Operational conditions influencing the partial discharge performance of cables under low and medium vacuum

The performance of flexible cables for applications at the kilovolt level over a gas pressure range from below 1 Pa to ambient needs to be quantified. Braided cable designs provide the flexibility, but necessarily contain voids where at certain pressure values the Paschen minimum voltage can be exceeded. In our prior research a methodology was proposed based on partial discharge diagnostics. However, the reproducibility needs to be investigated in view of the stochastic occurrence of the discharges in cable voids differing in shape and size. From a cable with braided screen, the variation of the partial discharge inception voltage as function of pressure is characterized, both for tests on different samples and for consecutive tests on the same sample. Variation between different samples is significantly larger, but overall the performance is reproduced within typically 20%. Based on analysis of variance, results are found to be robust against experimental parameters defining the partial discharge inception criteria. In addition, the influence of external parameters such as temperature, magnetic field and radiation exposure, which can be part of the operational conditions of equipment, is investigated. It is found that temperature rise resulted in a performance increase of the cable, which is not in line with expectations from the change in gas density but may be attributed to reduced secondary electron emission. Exposure to magnetic field and γ-radiation did not show noticeable effect.