GB423967A - Improvements in or relating to electricity meters - Google Patents

Abstract

423,967. Electromagnetic and thermal switches. HARWOOD, H. V., 53, Sutherland Road, Chorlton-cum-Hardy, Manchester, and ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Crown House, Aldwych, London. Nov. 27, 1933, No. 33208. [Class 38 (v)] [See also Group XXXVI] Two-part tariff meters with relay connections causing a load smaller than a predetermined value to be metered at the higher rate and a load above the predetermined value at the lower rate have a thermal relay heated by the load current, the rate changeover being effected through a pair of electromagnets which disconnect and connect either the high or low-rate meter coil. The thermal relay may be a bimetallic strip which itself effects the closing of one or other of the electromagnets. Means are also provided for alternately opening and preparing the circuits of the electromagnets. The meter current coils 2, 3 have the numbers of their winding turns in the ratio of the respective tariff prices. A single meter with two current coils, as shown, or two separate meters, or a tapped current coil may be employed. The electromagnets 21, 22 actuate a tilting mercury switch 5 when energized through contacts 8, 10 or 9, 11 in dependence upon the load current passed by the heating coil 6, overheating of the coil 6 being prevented by shortcircuiting it through contacts 14, 15 made when the bimetallic strip 7 flexes beyond normal requirements. The common terminal 5a of the mercury switch is connected to the heating coil and the end terminals C<1>, C<2>, to the meter coils 2, 3. The frame on which the mercury switch is carried is rocked by the plungers of the electromagnets 21, 22, the arrangement being such that when the mercury switch is thrown for metering on one tariff one of the pairs of contacts 25, 26 or 29, 30 is closed to prepare the circuit for metering on the other tariff. The construction of the mercury switch is shown in Fig. 2, the magnet plungers 48, 49 rocking the frame 31 which reciprocates a rod 34 carrying silver sleeves 42, 43 and insulating parts 40, 41. Springs 46, 47 locate the switch in its tilted positions. The thermal relay includes a mirror 52 for reflecting the heat on to the bimetallic strip 7. Compensation for temperature changes may be effected by carrying the contacts 10, 11 on opposite arms of a U-shape member 56, Fig. 4, mounted on a second bimetallic strip 51 arranged parallel to the strip 7 but on the opposite side of the heating coil 6 and screened therefrom by the mirror 52. The short circuit produced by contacts 14, 15 is then made by a pin 54 carried on a third bimetallic strip 53 mounted on the post 7a with the relay strip 7.