Patent GB-1042883-A (GB)
Title: Improved electric load transfer switch
Inventor: HASELFOOT ARTHUR JOHN
IPC: H01H9/00
Filed: 1962-08-01
Abstract: 1,042,883. Variable resistors. FULLER ELECTRIC Ltd. July 31, 1963 [Aug. 1, 1962], No. 29522/62. Heading H1S. A combined switch and resistor intended for use with an on-load tap-changer comprises a pair of upstanding insulating plates 4, 5 having a pair of resistance elements 22, 23 extending therebetween. Each element 22, 23 comprises a copper end block 24, a plurality of graphite resistive blocks 25 in end-to-end abutting relationship, and an insulating end block 26. The resistivities of the blocks 25 are graded such that the resistivity increases according to the nth power of the distance (n lying between - 1 and 0) progressively from the block 24 to the block 26, the elements 22, 23 being reversibly arranged with respect to one another so that the block 24 of element 22 and block 26 of element 23 are adjacent the plate 5, the other blocks 24, 26 being similarly adjacent the plate 4. The upper and lower surfaces of the elements 22, 23 are engaged by spring-urged contact rollers 31 of roller cradles 10, 11 carried by a conducting plate 9 of a carriage 1, resilient contact blades 35 ensuring good contact between the rollers and the plate. Arcing discs 32 are provided at the ends of each roller assembly. The lower surface of the plate 9 has a toothed rack 12 having wings 15 engaging keyways 16, 17 in guide plates 6, 7 extending between the plates 4, 5. A further rack 8 is disposed between the plates 6, 7, the racks 8, 12 being engaged by a pair of pinions trasversable by an operating member 21 driven by an overcentre mechanism whereby movement of the latter causes the rollers 31 to move along the elements 22, 23. At each extremity of movement of the carriage 1 contact is finally broken with the element 22 or 23 by the arcing discs 32 coating with arc blocks 28 interposed between the blocks 26 and the adjacent resistive blocks 25; also, at each extremity of movement a solid contact is established between a pair of block contacts 36 carried by the cradles 10, 11 and pairs of contact clips 37a or 37b. The clips 37a, 37b adjacent the blocks 24 are connected thereto by terminals 29, the other pair of clips 37a, 37b adjacent the blocks 26 being connected, respectively, to a pair of contact pick-up rails 38, 39 extending between the plates 4, 5. The rails 38, 39 are engaged by spring plunger contacts 40 mounted in arms 13, 14 carried by the plate 9. In use the neutral point of the supply is connected to the rails 38, 39 and two of the transformer tapping points, e.g. points A, B are connected, respectively, to the contact blocks 24. Initially, with the carriage in one of its extreme positions one of the tapping points, e.g. point A, is connected solidly with the neutral point and there is no connection with the point B. As the carriage commences movement a small but increasing resistance is connected in series with the point A and a large but decreasing resistance is connected in series with point B the resultant effect being that the resistance shorting the points A, B has its lowest value when the carriage is at the mid-point of its travel. At the end of the carriage travel, the situation is reversed, point B being in solid connection with the neutral point and point A being in open circuit. In modifications (not shown) the contact rollers are replaced by brushes and the blocks 25 by helical resistance wire.