GB370405A - An improved process and apparatus for the protection of rectifiers against excess currents - Google Patents

Abstract

370,405. Rectifying alternating current. LUTZ, F., 32, Sulgenauweg, Berne, Switzerland. Oct. 2, 1930, No. 29560. Convention date, Oct. 3, 1929. [Class 38 (ii).] Mercury vapour or hot cathode rectifiers are protected against overload or short-circuit conditions by means of grids associated with the anodes and so energized in accordance with load conditions that above a predetermined load the moment at which the anodes start to conduct is retarded thus reducing the output voltage of the rectifier. Fig. 1 shows a mercury vapour rectifier comprising anodes A associated with grids G and a cathode K in which retarding of the ignition under abnormal load conditions is effected by imparting to the grids a negative voltage due in part to the drop across a resistance W carrying the load current and in part to the voltage produced by a rise in load current in a transformer T, this voltage being neutralized under normal load conditions by a battery B providing positive bias. In an alternative arrangement, Fig. 2 (not shown), grid voltage is derived from a pair of opposed windings inductively associated with the circuits of different anodes. In a further arrangement, Fig. 3, in which the grids G are normally positively biassed by a battery B or an auxiliary rectifier, ignition is retarded under abnormal conditions by increase in the voltage of a condenser C opposed to the battery B and charged through rectifiers V by transformers T.