US3172073A - Resistors - Google Patents

Description

March 2,1965 5. BOLTON am 3,192,073

RESISTORS Filed March 30, 1962 31 26 1B 32 32 FIG.1

I I I L I E 19 I 20 E United States Patent 3,172,073 RESISTORS Eric Bolton, Marian Kazimierz Ancilewski, and John Hewitt, all of Stafford, England, assignors to The English Electric Company Limited, London, England, a

British company Filed Mar. 30, 1962, Ser. No. 183,827 1 Claim. (Cl. 338-280) This invention relates to resistors such as are used for example in parallel with the contacts of circuit-breakers used for high power high voltage applications.

In heavy duty alternating current switchgear including circuit-breakers, it is usual to provide a resistor in parallel with the main contacts, and the final interruption of the circuit may be achieved by opening of contacts in series with the resistor, these contacts operating at lower current values than would be main contacts in the absence of such a resistor.

The contacts in series with the resistor are in one arrangement also in parallel with the main contacts, in which case the main interrupter contacts alone carry the full fault current and the contacts in series with the resistor carry the resistance current after the main contacts have opened, until these contacts themselves open; in another known arrangement, the series contacts are in series both with the resistor and with the main contacts, the latter being in parallel with one another; in this case both the main interrupter and the series interrupter carry the full fault current until the main interrupter opens, when the current drops so that the series interrupter then only carries the current flowing through the resistor.

The thermal capacity of the resistor is of prime importance since there is little time available for heat to be conducted or radiated away. The resistor in accordance with the invention has the advantages of high thermal capacity combined with compactness, together with high electrical strength and low inductance.

One embodiment of resistor in accordance with the invention will now be described with reference to the accompanying drawings of which:

FIG. 1 shows a transverse section through the resistor; and

FIG. 2 shows a section on the line 22 of FIG. 1.

The resistor forms part of a 132 kv. air-blast circuitbreaker and is connected to be electrically in parallel with the main contacts of the circuit-breaker.

The resistor comprises a strip 11 of high-resistance metallic material such as Nichrome (registered trademark) which is folded in a multiplicity of convolutions, adjacent convolutions being separated by strips 12 of insulating material such as mica. There may, for example, be approximately 2,000 such convolutions. Held against the end convolutions of the metallic strip are oppositelydirected T- shaped parts 13, 14 of a material of good thermal and electrical conductivity such as copper. The strip 11 is secured to the T-shaped parts 13, 14 by means of clamping plates secured by screws. The part 13 is formed with a flange 15 and has its stem portion received in an aperture 16 in an end housing member 17 which may be of mild steel. The housing member 17 together with the corresponding member 18 at the other end of the rseistor assembly form part of the electric circuit in paallel with the main contacts of the switchgear (not shown) and in order to ensure good electrical contact between the strip element 11 of the resistor and the end housing member 17, the aperture 16 is formed with a groove 19 containing a garter spring 20 which surrounds the stern of part 13.

The end housing members 17 and 18 are spaced apart by a ribbed hollow bushing 21 of porcelain or similar material to which they are secured in conventional manner by clamping rings 22, 23 and set screws 24, 25.

The part 14 has its stem slidably mounted in an aperture 26 in the end housing member 18, the latter being formed with an annular groove 27 containing a garter spring 28 which surrounds the stem and ensures good electrical contact between the part 14 and the end housing member 18. The part 14 is formed at its end with a flange 29 which abuts the end convolution of the strip 11 through a conducting block, the strip 11 being held in compression between the flanges 15 and 29 by means of a coil spring 30 which is placed in compression between the flange 29 and an end beam 31.

The flange 15 forms a corresponding end beam at the other end of the resistor assembly, and the two end beams 15, 31 are connected by two bolts 32 of insulating material, for example of porcelain or a suitable ceramic, which are in tension. The compressive force applied to the assembly of the convoluted strip 11 and the mica strips 12 may be determined by the dimensions of the spring 30 and may be of the order of pounds.

The strip 11 should be of uniform cross section so that the current density is uniform and localized heating is avoided.

It will be appreciated that current flows between the end housing members 17 and 18 through the T- shaped parts 13, 14 and the strip 11. The assembly, including the convoluted strip 11, mica strips 12, end beam members 15, 31, and bolts 32 may readily be inserted within the bushing 21 by removal of one of the end housing members 17, 18.

The resistor is capable of operation in air or inert gas and may also be used submerged in oil, though in the latter case the temperature which can be withstood is unlikely to be as high as when suitable gas is used. The bushing may alternatively be filled with dry fused bubble alumina in air.

The invention provides a high-voltage resistor assembly of compact dimensions which can withstand high temperatures. It has been found that temperatures calculated to be of the order of 1,000 C. have been generated over a short period without ill effect.

What we claim as our invention and desire to secure by Letters Patent is:

A resistor comprising an assembly including a thin elongated member of high-resistance metallic material formed into a multiplicity of convolutions, temperatureresistant electrically insulating material filling the spaces between the convolutions, a pair of transverse flanges, one at each end of said assembly, an end beam substantially parallel to and spaced from one said transverse flange, a compression spring compressed between said end beam and said one transverse flange, and at least one tension member of electrically-insulating material joining said end beam and the other said transverse flange, whereby said thin elongated member is held in compression between said transverse flanges, said resistor also comprising a pair of apertured electrically-conducting end housing members and an electrically-insulating bushing spacing apart said members, and said assembly comprising oppositely-directed stem portions formed one on each of said transverse flanges and engaging in the apertures in the respective end housing members.

(References on following page) 3 References Cited in the file of this patent 621,561

UNITED STATES PATENTS 497,366 Wright May 16, 1893 515,280 Brown Feb. 20, 1894 5 534,699 Shaw Feb. 26, 1895 177,399

Freeman Mar. 21, 1899 Steerup May 7, 1929 Bocciarelli Feb. 20, 1951 FOREIGN PATENTS Great Britain Mar. 30, 1922

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