GB419283A - Improvements in or relating to tap changing apparatus for electric transformers - Google Patents

Abstract

419,283. Transformers; automatic regulators ; regulating switches. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, WILSON, W., and GIBSON, J. W., c/o General Electric Co., Witton, Birmingham. March 6, 1933, No. 6797. [Classes 38 (ii) and 38 (iv).] In on-load tap changing apparatus for an electric transformer a movable contact device is arranged to effect tap changing by rolling over a fixed contact device and is associated with means for preventing short-circuiting of sections of the transformer windings. A torque motor may be provided to operate the movable contact device and produce automatic voltage regulation. A three phase star connected autotransformer is fed from the mains 1 and connected to the load bus-bars 16 through a tap changing apparatus which is operated automatically by a torque motor 8 connected to the mains 1. Each phase has a set of ten fixed insulated segments 3, each set being arranged in the form of an arc having the motor shaft 9 as centre and each segment being connected to an appropriate tapping point. A disc 11 is keyed onto the shaft 9 and carries three flat springs 12 anchored at their ends to the disc 11 and each having a sector 10 pivoted to its centre. Each sector 10 is provided with twenty insulated segments 4 of approximately half the width of the fixed segments 3, adjacent pairs of the segments 4 co-operating with each of the segments 3. The two sets of alternate segments 4 of each of the movable contact devices are respectively connected by lines 6 and 7 to opposite ends of choke coils 5 which prevents short circuiting of sections of the transformer winding when tap changing takes place. The load bus-bars 16 are connected to the lines 7 through lines 17 as shown. When the mains voltage rises the torque motor 8 which is controlled by the spring 14 rotates the disc 11 in an anticlockwise direction so that the movable contacts 4 roll over the fixed contacts 3 and tap changing takes place to reduce the number of secondary turns and maintain the voltage at the lines 16 approximately constant. Co-operating teeth may be provided to ensure that the fixed and movable contact devices remain in the correct spacial relationship. The torque motor may rotate the disc 11 through suitable gearing and may be fed from the bus-bars 16 the spring 14 being replaced by a gravity operated controlling means and damping means being provided to reduce hunting. The arrangement may be modified to employ a series boosting transformer in place of the autotransformer.