High tension btjbbeb insulated cable
US RE21926 E
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Oct. 21, 1941. E. BORMANN HIGH TENSION RUBBER INSULATED CABLE Original Filed May 26, 1930 Reissued bet. 2 1, UNITED; STATES PATENT OFFICE i men TENSION nunnaa nvsuns'ran CABLE. Elisabeth 130mm,. Berlin-Charlottenburg, Gerslstance on the the aforementioned many, assignor' to 2 Claims.
-When manufacturing high tension, rubber insulated heavy current cables with. lead sheaths, it is not possible even in cables in which the proportion of the diameter outside oi'- the insulation to the diameter 01' the conductor is 2.72. or approximately 2.72, to prevent undue breakdown stresses in theinsulation, because it is impossible to completely avoid air and gas inclusions at the conductor and under the metal sheath, as there A are always places at which the rubber does not adhere closely to themetal, i. e, to the conductor and the lead sheath." In such gasand airinclosures within theelectric field, ionization is easily produced, through which chemical combinations takeplace, which deteriorate the insulation and are liable to be the cause or punctures of the insulation.
According to the invention th harmful influence on the gas and air inclosuresis avoided by keeping away to the desired degree the gas and aireinclosures from the electric field. It would be possible to achieve this by placing immediately on the rubber insulation a conducting layer. for
instance, in the 110m of metallized paper, tin ioil As, however, even with this measure,
owing to unavoidable irregularities in the suri'ace oi the insulation, or are liable to form through bending of the cable, it is advisable to use, instead of metal foil, rubber layers, the insulation resistance of which is reduced to a certain degree. It is (ii-advantage to make the resistance of these layers of such values to be small in comparison to the resistance, or apparent resistance. 0,! the insulation of the other rubber insulation. It is,
however, not necessary for these layers to havea considerable conductivity. Such layers, which are advantageously made essentially. of rubber mixtureadoin directly on to the other rubber so that between thelayers and the rubber insures. and no ionization can, therefore, take place. Air and gas inclusionait they occur at all, will therefore occur only between the layers ot'reduced resistance-and the conductor and between thuelayersandtheleadsheath. a
By. placing the layer of reduced insulation reconductor, one obtains. besides My invention relates to high-tension, rubber, insulated, lead-covered power cables.
or the like, such as is suggested for instance inthe U. S. Patent No. 1,199,789 to Martin Hochvstadter. small air inclosures are still liable to remain and which contain graphite; or the like. as adsulation proper there are no air-or gas-inclo- Slemens- S chuckertwerke tor is avoided Aktiengesellschait, Berlin-Siemensstadt, Germany, aeorporation of Germany Original No. 2,098,840, dated October 26, 1937, Se-
rial No. 455,662, May 26, 1930. Application ior reissue March 19, 1941, Serial No. 384,214. In Germany June 1, 1929 vantage that the increase in field intensity caused by the irregularity of the surface or the conducand that at all parts of the inner surface 0! the rubber insulation a sumciently uniform electrical stress prevails. In the draw! ing an example vention is reduced to practice. I is the conductor ofthe cable, upon which a layer 3 is placed,
the resistance of which. is small compared to that of the rubber insulation I, laid round said layer in such amanner as to prevent inclosures of air or gas. Between therubber insulation l and the sheath of the cable} a further layer i of smaller insulation resistance than insulation 4 that there are no'inis laidih such a manner closures 0! air between this layerand the rubber insulation.
The layers of reduced insulation resistance I and l, composed of rubber having, mixed with and embedded in it, particles of substancesof the class of graphite and soot, having electrical conducting properties, iorm semi-conducting layers, placed on and adapted to lie throughout inintimate contact with one or both surfaces of the rubber insulation to form with it an integral insulation to prevent ionization of gases and the layer 5 being grounded to bring the same to earth potential and conduct away the charging current of the insulation.
1 claim as my invention:
1. it high tension heavy current a condubtor, a metal sheath and rubber insulation between said conductor and said sheath, and a layer'or insulation of less resistance, adjacent to said conductor and said sheath, on each side 0t and in intimate contact with the surface oi advantage. the iurther ad- 7 the rubber insulation, having substances of electricall'y conducting properties of the class of graphite and soot admixed to and embedded in said layer to form a semi-conducting insulation. to prevent ionization of gases prevailing at the boundary between'the insulation and the conductor and sheath r tively. .2. An electhic' cable comprising a conductor surrounded-by a body or insulating rubber, and
a body of less resistance-than the said insulating rubber. composed oi rubber intermixed with conducting particles, sup rposed as a separate layer directly upon the said body of insulating rubber, in intimate contact with the entire outer surface I thereof and grounded to bring-the layer to earth potential and conduct away the charging current of the insulation. 1 V v is given by which the present incable hnvinl