Patent GB-536281-A (GB)
Title: Improvements in and relating to electromagnetic apparatus
IPC: H01H51/01
Filed: 1939-12-30
Abstract: 536,281. Automatic circuit-breakers ; oil-blast switches. BRITISH THOMSON-HOUSTON CO., Ltd. Dec. 30, 1939. No. 33100. Convention date, Dec. 31, 1938. [Class 38 (v)] [Also in Group XXXV] The contact 20 is moved into engagement with the contact 18 by a coil 1 which is then deenergized and the contact retained closed' by a permanent magnet, tripping being effected either by reversely energizing the coil 1 or by energizing a trip coil 11, which may be interleaved with the coil 1 but, as shown, is located adjacent the armature 4. The permanent magnet is a cylinder 9 of the alloy described in Specifications 423.897 and 424,746, [both in Group II], and the structure includes magnetic discs 2, 3, the former co-operating with a flange 4<1> and the latter having a hub 3' cooperating with the main part of the armature. The rod 5 of insulating or non-magnetic material passes through the hub and through a cylinder 7 containing a throw-off spring 6, and carries a piston 24 which, in opening, drives oil through port 27, across the arc, and out of vent 29. The armature provides two separate holding surfaces, namely, between 2, 4<1> and 3<1>, 4, and when the breaker is tripped, a reverse flux sufficiently neutralizing the holding flux is passed across the surfaces 2, 4<1>, so shifting the holding flux to the outside of the coil 11, which is of the character described in Specification 500,472. Movement of the armature is accelerated, after a small initial separation of surface 4<1>, owing to the flux being diverted so as to enter the main armature 4 normal to the line of movement of the latter, a fibre cylinder 12 being interposed in this gap. The trip coil can be reversely energized in parallel with 1 for closing purposes. In Fig. 2 (not shown), the tripping speed is increased by placing the coil in a small pot-magnet the base of which is secured to the hub 3<1>, and by providing disc 2 with a seating for the part 4<1> in closed position, so reducing the reluctance of the tripping-flux path. The arrangement can be automatically reclosed by reversely energizing coil 1 to produce an opposing flux in the part 4<1>, the spring 6 overcoming the holding flux while the reverse current is building up in coil 1. When the coil-current is adequate, the reverse current arrests the armature and then retracts it, so reclosing the contact, which is again held by the permanent magnet, when the coil-current is cut off. The same cycle can be performed by energizing the coil 11, 1 in that order, but the method is slower. The coil 1 may be energized from an a.c. source over a full-wave rectifier, and may be arranged in two parts in series or parallel according to the voltage, the coil parts. when in parallel, being interleaved and of the same characteristics. In a modification, Fig. 3 (not shown), the permanent magnet is in the form of a disc secured beneath the disc 2 and separated by a steel disc from the armature, the flange of which co-operates with the under side of disc 3. In this form a trip coil is provided for each holding surface and a modified form of blast-delivery to the contacts is provided. In all these forms, the permanent magnet is recharged at each energization of coil 1 and the action is intensified by the impact of the armature on the fixed structure. Fig. 6 shows a trip-free form employing two armatures 48, 49, urged apart by the spring 6, the armature 48 being normally anchored, but releasable by a trip coil 36 when closing on to a fault. Armature 48 is secured to a rod carrying a hollow blast contact 68 and armature 49 carries a contact 69 which is movable for closing and normal tripping under the action of coils 1, 37, respectively. The coil 73 restores the armature 48 to its anchored position where it is retained by the disc permanent magnet Ml. Armature 49 is retained by the disc permanent magnet M2, a steel plate 60 being provided with niches 60<1> to produce saturation and so cause the flux of coil 1 to assist magnet M1 inretaining armature 48. A port 70<1> in the hollow rod. 70 above piston 65 admits blast fluid from cylinder 67 to the nozzle-contact 68, a blast taking place on relative movement between the piston and cylinder, that is, even if the armature 48 ds released when the armature 49 is still rising. Fig. 5 (not shown) illustrates a trip-free form employing two armatures and a single coil 1 in a cylindrical permanent magnet. In Fig. 7, the pole pieces 2 and armature 74 have annular insulating gaps 80, 77, respectively, the armature parts being secured to an insulating plate 78. The arrangement provides an increased holding force due to the four holding surfaces. The device can be calibrated for sensitivity by making the armature-ring 76 and pole-ring 83 in the form of alternate steel and insulating sections, and by rotatung the armature as a whole to stagger the steel sections to a varying degree, Fig. 8 (not shown).