Vacuum arc research expands interpretation of test data from vacuum interrupters

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 gap-current 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 high-current arc column. This information enhances the statistics we use in single-phase pass/fail testing of interrupters to assess manufacturing quality and the probability that new designs will 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.