The Initiation of Vacuum Breakdown under Alternating Voltage

The paper presents experimental studies on the properties of vacuum insulating systems at power frequency ac voltage. The author points to differences between two kinds of voltage, dc and ac voltage, influencing then condition of insulation systems. These differences consist, first of all, in mechanical and thermal fatigue caused by ac voltage to the surface electrode layer as a result of periodic changes in the electrostatic forces effecting microprotrusions of the electrode surfaces, and periodic changes in the temperature of parts of electrode surfaces due to resistive heating of microprotrusions through which variable field emission current flows, and as a result of bombardment ent of parts of electrode surfaces with electron beams of variable density. Mechanical and thermal fatigue gradually decrease mechanical strength of some parts of the electrode material and cause separation of microprotrusions of the electrode surfaces at ac voltage at amplitudes lower than with dc voltage.