GB551297A - Transformer - Google Patents

Abstract

551,297. Transformers. STANDARD TELEPHONES & CABLES, Ltd. May 8, 1942, No. 6226. Convention date, May 8, 1941. [Class 38 (ii)] [Also in Group XXXIX] A transformer for coupling a line 13 which is balanced with respect to ground to an unbalanced line 14 in a manner which minimises the transfer of longitudinal disturbing currents in the balanced line comprises two lengths of twisted quad 11, 12, mounted side by side on a support 10 and wound in opposite directions the primary and secondary windings each being composed of two wires of each quad in series, as shown in Fig. 2. The windings are grounded at their midpoints 16, 17 and the line 14 is connected to the points 2, 17. If, however, two balanced loads 15, 151 are to be fed, a further connection is made to the point 6 over a switch 31. The arrangement of the winding sections balances out the couplings between the primary and secondary that are due to longitudinal currents in the line 13, but there remain couplings between the component sections of each winding which tend to raise the potential of the ungrounded side of the line 14. To balance this effect, the other side of the line 14 is connected to the grounded point 17 through an adjustable resistance 21 which receives current from the two sides of the line 13 through adjustable condensers 19, 20. The shunting effect of the last-mentioned couplings may be counteracted by an inductance and condenser in series with the primary or secondary, these elements preferably resonating at the midfrequency of the transmitted band. The transformer is enclosed in a shield 18.