GB422775A - Improvements relating to electric switches for alternating current - Google Patents

Abstract

422,775. High - tension switches. SIEMENS - SCHUCKERTWERKE AKT.- GES., Siemensstadt, Berlin. Sept. 13, 1934, No. 26338. Convention date, Sept. 13, 1933. [Class 38 (v)] Sparking, preventing, and arc - rupturing devices; pneumatic actuation.-In an A.C. switch provided with means for quenching the arc at break in the fraction of a half period of the current, a switch-opening operation is commenced at a point in dependence upon the current phase, the arrangement being such that the actual separation of the contacts begins at such a time interval before a zero current passage that at the moment the current is passing through zero, the contacts are separated by a sufficient distance to prevent the re-striking of the arc. In the arrangement shown, the movable contact 4 is carried by a piston 5 and is separated from the fixed contact 3 by admitting gas under pressure through a tube 15. The pressure gas also provides a pneumatic blow-out for the arc. The opening of the switch is initiated by a valve 14 operated by a winding 17 in a control circuit 30 which includes a saturated current transformer 2, a spark gap 19 and a switch 20 controlled by an overload relay 21. On overload, high potential peaks arise in the secondary of the current transformer 2 at the zero current points and cause sparking across the gap 19; if at the same moment the overload relay has closed the switch 20, the control circuit 30 is energized and the winding 17 opens the valve 14. Owing to the overlap of the contacts 3, 4, or to a lost-motion between the contact 4 and the piston, the contacts do not actually separate until a predetermined interval after the initiation of the switching-out operation, which has taken place at a zero point of the current, and this interval is so adjusted that at the next zero after the contacts have separated, they are sufficiently far apart for the extinction of the arc. After the circuit has been interrupted at the contacts 3, 4, a switch 7 is operated by a piston 9 in a cylinder 23, to which compressed gas is admitted by a pipe 10 of small crosssection. In reclosing, the contacts 3, 4 are closed by a spring 24, and the switch 7 is then closed by admitting compressed gas to the other side of the piston 9 through a valve 12. A hand switch 22 is provided in the control circuit 30 for effecting an optional switching- out operation. For three-phase currents, each pole of the switch may be provided with a switching-out device, the phases being interrupted independently, or the arrangement may be such that only the switching-out device for the first phase to be interrupted receives the release impulse from the mains, while the switching-out devices for the remaining phases receive a release impulse from the release device of the first phase after a predetermined time.