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 β decreased while the effective emission area Ae increased, with the local electrical field βU/d and the emission current density I
e
/A
e
at the breakdown moment remained almost unchanged. A linear relationship between β and log(A
e
) was discovered. The results of this work could help understand the mechanism of vacuum breakdown and conditioning.