Electrical strength increase for vacuum gap containing insulator

An insulator in the vacuum gap produces peculiar conditions: (1) insulator gets charged both by DC current and by pulsed current at very low field strength; and (2) there is a dependence on insulation shape and the angle of its inclination in respect to the electrode. These regularities are explained by processes in pores of cathode “triple point” and their interaction with anode “triple point”. A specially kept gap between insulator and electrode defines the value of breakdown voltage for any polarity of the system. The same was observed for pores of like size in metal electrodes. The pores of the “triple point” result from poor contact of insulator and electrode or appear following heating, this being proved by electron microscopy. Processes in pores, i.e. switching on of self-sustaining gas discharge explains charging of insulator in the vicinity of cathode “triple point” at very low values of electrical field strength. When degassing electrodes with insulator by means of durable evacuation, heating and microdischarge training linear part of VCC with notable (10^-9-10^-5 A) current value appears. It is usually taken for conductivity currents of the insulator. This paper presents the results of experiments conducted in order to find means to prevent production of pores at low temperature bake-out