mechanical shocks of the driving mechanism which could release micro-particles from the electrodes or inner walls but also other explanations, which can be found in literature, are addressed. Finally, the practical importance of an occurrence of a NSDDs on the utility grid is discussed