GB335858A - Improvements in or relating to electric transformers - Google Patents

Abstract

335,858. Associated Electrical Industries, Ltd., (Assignees of Field, R. M.). Jan. 10, 1929, [Convention date]. Systems depending on static transformers.-In an arrangement for changing the tap connections of a power transformer 11 under load, an auxiliary transformer 32 energized from a low voltage source 34, 35 is employed, the auxiliary transformer having a pair of secondary windings 29, 31 adapted to be connected between the tapping switches 21 - - 24 and the power circuit conductor 17 through transfer switches 18, 19, the arrangement being such that tap changing may be effected without interrupting current at high voltage. Minimum voltage between conductors 16, 17 is obtained by closing switches 21, 18, 25, 26. Under these conditions, the potential of the conductor 17 is equal to that of tap 21, less half the voltage between adjacent taps due to negative boost supplied by winding 29. Voltage is raised by an amount equal to half that between adjacent taps by opening switches 25, 26 thus de-energizing windings 29. A further increase in voltage by the same amount is obtained by closing switches 27, 28 thus reversely-energizing the winding 33 and applying positive boost through the winding 29. Before making further increases in voltage, transfer switch 19 is closed bringing into circuit the winding 31 connected to the next tap. Since, however, the voltage of the winding 31 is equal and opposite to that of the winding 29, no change in voltage takes place at this stage. Winding 29 is then cut out by opening switch 18, again without voltage change. A further increase in voltage by an amount equal to half that between adjacent taps may then be made by opening switch 19 thus removing negative boost due to winding 31 and bringing conductor 17 to the potential of the second tap. Further increases in voltages are obtained by similar use of the auxiliary transformer 32.