GB254771A - Improvements in electrical protective arrangements for alternating current systems - Google Patents

Abstract

254,771. Brown, W. J., and Metropolitan-Vickers Electrical Co., Ltd. March 10, 1925. Cut-out arrangements.-Relates to protective systems for alternating current circuits in which pilot wires are dispensed with by the use of oscillators which supply high frequencies superimposed upon and derived from the line so that the frequencies are generated for positive or negative half cycles of the line current, and in the event of fault or phase displacement set up or diminish the beat frequencies arising from the two superimposed frequencies as described in Specifications 252,036, 252,810, and 254,770. According to the invention the oscillations are generated continuously from a separate source and are superimposed on the line, positive or negative half cycles being damped out during either positive or negative half cycles of line current or of a current representative thereof. In the arrangement shown a triode 5 with a tuned anode coil 7 coupled to a grid coil 6 is supplied from a high tension battery or D.C. generator 9 and supplies continuous oscillations to the line through the coupling 11 and condensers 12 or by other known means. These oscillations are damped out for one halfcycle of the line current by means of a triode or, as shown, a diode 13 acting as an absorption valve with its anode connected to the grid coil and its cathode connected to a transformer 14 in the line. The battery 18 constitutes an anode bias for the diode, and the battery 19 a grid bias for the oscillating triode in place of the more usual grid condenser and leak. The transformer generates a high voltage to give a sharp cut off. The protective relay is indicated at 4. The diode 13 substantialy short-circuits the grid coil 6 and therefore damps out the oscillations for halfcycles of the line current. A high and preferably supersonic beat frequency is employed as described in Specification 252,810 referred to above.