Vacuum arc research expands interpretation of test data from vacuum interrupters

Abstract

Abstmet-Using high-speed movies of vacuum arcs between spiral contacts in conjunction with floating arc shields, the arc voltage, current and contact travel have been correlated with arc behaviors. These arc behaviors can be described by arc appearance diagrams in gapcurrent space. These allow the waveforms from high-power tests on spiral-contact vacuum interrupters to be evaluated for information on the internal arcing behavior and arc-induced damage. We have found that arc voltage traces can be examined during interruption testing to help in judging the probability that a vacuum interrupter will continue to pass additional interruption trials. The arc voltage also reveals signs of damage to the contacts, such as melting caused by a prolonged interval of a stationary highcurrent arc column. This information enhances the statistics we use in single-phase p a d f a i l testing of interrupters to assess manufacturing quality and the probability that new designs w i l l pass three-phase certification. Correlation of arc voltage traces with the arc appearance and arc motion is also discussed for butt-type contacts, axial magnetic field contacts, and radial magnetic field slotted-cup contacts.

The motion of vacuum arcs between spiral contacts with a fixed-polarity arc shield [in vacuum interrupters]

“…Unlike the behavior with a floating shield [3], [4], the middle section of the arc column did not totally leave the contact gap when it interacted with the shield. Rather its periphery briefly spread out radially as in Fig.…”

“…and V(9. These are compared here to results with a floating shield of the same diameter [4]. Special attention is given to describing the conditions which produced cathode spots on the shield, and how the vacuum arc modes interacted with the shield.…”

“…13 is the appearance diagram obtained with a samediameterfloating shield[4]. By comparison, the diagram inFig.…”

“…Alternatively, it can be connected to one electrode -usually to the fixed electrode through an endplate. In past studies, a vacuum chamber apparatus and a high-speed camera were used to determine arc appearance diagrams for spiral contacts of diameter I$ = 62 nim, using isolated arc shields with I$(shield)/I$(contact) equal to 3.4 [3] and 1.3 [4]. 'The present work extends those results to a case in which a Cu-alloy shield wais electrically connected to the fixed electrode through a stainless steel plate.…”

Vacuum interrupters, the new technology for switching and protecting distribution circuits

“…Vacuum interrupters also have no 'blind spots' or 'critical currents', i.e., a current range somewhere between load current and full short circuit current where the interrupter has difficulty interrupting. Beyond their full short circuit rating the probability of failure to interrupt gradually increases (15). VIS have been observed, however, to interrupt currents 25% higher than their full short circuit rating.…”