GB406651A - Improvements in or relating to backfire-preventing means for rectifiers - Google Patents

Abstract

406,651. Inductances. WESTING- HOUSE ELECTRIC & MANUFACTURING CO., East Pittsburg, U.S.A.-(Assignees of Slepian, J. ; 1115, Lancaster Street, Pittsburg, U.S.A.) May 30, 1932, No. 15270. Convention date, July 4, 1931. [Class 37.] Relates to means for preventing backignition in rectifiers. The Specification states that the initiating cause of a back-fire is active only for a small period of time, of the order of a few micro seconds, and if the current is prevented from rising to a value sufficient to sustain an arc during a period slightly greater than the active period, the backfire will be prevented from becoming effective. The means consists of a reactance designed to saturate at a very low value of current (smaller than that necessary for a self-sustaining arc) the time taken to saturate being greater than the period of activity of the back-fire initiating cause. This reactance is connected in series in the anode lead. A theoretical discussion of the design of such a reactance together with a consideration of the effects of eddy currents on the design is given in the Specification. Fig. 3 shows the response curve for such a reactance in which the current is plotted to a time base, and it will be seen that the current remains practically constant at a low value during an initial time period. Since the reactance has to stand the full load current it is preferably constructed in the form of a single layer winding on a ring core. This core may be reduced in cross-section at one point in order to adjust the saturation value. In a multi-phase rectifier, Fig. 5, two anodes may be fed from a single phase through a reactance 51 designed as above but having two windings arranged so that they are non-inductive when the anodes are normally conducting current. Since the self-capacity of the winding may effect operation various means are employed to counteract this. In Fig. 12 the winding 80 is completely embedded in the core which is composed of slotted laminations 78 and ring laminations 81, 82. In a modification, Fig. 13, the turns 84 are uniformly spaced between the core 85 and a shield 86. In a further modification, condensers are connected between the turns and one end, and in another modification between the turns. Since a high potential is built up across the reactance during the back-fire initiating period, protective means are provided such as lightning arresters connected between the grids or resistances or condensers connected between the anodes and cathode.