GB803786A - Means for the grid control of a converter - Google Patents

Abstract

803,786. Converting. ALLMANNA SVENSKA ELEKTRISKA A.B. Dec. 29, 1955, No. 37211/55. Class 38 (2). A polyphase converter 16 has floating grids 15 so energized that the grid of each non- firing anode remains negative relative to the grid of the firing anode, except that when it is to fire it receives a sudden positive rise in voltage. Suitable grid voltages are derived through transformer 12 from a mesh connection of three self-excited transductors 1, 2, 3, each in series with a resistor 4, 5, 6. This mesh connection is energized from a three-phase supply 7, the supply to the delta connected primary winding of grid transformer 12 being taken from the junctions of transductors and resistors supplied from the same phase. The phase of the sudden changes in grid voltage is changed by varying the current through series connected transductor control windings 18. For a six-phase converter the grid transformer secondary windings may comprise two independent three-phase windings 13, 14 for a converter having groups of anodes supplied from transformer winding groups connected through an interphase transformer, or a sixphase fork winding, Fig. 2 (not shown). The resistance voltage drop in the transductors may be compensated by deriving the grid transformer input voltage from autotransformers connected across resistors 4, 5, 6, Fig. 3 (not shown). An arrangement for a three-anode converter is described, Fig. 4 (not shown). Fig. 7 shows an arrangement of three transductors each comprising two cores having four windings 58, 59, 60, 61. Power windings 58 are connected in series with rectifiers 62, 63 for self-excitation, and with windings 59, 60 on the other transductors. Greater current in one transductor raises the currents in the other transductors through these windings. The control windings 61 are all in series. "When the anode grids are in two groups controlling anodes, supplied from transformer secondary winding groups connected through an interphase transformer, balance between groups may be obtained by the control windings on one core of each transductor of each group being connected in series. The four groups so formed are connected as a bridge, the diagonals of which are supplied with control current and balancing current from unbalance between the two converter groups, Fig. 8 (not shown). The steepness of the change of voltage may be increased by adding to the resistor voltage, a voltage derived from the secondary winding 79 of a transformer 78 connected in series with resistor 76, and transductor 77, Fig. 9.