Interruption performance of vacuum circuit breaker under low- and very low- frequency condition

Vacuum interrupters (VI) are primarily used for electrical power applications at frequencies of 50/60Hz. However, other electrical power applications exist at lower frequencies. One key application is in rail power systems that operate at 25 and 16. 7Hz. Vacuum interrupters have successfully performed in these applications for many years. Recently, green energy applications can produce temporary fault conditions with even lower frequencies, such as in wind turbine, pumped storage, solar power DC to AC converters, and shipboard applications. The challenge in low frequency applications stem from the very long arcing times and high transferred charge for a given current level. This paper presents the calculated theoretical boundary of the interruption performance down to frequencies of 0.5 to 2Hz and compares it to the cases at 16.7 and 50Hz. In addition, experiments were performed concerning the arc impact on the VI including metal vapor deposit on the ceramic, and heat build-up in the contacts and shields surrounding the arc chamber. The arc erosion rate of the contacts was also calculated for short-circuit conditions from 10.40kA at 50Hz, and at frequencies of 0.5 to 5Hz with currents of several hundred amperes. Comparison to certain certification test conditions is made, such as the delayed current zero (CZ) and very high DC current offset tests in the generator breaker standard, that are effectively tests at lower frequencies.