GB599519A - Improvements in the grid control of mercury vapour rectifiers - Google Patents

Abstract

599,519. Control of D.C. motors. SOMERVILLE, T. B., and MARSHALL RICHARDS MACHINE CO., Ltd. Sept. 26, 1945, No. 24939. [Class 38(iii)] [Also in Group XXXV] A D.C. motor is fed through a mercury vapour rectifier having grids supplied through condensers and inductances each with a separate D.C. saturating winding, the armature being connected between the neutral point of the rectifier transformer and the rectifier cathode, and the field winding being connected between the cathode and the neutral point of a separate secondary winding, while the saturating windings are supplied from a variable potentiometer connected in series with the field winding. In the application of the invention to the control of a D.C. motor 10, the anodes 24 of the rectifier 5 are supplied through a transformer 7, the motor armature being connected between cathode 9 and star point 8 of transformer 7. The grids 4 are supplied through condensers 1, inductances 2, and transformer 6. The inductances have windings 13, connected in series with the motor field winding 11 and are supplied with D.C. between cathode 9 and the star point 12 of further secondary windings of transformer 7 associated with further anodes. By manual adjustment of a potentiometer 14, the current through windings 13, and also the potential of star point 15 of the secondary windings of transformer 6 are varied, providing phase-shift and biasshift control respectively. A modification is described by which overload protection or load limitation for controlled acceleration can be introduced, in which the armature current passes through a winding of an automatic regulator of the vibrating type in the D.C. supply to the windings 13, Fig. 2 (not shown). Alternatively'the armature load or a proportion determined by a shunt which may be the motor series or interpole winding, may pass through second windings on the central limbs of inductances 2 which may be completely saturated at maximum load so that the current through windings 13 exercises no control. The automatic control may be used to provide constant or limited speed, horse-power or torque.