Patent GB-242318-A (GB)
Title: Improvements in or relating to means for breaking electric circuits
IPC: H01H33/18
Filed: 1924-05-09
Abstract: 242,318. Whitney, W. B., Wedmore, E. B., and British Electrical & Allied Industries Research Association. May 9, 1924. Oil switches; magnetic blow-outs; fusible cut-outs. - To avoid the excessive liberation of energy produced by the extensive lengthening of an arc, an alternating current arc is quenched by keeping it as short as possible and causing relative movement in a direction perpendicular to the arc between the arc and one or both of the electrodes between which it is formed, so that when the current reaches zero in its cycle the arc has reached a cool spot and cannot restart. The apparatus is immersed in a liquid dielectric, and in all of the constructions described there is actual movement of the electrode in a direction perpendicular to the are and there is a strong localized magnetic field which acts as a barrier to prevent the arc from following the movement of the electrode. The arc therefore in general remains stationary while the electrode moves past it, but in some cases the electrode is backed with magnetic material which tends to force the arc in a direction opposite to the movement of the electrode. Figs. 1 and 2 show an oil switch having a main contact 22 and am auxiliary contact 23, which latter, when the switch-operating rod 21 is moved downwards, is engaged by a bump on the electrode 24. Further movement downwards withdraws the bump from the contact 23 and an arc is drawn between the contact 23 and the electrode 24. A magnet 28, energized by one turn from the main current-carrying lead 29 produces an intense magnet field below the arc which prevents the latter from travelling downwards. The arc, therefore, remains approximately stationary and without any undue lengthening is extinguished by being brought on to a cool portion of the electrode 24. Fig. 4 shows a modification in which an auxiliary contact 23 is caused to move rapidly away from the electrode 24 to start the arc when a projection 36 moving with the operating rod 21 engages a pin 37 and causes a toggle to collapse. Fig. 7 shows a modification in which the arc is formed between two sectors 40, each of which is pivoted to a link 41 pivoted to a bell-crank lever 42, 43 pivoted to a fixed point 44. The sectors are held in the position shown by an extension of the rod 21 engaging the arm 43 and a pin 48 on each sector. Downward movement of the rod 21 causes the sectors to separate and at the same time to rotate about their pivots. The magnet 28 as before prevents the arc from moving downwards. Fig. 10 shows a modification in which, when the switch is opened, the rod 21 not only moves downwards but also rotates, and carries a disc 20 which engages and then passes auxiliary contacts 24 till it reaches the dotted line position, when arcs between the contacts 24 and the edge of the disc 20 are prevented from following the rotation of the disc by the strong magnetic fields between the poles 27 of the magnet and a magnetic member 52 on the axis 21. Fig. 12 shows the application of the invention to a fusible cutout. When the fuse 63 blows, levers 61 pivoted at 62 are released, and their upper ends escape from members 65 so that rectangular frameworks 60 are forced downwards. The arc is caught on to arcing horns 67 forming part of the frameworks, and is prevented from moving downwards by the field produced by the magnet 27. Specifications 17712/13, 118,536, 170,148, 175,969, and 194,273 are referred to.