Research on the Pre-breakdown Electron Emission Characteristics of a Vacuum Gap During the Spark Conditioning Process

Spark conditioning is the process that increases the breakdown voltage of a vacuum gap by repetitive breakdowns. However, neither the mechanism of vacuum breakdown nor the mechanism of spark conditioning is fully understood. Electron emission is a key factor leading to vacuum breakdown. The objective of this paper is to study the pre-breakdown electron emission characteristics during the spark conditioning process of a vacuum gap. The experiment was carried out using a commercial vacuum interrupter (VI) with a pair of contacts made of CuCr25. Spark conditioning of the VI was carried at a gap distance of 1 mm. Waveform of the applied voltage and the electron emission current before each breakdown was used to calculate the field enhancement factor and the effective emission area using the Murphy-Good Plot. Results showed that as the breakdown voltage increased during spark conditioning, the field enhancement factor beta decreased while the effective emission area A(e) increased, with the local electrical field beta U/d and the emission current density I-e/A(e) at the breakdown moment remained almost unchanged. A linear relationship between beta and log(A(e)) was discovered. The results of this work could help understand the mechanism of vacuum breakdown and conditioning.