Patent GB-440739-A (GB)
Title: Improvements in electric transformers particularly adapted for grid-controlled gaseous discharge tube apparatus
IPC: H02M1/04
Filed: 1934-07-06
Abstract: 440,739. Rectifying alternating current; phase changing ; transformers. STANDARD TELEPHONES & CABLES, Ltd., 63, Aldwych, London.-(Assignees of MatÚriel Telephonique Soc. Anon. ; 46, Quai de Boulogne, France) July 6, 1934, No. 19897. Convention date, July 12, 1933. [Class 38 (ii)] A transformer for producing voltage impulses of adjustable phase, e.g. for energizing the grids of mercury vapour rectifiers comprises a primary winding 26, a secondary winding 24 on a core limb 23 operating at saturation, and a D.C. excited control winding 25 whereby the point on the primary current wave at which the limb 23 saturates may be varied, thus shifting the phase of the voltage impulses generated in the secondary. A magnetic shunt path including symmetrically disposed air gaps 21, 22 is provided between the primary and secondary windings. The voltage impulses generated in the secondary may be totally suppressed by increasing the current in the control winding to a point at which the core is completely saturated.. Alternatively, this effect may be achieved without shifting the phase of the impulses by providing a pair of parallelconnected secondary windings on separate core limbs which also carry a pair of opposed windings. On supplying D.C. to the latter, the impulses generated in the two secondaries are phase displaced in opposite senses, and since the secondaries are in parallel, each forms a short-circuit path for the impulses generated in the other. Fig. 5 shows a polyphase rectifier installation, in which three valves 60, 61, 62 are regulated manually and automatically by three transformers having control and suppressor windings as described. Each transformer comprises a primary 63, a pair of secondaries 78, a manual control winding 70 supplied with D.C. through an auxiliary rectifier 67 and regulating resistance 66, an automatic control winding 75 supplied from a shunt 72 in the rectifier load circuit (if desired through a resistance 76 which varies with current to modify the regulation characteristic) and a pair of suppressor windings 83 to which current is supplied to effect suspension of the operation of the rectifier by suppression of the grid impulses when the load current becomes excessive. The operating current for producing this effect is supplied through a relay 77, the control circuit of which is energized by the shunt 72. The relay may comprise a group of grid-controlled rectifiers, the grid circuits of which are connected across a diagonal of an inductance bridge of which the impedances in opposite arms are adapted to be varied by saturating windings energized from the shunt 72. At the critical load value phase reversal of the voltages applied to the grids of the valves is effected and the latter are rendered conductive to apply current to the suppressor windings 83. The main valves 60, 61, 62 are thus rendered inoperative and are maintained inoperative by closure of a switch which applies positive voltage to the grids of the valves of the relay 77 in response to the output current of the relay itself.