Experimental Evaluation of the High-Current Drawn Arc Energy Balance

The distribution of energy between anode and cathode of high-current drawn vacuum arc has been experimentally evaluated for different CuCr based contact materials. The energy distribution was determined by measurement of the temperature rise with one thermocouple soldered into drilled hole in the holder of the electrode, which was in turns cathode and anode. The measurements were carried out in the commercial vacuum interrupter, 36-55mm in diameter AMF electrodes were made from SSS CuCr 70/30 and LSS CuCr 50/50. The contacts were separated by magnetic actuator with stable and invariable average opening speed 1m/s, maximum contact distance was 7mm. The arc duration was 8.5-9.5ms in all the tests. The study of material influence on the energy distribution has been done for the typical range of currents for commercial vacuum interrupter 5kA - 40kA and for the extreme, knowingly overheating regime with current 60 kA

I. Introduction

Dielectric strength of the vacuum gap after the arc burning is lower then the dielectric strength of the cold gap. Prevalent explanation is based on Paschen mechanism of hot breakdown – the breakdown in metal vapour that originates from the molten electrode zones and found in the gap up to some ms after current zero [1], [2]. Such obvious connection between hot vacuum gap breakdown characteristics and contact surface temperature stimulated direct measurements [3], [4] and theoretical estimations of «the temperature of failure>> [5]–[8]. The correctness of any heat calculations in this case is determined not only by knowledge of thermophysical properties of the contact material, but also by knowledge of arc energy distribution between anode and cathode.