An improved apparatus for protecting electrical apparatus against overload

Abstract

Abstract 553,154. Electrically-released switches. ELECTRICAL APPARATUS CO., Ltd., BURKE, J. N., WALTON, J. R., and WATTS, T. H. July 24, 1942, No. 10408. [Class 38 (v)] In a device comprising a plurality of currentsensitive members each responsive to one of the currents between which unbalance is to be avoided, and an operative connection between the members and a switch, whereby the latter is operated by excessive uniform movement of the members on overload and by non-uniform movement of the members on unbalance, there is provided, in addition to the normal calibrating member, means for preventing the device being set by manipulation of the calibrating member to a load higher that the maximum intended. In a three-phase application, an insulating base 10 is provided with heat-insulating ribs 12 .. 14 forming compartments receiving bimetal elements 19 in series with heating coils 22 and arranged to deflect to the right, Fig. 7. The upper, free ends of the strips 19 engage slots 25, 26 in a pair of sliding plates 27, 28, the plate 28 having pivoted to it at 29 a bell-crank lever 30, one arm of which carries a pin 31 taking in a hole in plate 27 whereas the other arm carries a roller 32 engaging a movable contact strip 33, Fig. 2. The strip 33 pivots in a hole in a bracket 35 and is urged by a spring 37 in a direction such that its upper end presses on roller 32 and a hook 38 engages over a co-operating contact 39. Normally, therefore, plate 28 is moved by the strips 19 and owing to the restraint imparted by contact-strip 33, the lever 30 causes plate 27 to follow it. If the plate 27 lags, however, lever 30 rotates and roller 32 presses back strip 33 and contact 39 flies up under the action of spring 43 and opens the circuit of, for example, a contactor, Fig. 8. The lag may be due to unbalance causing one or more strips 19 to flex less than the others. Overload protection causing excessive uniform deflection is, however, also caused to impart relative movement to plates 27, 28. For this purpose, a compensating strip 46 is mounted on a bracket 44 pivoted at 45 and is adapted to engage the plate 27. The value of overload is predetermined by a calibrating member 49 pivoted at 50 and having a pointer 51 moving over a scale 52. At the given overload the extension 48 of bracket 44 is stopped by the member 49 so arresting plate 27, whereby continued deflection of the strips separates contacts 38, 39. To prevent excessive movement of member 49, Fig. 7, a stop may be provided, or, alternatively, a stop may be adapted to arrest plate 27 to produce unbalance. Preferably,.however, an unbalance is effected by shaping the. barriers 12 . . 14 so as to limit the movement of strips 19, to an uneven degree, the right-hand strip being allowed the greater movement. A resetting button is provided for the contact 39, Fig. 6 (not shown). The heating coils may be transformer-energized from the respective lines and the invention is applicable also to singlephase and direct-current circuits.

Inventors

No inventors recorded.

Bibliographic Details