The role of emission properties in non-sustained disruptive discharge (NSDD) evolution

The peculiarities of field-emission current and NSDD-capability of SSS CuCr 70/30 vacuum gap have been investigated for the commercial vacuum interrupters. It has been found that 1) NSDD is not a result of long-term (more than 100 mus) increase of field-emission current; 2) there is no correlation between average level of emission current and NSDD capability of vacuum gap; 3)there is a strong correlation between NSDD-capability of the contact gap and capability of the gap to generate sharp short-term bumps of the emission current; 4) NSDD and the bumps of the current (often) are followed by the step increase of average emission current, return to the initial value takes the emission current several following periods of applied 50Hz voltage. It has been determined that the duration of the bumps is not more than 10 mus and the bumps are not preceded by field-emission current increase. It has been demonstrated that under the test condition the phenomena of current bumps can not be explained by the mechanism of explosive auto emission. The authors suppose that NSDD and current bumps have the same origin - the bombarding of the contact surface by the particles