GB1411493A - Excess voltage arresters - Google Patents

Abstract

1411493 Spark gaps M-O VALVE CO Ltd 21 March 1974 [23 March 1973] 14139/73 Heading H1D A spark gap arrester as described in Specification 1,021,782 has electrodes 10, 11 in a gasfilled housing comprising end caps 1, 2, insulating sleeves 4, 5 and a central conducting portion 3. The D.C. breakdown voltage across the gap 17 or 18 between either electrode 10 or 11 and the portion 3 is less than the breakdown voltage across any gap between a point on the surface of that electrode 10 or 11 and any conductive coating which may be produced on the inner surface of the adjacent insulating portion 4 or 5, and means are provided for restricting the cathode spot formed in operation on the inner end of either electrode 10 or 11 to a region adjacent the inner end of that electrode. The construction of the electrodes, the filling of the device with gas, and the connection of the arrester in an electrical circuit, and the dimensions and breakdown voltages, are as in Specification 1,411,492. The inner ends of electrodes 10, 11 are coated with electron emissive material, which anchors the cathode spot formed on either electrode, reducing, but not eliminating, sputtering on to the end faces 21, 22 of the sleeves 4, 5. Coatings so formed are connected to earth via central portion 3, but the gaps 17, 18 have breakdown voltages below that between the coatings and the portions 13b or 15b of the electrodes 10, 11. The movement of cathode spots may be restricted by, instead of electron emissive coatings, sleeves of insulating material as in Specification 1,411,492. These sleeves also increase the breakdown voltage between coatings on end faces 21, 22 and the adjacent electrodes 10, 11.