A New Measurement Method of Contact Conditions in a Vacuum Circuit Breaker With the Field Emission Current During the Closing Operation

The performance of vacuum circuit breakers (VCBs) in the interruption and protection of an electric power system is highly dependent on the contact conditions; thus, the assessment of the contact conditions is essential. The field emission current has been recognized as an effective parameter with which to investigate the contact conditions both qualitatively and quantitatively. The traditional measurement method that uses the field emission current to determine the contact conditions is performed under ac voltage and requires the VCB to be dismantled, which limits the application of this method. The objective of this study is to develop a new measurement method for the contact conditions in a VCB with the field emission current during the closing operation under dc voltage. The new measurement method does not require the VCB to be dismantled and can simplify the processing of experimental data. Then, the new measurement method is applied to investigate the contact conditions during capacitive switching. The obtained result shows that the field enhancement factor
$\beta $
of the contact surface oscillates up and down during the capacitive experiment, which can verify the conditioning and deconditioning effects of the inrush current on contact surfaces.