GB710876A - Protective apparatus for electricity distributing systems - Google Patents

Abstract

710,876. Protective cut-out arrangements; thermal switches. CHAMBERLAIN & HOOKHAM, Ltd., DEACON, L. O., and LEWIS, H. S. April 23, 1952 [April 27, 1951], No. 9880/51. Class 38(5) A protective apparatus particularly for a polyphase system has switch elements operable by thermally-sensitive elements through differential gearing. For a three-phase system, four coiled bimetallic elements 6 ... 9 are provided, the elements being secured at their inner ends to fixed spindles 2 ... 5 and at their outer ends to gear wheels 10 ... 13 freely mounted on the spindles. The wheels 10, 12 and 13 mesh with gear wheels t, u, v which are freely mounted on a shaft a and connected to wheels b, d, f of the differential gears. The wheel 11 meshes with a gear wheel w which is fixed to the shaft a and drives wheels c, e, g of the differential gears, the wheels c, e, g also being fixed to the shaft a. Arms h, k, o arranged between the wheels of the differential gears, have pinions (not shown) meshing with the differential gear wheels and carry contacts i, m, p. The bimetallic elements 6 ... 8 are heated by coils 14 ... 16 connected in the three phases of the system and since the bimetallic coil 7 is wound in the reverse direction to the bimetallic coils 6. 8, it is only under unbalanced conditions in the phases of the system that movement of either arm h or k occurs to close the contacts i, j or m, n to effect the tripping of a circuit-breaker. In the event of overload conditions, the wheel g drives the arm o far enough for its contact p to engage an adjustably fixed contact q, the bimetal 9 through the gear wheels 13, v, f effecting ambient temperature compensation. Insofar as the operation of the apparatus under out-of-balance conditions is concerned, the bimetallic elements 6 ... 8 mutually compensate for ambient temperature variations. Heat insulating baffles 17 ... 20 effect thermal isolation of the bimetallic coils. In a modification, Fig. 2 (not shown), use of differential gearing to operate the overload contacts is obviated by connecting the outer ends of the bimetallic coils 8, 9 together and fixing the arm a to the spindle 5 which in this case is movable. The Provisional Specification describes an apparatus which differs slightly from the apparatus of Fig. 1.