Patent GB-842412-A (GB)
Title: Improvements in or relating to on-load transformer tap changing systems
Inventor: BOOKER FRANK
IPC: H01F29/04
Filed: 1956-11-01
Abstract: 842,412. Transformers. GENERAL ELECTRIC CO. Ltd. Oct. 28, 1957 [Nov. 1, 1956], No. 33378/56. Class 38 (2). An on-load transformer tap-changing system comprises a tapped winding 11 and an auxiliary winding 12 which are connected by means of two-ganged selector switches 15, 16 so that (a) the tapped and auxiliary windings may be in in series to boost another voltage, (b) the tapped winding alone boosts the voltage, (c) the tapped winding alone bucks the voltage, (d) the tapped and auxiliary windings together buck the voltage. The voltage so controlled may be that of a main winding 10 on the transformer as is shown or some other voltage. Each selector switch 15, 16 has two contact arms which bridge a contact ring with contact segments of different sizes, and each may take up eight positions. The tapped winding 11 has nine positions and a neutral position N connected to a continuallyrotatable main selector and tap-changing is performed, utilizing a resistance 13 and switch 14 in known manner. The four stages (a), (b), (c), (d), arise on running through the positions of the main selector switch four times, and during each run through the selector switches 15 and 16 are moved round two steps, so that from maximum boost to maximum buck the switches 15 and 16 are rotated through the eight positions. The position shown is one of maximum boost, the current path being shown in heavy print. Tap changing proceeds from position 9 to 8 and on to 3, but before moving to 2, switches 15, 16 are moved one step clockwise, the circuit not being changed as the segments involved are sufficiently large. Tap changing proceeds through position 2 and 1 to N, when current flows through the circuit 131, 10, 14, N, 32, 24, 12, 28, 30, 31. Selectors 15, 16 are moved another step before moving from N to position 9, whereupon the arm of selector 16 contacts segment 22 during a period when current does not flow in part 11 so that selectors 15 and 16 do not make or break current. During the change from N to 9 there is a duplicate circuit partly through winding 12 and partly through winding 11. On position 9 current flows through 131, 112, 9, 11, 22, 30, when tapped winding 11 alone boosts the voltage. Stage (b) is then performed, tap changing proceeding from 9 down to 3 when selectors 15, 16 are rotated one step and then continuing through 2 and 1 to N when current flows through 131, 14, N, 32, 29, 31 and there is neither buck nor boost. Before moving to position 9 again to commence stage (c) the selectors 15 and 16 are again rotated one step and at position 9 current flows from 131 through 112, 9, 17, 19, 30 so that the small portion 9-17 bucks the voltage. This bucking voltage increases as tap-changing proceeds through 9, 8, 7, &c., and stage (c) is completed. Stage (d) is performed in a similar way, the selector switches being moved one step whenever a change is made from 3 to 2 or from N to 9, and eventually windings 11 and 12 are connected to provide maximum buck. The arrangement is such that movement of the selector switches 15 and 16 never makes or breaks current. Specification 842,411 is referred to.