Patent GB-883232-A (GB)
Title: Improvements in on-load selector switches for tapped transformers
Inventor: SCRUTTON FRANK RICHARD
IPC: H01H9/00
Filed: 1959-03-17
Abstract: 883,232. Regulating switches. FULLER ELECTRIC Ltd. March 15, 1960 [March 17, 1959], No. 9150/59. Class 38 (5). A transformer on-load tap selector switch having fixed contacts arranged in a ring comprises main and auxiliary contacts mounted on a common carrier and connected together through a resistive impedance also mounted on the carrier and carrying current only during the rotation of the main moving contact. Contact arrangement.-Fixed L-shaped brass contacts 25 (Fig. 2), are spaced at 20 degree intervals with a 40 degree gap between the two, around a synthetic resin base-plate 8. The face of each contact is protected at the edges by inserts 28 of sintered copper tungsten. The moving contacts are insulatingly mounted on a conductive wheel 21 rotated by a driven shaft 14. A pair of main contacts 23 (of which only the front one is visible) are electrically interconnected and joined by an electrical link 57 to a spoke 20 and hence to a contact ring 34 and spring-loaded contacts 39. A pair of auxiliary contacts 24, of which only the rear one is shown, are similarly interconnected and are joined by an electrical link 55 to a terminal. 54 on an insulating base 52 and hence via a resistance (not shown) to terminal 53, spoke 20 and contact ring 34. Each of the moving contacts has a sintered copper tungsten tip and is spring-urged against two locating pins 33. During the whole of its contact with a fixed contact 25, the moving contact is tilted against its spring pressure to ensure a good wiping contact in spite of wear, and as the contacts part the spring increases the rapidity of the break, to reduce arcing. The moving contacts are located in each position by three ballcatches 41 co-operating with holes in the ring contact 34.  Drive mechanism.-The contact shaft 14 is directly coupled to the shaft 72 (Fig. 5), of a Geneva wheel 76 stepped round by an operator 83 connected by helical springs 88 to a toothed wheel 81 driven via gearing and a clutch 104 by an electric motor 95. As the motor rotates the wheel 81, the Geneva wheel is locked by a spring-loaded detent 100 and hence the springs 88 are strained but the operator 83 remains stationary. As the shaft 80 rotates, a cam-lug 101a lifts the detent 100 clear and the springs 88 move the operator 83 and wheel 76 through 20 degrees with a snap-action, thus changing the transformer tapping by one step. Manual tap-changing can be effected by inserting a handle on a bifurcated shaft 92, projections on the handle being arranged to release the drive clutch 104 mechanically (Fig. 7, not shown), and break the motor circuit by means of a microswitch. Should all five springs 88 fail, a pin 112 on the toothed wheel 81 will connect with one end of an arcuate slot 113 in the Geneva operator and move the wheel 76, although without snap-action. In order to prevent a complete 360 degrees rotation of the contacts, the Geneva wheel 76 is fitted with a stop-plate 116 which also operates interlock switches which prevent further motor drive in the same direction. Should these switches fail to disconnect the motor in the limiting position, the clutch 104 is provided with shear pins which will break, and thus remove the drive. For three-phase working, three contact plates are mounted in a frame and wiped by three sets of contacts, each driven by the same Geneva wheel mechanism.