GB822000A - Improvements in or relating to spark gap apparatus - Google Patents

Abstract

822,000. Spark apparatus. STANDARD TELEPHONES & CABLES Ltd. June 30, 1958, No. 20832/58. Class 39(1). Spark gap apparatus comprises spaced main electrodes having concentric opposed surfaces, a single stationary trigger electrode insulatingly disposed within one only of said main electrodes and having its tip standing in a central aperture in said main electrode, the trigger electrode being adapted to fire the main spark gap by causing a field distortion in said main spark gap, and a pot magnet concentric with said electrode array for creating a radial magnetic field in said main spark gap. In the arrangement shown the pot magnet has an outer annular pole 24 attached to a cylindrical insulator 25, and an inner annular pole 26 to which a main electrode 27 is attached. The electrode 27 is connected by a strap 28 to a terminal 29 which passes through an insulating bush 30 to an earth connection 31, so that during operation the discharge current is prevented from passing through the pole 26. The magnet is energized by a winding 32 having two d.c. connections, one of which is shown at 33. The trigger electrode 34 is carried by an insulating member 36 which is surrounded by a metal sleeve 37 forming an electrostatic screen. The form of the member 36 is such as to encourage local corona discharges which assist the trigger effect. The other main electrode 39 is carried by a rod 40 threaded into a metal end cap 41 carrying an H.T. terminal 42. Air under pressure from an inlet 44 enters the enclosure through a channel 45 in the vicinity of the trigger electrode 34 and is discharged through a restrictor valve 46. Owing to the shape of the electrodes 27 and 39, a discharge originating near the axis will move radially outwards very rapidly so as to flow across the shortest possible gap, and is then rotated by the magnetic field, thus reducing erosion of the electrodes. In a simplified arrangement, Fig. 3 (now shown), a permanent pot magnet is used and the electrodes are not enclosed.