Patent GB-613396-A (GB)
Title: Improvements in electric cut-outs particularly for the protection of motors against faults or overload
IPC: H01H83/14
Filed: 1946-06-20
Abstract: 613,396. Protective cut-out arrangements; automatic circuit-breakers. MAYER, V. June 20, 1946, No. 18531. [Class 38 (v)] In a protective device for polyphase apparatus, the armatures 1a ... 1c of electromagnets 2a ... 2c connected in each phase are coupled to a lever system, which can be moved on the occurrence of balanced overload or unbalanced circuit conditions, to actuate a pivoted bar 9 and open a switch 11. In a threephase arrangement, Fig. 5, armatures 1a, 1b are attached to the ends of a lever 4, pivoted at its centre on one end of a lever 5, which has an armature 1c and is pivoted at one-third of its length from the pivot of the lever 4, on a forked-arm 6. The arm 6 is itself pivoted at 7 to the frame of the device, and presses up-. wards against a stop 8 with a force F2. The bar 9, which is cranked, is mounted in fixed pivots 10 and presses upwards on the underside of the levers 4, 5 with a force F1 normally holding the armatures 1a ... 1c out of their coils 2a ... 2c at the same level. On balanced overload, the armatures are drawn down into their coils, overcoming the forces F1, F2, and carrying the levers 4, 5, bar 9 and arm 6 downwards, to open the switch 11. 'In the. event of a break in one phase, however, the armatures associated with the other phases will be drawn into their coils, tilting the lever-system and forcing the bar 9 downwardly to open the switch 11, the arm 6 remaining against its stop 8. The forces F1, F2 are adjustable to vary the unbalanced and balanced tripping currents respectively. In a two-phase arrangement, Figs. 1-4 (not shown), a single lever with an armature at each end is pivoted at its centre on the ends of the forked-arm. The forces F1, F2 may be supplied by springs or counterbalance weights, or as shown in Figs. 11, 12, 16, both forces may be supplied by a single balance-weight 20, mounted on a lever 19 pivoted to the frame 33 at 7, and connected by means of a link 19a to one arm 18 of a pivotedlever, the other arm 16 of which carries a lever 15 in a V-notch. The lever 15 is connected to the bar 9 and arm 6 by links and is so proportioned as to give the desired ratio of forces F1, F2, the arm 18 being adjustable on the arm 16 so as to vary these forces and therefore the tripping current. The lever 19 may be connected to a time-lag device, such as the piston of an oil dash-pot 13, to prevent tripping on momentary current fluctuations, and the dashpot cylinder may be held down by an adjustable spring 22 so as to move bodily on heavy overloads. The dash-pot may be compensated for variations in the viscosity of the oil with temperature variations, by a valve-disc 30, movable by a bimetal helix 31 to uncover an aperture in the piston. The switch 11 comprises a contact 12, loaded by a spring 12a, and normally held against a fixed contact 11a by an insulating-roller 25 on a cranked wire 26 pivoted to the frame 33 and latched by a lever 27. When the lever 9 is depressed, it engages the tail of the lever 27 and allows the contacts to separate under the action of the spring 12a. The switch may alternatively be unlatched on .heavy overload, by the end 19b of the lever 19. To prevent the switch being tripped by a slightly unbalanced load immediately following a temporary balanced overload, in which conditions the force on the arm 6 is temporarily relaxed due to the relatively slow return of the dash-pot piston, a catch pivoted on the arm 6 is adapted to engage a peg on the lever 9 and hold the latter.