Suppression of Conditioning Effect in Vacuum by Micro-protrusions from Anode

• Main Authors: Kondo, Fuminori, Kojima, Hiroki, Fukuda, Hideaki, Sakaki, Masayuki, Hayakawa, Naoki
• Format: Conference Proceeding
• Language: English
• Subjects: Anodes; Cathodes; Shape; Surface treatment; Vacuum breakdown
• ISSN: 2643-9816
• DOI: 10.1109/ICEPE-ST.2019.8928772

Spark conditioning is an effective method to improve electrical insulation strength of vacuum circuit breakers. We discuss the spark conditioning process in consideration of the generation of micro-protrusions on cathode surface by breakdown. We conducted the spark conditioning on three pairs of rod-plane electrodes made of OFHC Cu. For one pair, the voltages were applied until conditioning saturation, namely 600 times voltage applications. For the others, a smaller number of voltage applications (100 times and 300 times) before conditioning saturation were given. After these conditioning experiments, we observed the surface of rod cathodes with a microscope. After the conditioning by about 600 times voltage applications, many micro-protrusions appeared on the cathode surface. Some of them had a diameter larger than 20 μm. They would be caused by adhesion of metallic particles from anode and remained through the conditioning process. On the other hand, few micro-protrusions were found on the cathodes with 100 and 300 times voltage applications. This means that the micro-protrusions were generated at the last period of the conditioning process. In other words, the generation of micro-protrusions can be a dominant factor of suppression and saturation of conditioning effect.