Estimation of vacuum-insulation degradation after long-lasting nonvoltage state of the system

The paper presents electrical strength estimation of vacuum insulating system after long period of storage, when voltage was not applied to the system. The test objects were commercially manufactured, high voltage extinguishing chambers of vacuum interrupter. The method of chamber preparation with conditioning process was described. Maximum charge of microdischarges and also microdischarges onset (inception) voltage were the parameters taken as the criteria to evaluate the electroinsulating state of vacuum system. It was found that there is a relation between breakdown voltage and the charge of microdischarges. The measurements were made after long-lasting period of time, when the chambers were stored without any voltage applied to them. The investigations proved that the increase of microdischarge charge resulted in the breakdown voltage decrease. On the other hand, microdischarge charge decreasing was accomplished by the breakdown voltage increase. Limiting of microdischarge intensity involves the increase of electric strength of a tested insulating system. Microdischarges maximum charge in vacuum insulating systems may be chosen as the one of quantities used for defining the electrical state of a chamber. It is important in a case when the measurement of breakdown voltage is impossible to conduct, or should not be done, because it may change the state of an investigated system.