Patent GB-213978-A (GB)
Title: Improvements in insulating means for high potential terminals, conductors and the lik
IPC: H01B17/28
Filed: 1923-01-10
Abstract: 213,978. Coursey, P. R., and Dubilier Condenser Co. (1921), Ltd. Jan. 10, 1923. Condensers.-A high potential conductor or terminal is insulated from a relatively low potential, or earthed, member through which it passes or by which it is supported by means in which the solid insulating material used is so disposed that in positions adjacent to the zone or region of greatest electrical stress (that is to say the region in which the two conductors are nearest to one another) the distance between the insulater and the high potential conductor is greater than the distance between the low and high potential members. No part of the insulator lies within the gap between a high potential conductor and a low potential member through which it passes and the severest electrical stress or maximum voltage gradient is placed entirely upon a fluid insulating medium. The arrangement of insulator and conductors is preferably such that the exposed surfaces of the former conform substantiallv to the lines of force in the electric field. The voltage gradient may be made uniform by electrostatic shields or metallic rings serving as potential dividers. The low potential member may be shaped as a torus ring in the vicinity of the greatest electrical stress, and this part may be immersed in oil or other insulating fluid. Fig. 3 shows a high potential conductor 4 passing through the wall 5 of a tank 6 such as a casing for an electrostatic condenser for radio or high frequency current. The earthed member 5 has a torus ring 13 formed around the opening which may be depressed within the casing to admit of oil immersion. The insulator supporting the terminal of the high potential conductor may be of hollow frusto-conical shape and is so disposed as to comply with the conditions set forth above. An electrostatic shield 12 is mounted upon the terminal and a second one is secured to or formed integral with the tank so that the electric field shall be substantially parallel to the exposed surface of the insulator. A screwed ball or nut may be provided for external connections. The insulator may be built up of two or more parts 27, 28, an electrostatic shield 31 being preferably interposed at each joint. The conductor 4 may be supported inside the casing by a similar insulator or distance piece with or without an electrostatic shield such as 12. In one form a series of posts or columns secured between a shield or the condenser parts and the plate 5 take the thrust of the securing means. Fig. 6 shows a construction built up of mica plates clamped between shield plates 20, 21 and the low potential member 15 by nuts threaded upon the high potential conductor. The edges of the members 15, 20 and 21 are rounded and intermediate electrostatic shields, or rings of tin foil interleaved between the mica laminations, may be used to equalize the potential gradient; the rings of foil should be of smaller size than the mica. To assist in securing a smooth straight surface for such an insulator it may be impregnated with a wax or similar adhesive insulating compound. Specification 195,266 is referred to.