GB562701A - Improvements in or relating to electric resistors - Google Patents

Abstract

562,701. Grid resistances. REYROLLE &, CO., Ltd., A., MORDUE, H., and MILLER, A. R. Jan. 7, 1943, No. 345. [Class 37] A resistor for use on heavy power circuits comprises one or more units each consisting of an element formed of a strip of expanded metal bent in flat zig-zag formation, or a plurality of such strips connected together at alternate ends to form a flat zig-zag, and so as to be in intimate contact with a material which has good heat absorption characteristics and affords yielding support for the element. Each unit consists of a concrete casing, constituted by a base B, in the shape of rectangular flat dish with trans: verse ribs B<1> projecting upwardly within it, and a flat concrete cover B<2>. Loose concrete blocks C' are disposed beneath the cover B<2> opposite to the ribs B<1> and spaced from the ribs by the width of the metal strip C from which the resistance element is formed. Each resistor C is formed of a strip of expanded metal bent into zig-zag formation so that each turn is supported by its edges between the ribs B<1> and blocks C<1>. The whole space within the casing is filled with sand or other granular, powdered, or fibrous heat absorptive material. The ends of the element C are connected to terminal tabs C<3> extending through recesses between the base B and the cover B<2>, the tabs being held in position by bolts C<4> embedded in the concrete of the base B. The joint between the cover and the base is sealed by a soft weatherproof sealing composition D. A number of separate lengths of expanded metal may be joined at alternate ends or otherwise interconnected to form a network. A number of units are assembled one above another to form a stack, the base B being provided with feet. B<3> so that its lower surface is slightly spaced above the cover B<2> of the next lower unit. The resistor elements in a stack are connected in series by interconnecting straps. Several such stacks may be connected in series, parallel, or series-parallel, between the neutral point of a supply system and earth-.in order to carry large neutral currents during earth fault conditions. A separate cover for each unit may be dispensed with, except at the top of a stack, the base of one unit being shaped to fit on top of the next lower unit with a weatherproof joint.