GB291003A - Improvements in or relating to a method of preventing back ignitions in metal vapour rectifiers having insulated anode sheaths - Google Patents

Abstract

291,003. Akt.-Ges. Brown, Boveri. et Cie. May 23, 1927, [Convention date]. Addition to 253,097. Vapour apparatus, arrangements of.-Relates to preventing back ignitions in metal vapour rectifiers by imparting to metal anode sheaths or grids potentials negative with respect to the corresponding anodes as described in the parent Specification, and consists in making the difference of potential between each anode and its grid dependent on load current. The anodes a<1> - - a<6> are energized from a set of secondary windings, one of which is shown at s<1>, of a main transformer having primary windings p<1>. The corresponding grids g<1> - - g<6> are energized with similar potentials from a second set of secondary windings such as s<2> either on the main or on a separate transformer. Between the two star points o<1>, o<2> is connected a small auxiliary rectifier z supplied by an auxiliary transformer, the primary p<2> of which is in series with the main primary p<1>. Under no load or light load conditions, the points o<1>, o<2> are at equal potential, the magnetizing current of the main transformer being insufficient to cause operation of the auxiliary rectifier, and consequently the grids have substantially the potentials of their associated anodes. Under load, however, the auxiliary rectifier z is rendered operative, and a D.C. voltage proportional to load current is interposed between the points o<1>, o<2> with the result that the grid potentials are rendered negative with respect to the corresponding anodes by amounts proportional to load current. The arrangement is so proportioned that above a predetermined value of load current, operation of the rectifier is interrupted either by the difference of potential between the anode carrying current and its grid becoming greater than the voltage drop in the rectifier resulting in the grid becoming negative with respect to the cathode k, or failure of the grid of the next anode in order of succession to attain a higher potential than the cathode in time for current to start in that anode. In order to prevent immediate restarting of the rectifier after cutting out, due to consequential cutting out of the auxiliary rectifier z controlling the grid potentials, a choking coil d is connected as shown so as to retard the rising of the grid potentials.