GB738453A - Improvements in and relating to phase balancing systems - Google Patents

Abstract

738,453. Phase-changing. GENERAL ELECTRIC CO. Sept. 16,1953 [Sept. 17, 1952], No. 25636/53. Class 38 (2). In a 3-phase to single-phase converting system in which the 3-phase supply is balanced by connection of a capacitor and an inductor respectively across the remaining phases, the values of these reactances are automatically controlled in accordance with the current and/or voltage in the loaded phase. The load is connected across phases 2 and 3, and a saturable reactor R across phases 1 and 2. The reactor has a constant bias winding 12 opposing a control winding 11 which is connected across one diagonal of a full-wave connected bridge of grid-controlled vapour-filled rectifiers 5, 6, 7, 8. The rectifiers are controlled in accordance with the magnitude of the current in the single-phase supply line, measured by transformer 15, plus the voltage of the loaded phase measured by transformer 17. An increase in line current, or a drop in phase voltage due to increased loading, reduces the output of the rectifiers 5 ... 8 and the bias winding 12 causes the effective saturation to increase so that the reactor R increases its lagging current. The capacitor C is effectively shunted by reactors 9, 10 and the rectifiers 5 ... 8, so that reduced current through the rectifiers increases the leading current due to the capacitor. In a modification, Fig. 2 (not shown), separate sets of rectifiers control the saturable reactor and the capacitor. In a second embodiment, Fig. 3 (not shown), the reactor and capacitor are connected to the three-phase system by a step-down transformer, and the load (an electric train) by a Scott-connected transformer. The load may be supplied from either of two phases of the supply and a relay automatically changes over the positions of the balancing reactor and capacitor.