Patent GB-268765-A (GB)
Title: Improvements in or relating to tap-changing systems for electric transformers
IPC: H01F29/04
Filed: 1927-03-24
Abstract: 268,765. Metropolitan-Vickers Electrical Co., Ltd., (Assignees of Dann, W. M., Hill, L. H., and Sipher, E. F.). March 31, 1926, [Convention date]. Regulating transformers.-The voltage ratios in a plurality of connected transformers are controlled simultaneously by tap-changing mecha.- nisms whose operations are initiated by a control switch, the mechanisms then continuing to operate through a predetermined cycle independently of the control switch and of each other. Fig. 1 shows the operator's panel with the forward and reverse control switches 8, 9; Fig. 2 shows the first transformer 1 of a set of three similar transformers, with its control panel, which panel has in addition a single pair of master relays 6, 7 with three-pole contacts connected to sets of contactors 4, 5 provided on the control panels of all the transformers. Indicators 12 shows the positions of the tap-changing mechanisms of the transformers, and relays 13 controlling indicating lamps 14 are operated by conditions of unbalance in the transformers. A time-limit relay 15 controls a secondary alarm 16 or circuit interrupter. Each transformer comprises a high-tension winding 21, with manual tap-changing device 23, and parallel lowtension windings 24, 25, each with tap-connections connected to the cam-operated switches 26, 27, of which switches one in each group is normally closed. The winding whose tap connections are to be changed, is opened, the other winding temporarily assuming the transformer load. Driven interrupters 28, 29 prevent arcing. The cams of the tap switches 26, 27 are on a shaft 31 driven by a motor 34 from a main shaft 30 which also operates cam-operated pilot switches 36 - - 39, 41 forward and reverse limit switches 42, 43, and an indicator 44 which controls the corresponding indicator 12. Switches 37, 39 are normally closed when the transformer is operative, but one or other is opened during tap-changing (forward or reverse), switch 38 or 36, normally open, being closed and opened during that period. Switch 41 is connected to one of the relays 13 and to a bell or circuit. breaker trip coil. On each transformer controlpanel are the two-pole contactors 51, 65 for forward and reverse changing respectively, threepole contactors 54, 58, 68, 74 (the contactors 58, 74 also having back contacts 63, 78), and a twopole knife-switch 88, 89 connected to the Band D conductors of a two-phase four-wire alternating supply A - - D. On closing control switch 8 to initiate tap-changing in the forward direction. the master relay 6 is energized by a circuit including switch-blades 88, 89 and leads 103, 100, 104, closing contacts 81. 82, 83 for the three transformers. Contact 81 completes a circuit between switch-blades 88, 89, including leads 113, 114, 115, 104, forward limit switch 42, and the contactor 51 which closes switches 52, 53. Switch 52 closes a holding circuit for its contactor 51, independent of control switch 8 and master relay 6, which circuit extends from blade 88 to blade 89 and includes also leads 113, 125, 126, 115, 104, and pilot switch 37. Switch 53 closes a circuit energizing contactors 54, 58 in parallel, the circuit extending from blade 88 to blade 89 and including also leads 113, 128, 129, 104, and the back interlock contact 78 on one of the reverse contactors 74. Energization of contactors 54, 58 closes switches 55, 56, 57 and 59, 61, 62 respectively. Switches 56. 61 close holding circuits for their contactors 54, 58 independent of contactors 51, which circuits extend from blade 88 to blade 89 and include also leads 113, 141 or leads 144, 145, lead 142, the open pilot switch 38, lead 143, interlock 78 and lead 104. Switches 55, 57, 59, 62 complete circuits through the brushes of the motor 34, from the conductors A, C, B, D in the order named. Rotation of the motor closes pilot switch 38 and then opens switch 37, which de-energizes contactor 51; contactors 54, 58 are then energized through interlock 78. At the end of the tap changing operation, pilot switch 37 is closed and 38 opened; contactors 54, 58 are de-energized and the motor circuit broken automatically. The apparatus is then ready to adjust the voltage ratio through another step. If the control switch R is held closed, tap-changing operations proceed without pause. The operation in the reverse direction, from control switch 9, utilises the master relay 7, contactors 65, 68, 74, and similar circuits, the motor being energized in the order- C, A, B, D. The main driving-shaft 30 may also be operated by a handle 33 through a clutch 32. Specifications 268,766 and 269,156 are referred to.