GB656844A - Improvements in or relating to devices for controlling electric current circuits by means of switch elements actuated electromagnetically - Google Patents

Abstract

656,844. Electromagnetic switches; sparking preventing in switches. FKG F. KESSELRING GERATEBAU AKT.-GES. Oct. 17, 1947, No. 27881. Convention date, Oct. 18, 1946. [Class 38(v)] An electric switch having an opening time of less than one millisecond has a moving switching element which during the opening movement is subject to a main (contact closing) force, dependent on the alternating current to be switched and an auxiliary (contact opening) force which varies from an initial to a final value in a period which is greater than a half cycle. This enables the switching movement to be initiated at an instant prior to a current zero when the auxiliary force is of sufficient magnitude to overcome the main force. In Fig. 2 the switch has a combined contact and armature 11 movable by an operating member 10 against springs 15, 16. When the member 11 engages fixed contacts and poles pieces 12 13, a circuit is completed from connection C through contacts 12, 11, 13, connection B and coils 14 to connection A. The coils 14 are subsequently shorted by contacts 17, 18 as the operating member 10 moves into its final position. When the switch is opened the operating member 10 is moved to the right and the opening of the contacts 17, 18 causes the coils 14 to be energized to provide the main or holding force tending to keep the contacts 12, 11, 13 closed. As the movement of the member 10 continues, the spring 16 which was in tension is placed in compression with increasing force and overcomes the force set up by the coils 14 when the current in them approaches zero. The contacts are then opened in a time less than one millisecond. In a modification, Fig. 3, the operating member is the armature 31 of an electromagnet, the coil 34 of which is energized to close the switch 22, 21, 23. In this case, when the coil 34 is de-energized the armature 31 is pulled back by a spring 25, a dashpot 37 controlling the speed of movement. The armature 31 and pole pieces 32, 33 serve as the auxiliary switch which when opened removes a short circuit from the coil 24 enabling it to establish the main force acting on the armature and contact member 21. The opening movement of the armature 31 places the spring 26 in compression to open the switch as in the previous example. Specification 644,035, is referred to. The Specification as open to inspection under Sect. 91 also described and illustrated a switch in which normally closed contacts were opened against an A.C. holding coil by a manual operating member tensioning a spring. It also described and illustrated a mechanical contact rectifier in which contacts were opened against an A.C. holding coil by a spring periodically tensioned by a crank driven by a synchronous motor. This subject-matter does not appear in the Specification as accepted.