Patent GB-494412-A (GB)
Title: Improvements relating to electromagnetic relay devices
IPC: H02H3/00
Filed: 1937-02-24
Abstract: 494,412. Electrically - released switches; protective cut-out arrangements. BRITISH THOMSON-HOUSTON CO., Ltd. Feb. 24, 1937, No. 5589. Convention date, Feb. 24, 1936. [Class 38 (v)] An electromagnetic relay device comprises a unidirectional magnetizing element bridged by a shunt magnetic path, having a high-reluctance portion and arranged for establishing in the shunt path a component of unidirectional flux and for producing a fringing flux in the highreluctance portion, a second magnetic path arranged in shunt to the first-mentioned magnetizing element, a second magnetizing element associated with the second path for varying the magnitude of the unidirectional flux-component and the fringing flux, and an armature arranged to be maintained by the fringing flux in juxtaposition to the shunt path and to be released therefrom when the fringing flux drops below a given value. In Fig. 3, the unidirectional magnetizing element is a permanent magnet 1 which is bridged by a shunt path 2 of large cross-section having an air gap 3 or portion of non-magnetic material constituting the high reluctance section. The second shunt path 4 is of relatively large reluctance, the latter being adjustable by non-magnetic shims 5, and is magnetized by a single conductor (not shown) gripped between the clamps 7, such that for normal current-direction in the conductor the flux in 4 tends to reinforce the flux in 2 set up by the permanent magnet, whereas for reverse currents, it tends to oppose that flux. Owing to the high flux-density in 2 and the existence of the part 3, there will be an appreciable fring- ing flux in the latter's vicinity. Since the dimensions of path 4 limit the reverse magnetization which the path may impress on the path 2, a current reversal only reduces the net flux, and hence the amount of fringing, in the latter. An armature 9 has a head 10 provided with a section t of a thickness equal to the length of path 3, whereby slight reductions in the amount of fringing flux produce release of the armature under the action of a spring 11 which is located between a flange of the armature-support 13 and a collar 12 on the armature. When released, the latter engages a contact (not shown) to effect a control, a spring-button (not shown) being provided in the housing to reset the armature. In the modification shown in Fig. 4, the shunt path 27 with which the armature 31 is associated, is separated from the permanent magnet 24 by saturable members 33 of restricted cross-section which prevent the conductor 35 from exerting an opposing M.M.F. on the magnet 24 when carrying current in the normal direction. Preferably the cross-section of members 33 is equal to that of members 34. Protective arrangements. In Fig. 5, an A.C circuit 36 supplies a D.C. circuit 37 through vapour-discharge valves 38 .. 40, the circuits of which include devices 45 .. 47 of the character described in Fig. 3, each comprising a core 48, permanent magnet 49, contacts 51, armature 50, and a coil 52 responsive to reverse current in the associated valve. The circuitbreaker 42 and indicating lamp 57 are controlled by gas-discharge valves 54 .. 56, the control electrodes 54<1> .. 56<1> of which normally receive a negative potential from the D.C. source 59 by means of resistance 60 and limiting resistances 62. The electrodes 54<1> &c. are adapted to be connected by contacts 51 to the respective cathodes in reverse-current conditions, and when a particular valve has been so rendered conductive, the voltage impressed across the others is reduced below the value required to render them conductive, so that an indication is given as to the first of the valves 38 .. 40 to experience an arc-back. If an indication only is required, the switch 68 is manually closed, and a switch 67 is opened to reset the control circuit.