Patent GB-190820590-A (GB)
Filed: 1908-09-30
Granted: 1909-09-30
Abstract: 20,590. Fisher, H. J., Coates, F., Clothier, H. W., and Reyrolle & Co., A. Sept. 30. Switches; cut-outs.-An enclosed switch arrangement for use in safety mining and like systems is operated electro-magnetically by a control switch through mechanism adapted to lessen the power required to maintain the switch closed, whereby an electro-magnet smaller than the operating electromagnet may be employed as a retaining-magnet, the circuit controlled being completed through a plug interlocked with the control switch ; a lamp is provided to indicate when the supply side of the main switch is alive, and'overload arrangements with a time-limit device are employed. The electro-magnet plunger g, Fig. 1, is pivoted to a lever e. which has a lost-motion connexion at h with a lever d jointed to the moving element a of the switch and pivoted at f. The lever e is provided with a slot e<1>, in which moves a roller k connected by a spring to a fixed point j. As the plunger rises to close the switch, the lost motion of the pin in the slot h is first taken up, then the spring i is extended until the direction of inclination of the slot e' is reversed, when the roller moves and the spring operates at the other side of the pivot f so as to maintain the switch closed, but with a force less than that which formerly kept it open because of the lesser leverage of the spring about the pivot f. When the magnet is de-energized, the weight of the plunger &c. is sufficient to reverse the inclination of the slot and to bring the spring i into operation to produce a rapid break. The switch may be fitted in an explosion-proof box. As employed in a three-phase supply system, three pairs of stationary contacts c, Fig. 5, are supported by insulators c<1> within the lower part of a box containing oil. The movable element consists of three bridging pieces carried by the mechanism described above. The cover of the box surmounts two sockets, one n<2> containing the supply cables, and the other containing, for example, five plugs p<1> ... p<5>, Fig. 8, adapted to enter holes q<1> ... q<5> in the hollow extremity of a removable plug which ia fitted to a cable leading to the motor to be supplied. The electro-magnet has an operating-winding b<1>, Fig. 9, and a smaller maintaining-winding b<2>. The connexions, arranged to prevent the switch being closed unless the motor is efficiently earthed, are as follows :-The winding b<1> is connected from one of the phases through switches s<4>, w<3> to the plug and socket p<4>, q<4> and to the framework of the motor. A second conductor is connected through the plug and socket p<5>, q<5> to the framework of the switch. To change over from the coil b<1> to b<2>, a switch s<2>, Fig. 5, is employed consisting of two spring contacts u, u<1> electrically connected in a casing mounted so as to be revolved by an external handle so that the axial contact u always engages the contact t, while the contact u<1> engages one of two contacts, of which one, t<2>, is shown. A crank and spring arrangement causes the switch to take up one or other of the two positions, and a spring-pressed ball detent may be employed to determine these positions. The handle is provided with a lug s<5>, which engages, when the switch is in the 'on' position, under a lever pivoted to the switch casing ; the other end of the lever engages with the plug casing so that the latter cannot be removed while the switch is ' on.' Overload releases may be employed consisting of electro-magnet cores x, Fig. 5, actuated by a few turns of the circuit wires and adapted in their upward movement to raise contacts w upon a pivoted plate, Fig. 9, which bridge two stationary contacts w<3> in the circuit of the operating and retaining coils. The plungers x slide in guides x<2> over which slides a sleeve x<3>, which acts as a cylinder for a piston x<5> carried by the plunger x. The oil of the switch box has free access to the cylinder, and, by employing valve-controlled passages through the piston, the upward movement of plungers may be resisted for a portion of their travel. The sleeves x<3> may be pivoted to a carrier so that they may be adjusted together. A lamp z connected across one of the phases is arranged behind a window in the switch box and serves to indicate that the supply side is alive ; the plunger g may be provided with an extension which interposes a shutter between the lamp and the inspection opening.