GB619343A - Improvements in and relating to electric switches having arcing contacts - Google Patents

Abstract

619,343. High-tension switches. BRITISH THOMSON-HOUSTON CO., Ltd. Dec. 3, 1946, No. 35815. Convention date, Dec. 4, 1945. [Class 38 (v)] A switch suitable for disconnecting small currents such as the magnetizing current of a power transformer 2 has arcing contacts 17, 18 in an evacuated envelope 16 which are connected in circuit before the main fixed and moving contacts 10, 11 break, and are separated afterwards to take the arc. The switch housing 6 may contain a liquid insulating dielectric as disclosed in Specification 601,572, [Group XXXVI], and pivotally supports at 12 the main contact 11 having a contact ring 13 engaged by fingers 14. The movable arcing contact 18 is mounted on a conducting rod 20 piercing a thin metallic diaphragm 21 whereby it is spring-biassed to the closed position. A pivoted lever 25 electrically connected to the rod 20 is held by a spring 29 in a mid-position with the arm 27 normally spaced from the end 22 of the rod. A conducting cam surface 32 on an insulating support 31 is connected to the fixed main contact 10. As the contact 11 moves counterclockwise to open the switch, the end 26 of the lever 25 engages the cam surface 32 and completes a shunt circuit to the contacts 10, 11 which then separate. Further movement causes a depending portion 33 of the cam surface to rotate the lever 25 clockwise, and the arm 27 moves the rod 20 to open the arcing contacts 17, 18. On closure of the switch, the lever 25 is rotated counterclockwise by the insulating support 31, whereby the shunt circuit through the cam surface 32 is not completed until the main contacts 10, 11 have engaged and taken the high inrush current, thereby avoiding damage to the contacts 17, 18 by transformer-inrush currents.