Voltage Breakdown Testing of Relays in the 1000-V Range

The ac voltage breakdown between adjacent conductors separated by an insulator on relays has been examined using two types of breakdown test sets and a sensitive corona (partial discharge) detector. A large difference in the breakdown voltages was observed on relays from the same population using two breakdown test sets. The characteristics of the test sets were examined to identify the cause of the breakdown difference. The breakdown voltage is independent of the voltage ramp speed from 55 to 8300 V/s. It is also independent of the series resistance up to 300 kOmega. The different detector systems do not contribute to the breakdown difference. The output capacitance of the breakdown test sets appears to be quite important to the voltage breakdown of the samples. Modification of the output of the test sets leads to similar breakdown values. The prebreakdown discharges observed using the corona detector suggests that breakdown is a gas breakdown type. Effects on the insulator surfaces caused by the testing are considered in light of the prebreakdown discharge measurements and are expected to be minimal. These results should be applicable to the moderately high voltage testing of other products, although the numerical values will probably differ.