The surface of a solid dielectric insulator becomes electrically charged when subjected to a high-voltage stress in vacuum. A method for calculating the surface flashover voltage based on the assumption that the discharge occurs in a layer of desorbed gases from the insulator surface is proposed. The electric field strength required to cause surface flashover is calculated by taking into account the secondary electron emission characteristics of the dielectric material. The dependence of the surface flashover field on the insulating material is deduced. A dependence of the flashover voltage on the insulator length to a power law of 0.5 is theoretically predicted. The calculated surface flashover voltage is compared with the previously reported measurements and good agreement is obtained.

The surface flashover of Teflon, plexiglass, quartz, Pyrex glass, Macor glass-ceramic, and sapphire solid insulators has been measured in vacuum (∼10−8 Torr, ∼10−6 Pa) and in atmospheric air using dc, ac (60 Hz), and 1.2/50-μsec lightning impulse voltages. The dependence of the flashover voltage on the following parameters is investigated: (1) spacer material, (2) diameter of the spacer, (3) spacer length, (4) number of spacers stacked in series, (5) air pressure in the range 10−6–105 Pa, (6) electrode material, (7) spark conditioning, and (8) the external resistance in series with the gap. At a fixed insulator length the flashover voltage decreases with increasing spacer diameter. The withstand voltage of spacers stacked in series increases with increasing the number of spacers. The dc flashover voltage of different insulating materials is theoretically calculated in vacuum as a function of the length of the insulator and compared with the experimentally obtained results. Good agreement is obtained.

The surface flashover of a Macor glass-ceramic conical insulator in ultrahigh vacuum is investigated using direct current (dc), alternating current (ac at 60 Hz), standard lightning impulse (1.2/50 μs), and combinations of dc+1.2/50 μs and dc+ac. The dc and the 1.2/50-μs flashover voltages are found to be at about the same level when the cone angle θ, which the surface makes with the applied field, is varied from −55° to +55°. At a fixed positive value of θ and a fixed thickness of the insulator, the lightning impulse, and the dc flashover voltages are higher than the ac. The level and the polarity of the dc prestress influence the combined dc+impulse flashover voltage in conical insulators. The ac+dc flashover depends on the dc prestress level and increases with increasing the prestress until a saturation is reached which is at a slightly higher voltage than the dc flashover. The electric field and the potential distributions at the interface of the cone insulator are calculated for different cone angles in the range 5° to 55°.

in the full system development, which included subsystem level technologies involving Aeronautics, Mechanical and Chemical Engineering, Laser and Optics and Diagnostics and Instrumentation. He has published 14 papers in national and international journals and reports. He is a member of Indian Laser Association, ILA and many awards to his credit.

Articles you may be interested inSelf-consistent simulation of the initiation of the flashover discharge on vacuum insulator surface Phys. Plasmas 19, 073516 (2012); 10.1063/1.4737195 Surface flashover of solid insulators in atmospheric air and in vacuumThe influence of the metal-dielectric junction on the electric field distribution along the solid insulator-vacuum interface is analyzed in detail in two widely used electrode-insulator geometries: (1) a cylindrical solid insulator with metal inserts at both ends and (2) a cylindrical solid insulator placed in recessed electrodes at both ends. The effects of the length of the metal inserts and the angle t/J between the solid insulator and the recessed electrode on the electric field and the flashover voltage have been theoretically investigated and experimentally validated. The permittivity of the solid insulator materials used is varied from 2.1 to 100, The surface flashover voltages of Macor glass ceramic and Teflon are measured in vacuum ( < 10-8 Torr) in different electrode-insulator contact geometries using dc, ac (60 Hz), and 1.2/50-,us lightning impulse. The measurements show good qualitative agreement with the behavior predicted from the computation.