US1665191A - High-tension cable to prevent a breaking down of the insulation - Google Patents

Description

April 3, 192a. 1,665,191

E. G. SIEVERT ET AL HIGH TENSION CABLE TO PREVENT A BREAKING DOWN OF THE INSULATION Filed NOV. 9, 1925 a. 5M W Patented Apr. 3, 1928.

UNITED STATES PATENT OFFICE.

ERNST GUSTAV SIEVEBT AND HENNING SVE NSSON, OF SUNDBYBERG, NEAR STOCK- HOLE, SWEDEN.

HIGH-TENSION CABLE TO PREVENT A BREAKING DOWN OF THE INSULATION.

Application filed November 9, 1925, Serial No. 67,949, and in Sweden November 20, 1924.

The present invention refers to an improvement in high-tension cables to prevent a breaking-down of the insulating layer.

Such a breaking-downwill generally take place in suchpoints of the cable, in which the insulating power ofthe layer has been reduced, for instance by a somewhat less thickness, already at the manufacture, or has got any other unintentional reduction of the specific electric insulating power of the insulatin material. If a puncture has once happened in some point of. the insulating layer the cable will be Very rapidly destroyed as the puncture is combined with chemical as well as thermal processes which exert influence upon adjacent parts of the insulating material and which will gradually cause a .total breaking-down between the very conductor of the cable and the earth.

According to this invention, in order to remove this source of disturbances, one or more layers of an insulating material, having an electric insulating power inferior to the remaining insulating material, are applied 2 into the insulating layers of the cable.

This arrangement efi'ects an equalizing of the tension, by which fact the causes of the initiating of the partial puncture are removed or at least, essentially reduced. It is evident that the equalizing tension will be the better and more complete thelower the electric insulating ower of the equalizing layer is. On the ot er handa reduction of the specific electric insulating power of said venience or danger depending upon the fact that if the electric insulating power of the layers is made too small, two partial unctures possibly produced, in spite oi the equalizlng layers, at a distance from one another counting in the longitudinal direction of the cable, may add so thatthe result will'be inferior to that obtained without any equalizing layer or layers. The electric insulating power of the equalizing layers should, on account of this, accordin to the invention, also be chosen with regar to the probable distance between weakened points, favorin the arising of partial puncture, of the ins ating material in a well made cable,

equalizing layers involves another incon-v a weakened point 10, the tension will -maintain the maximum potential difference between two breaking-down points l0cated"65 in the equalizing layer, provided these points are not located at a shorter axial distance than the probable minimum distance supposed in advance, which, as already indicated above, is different for diiferent cablb structures. As insulating materials for the equalizing layers, a plurality of "difi'erent materials, known per se, may, of course, be used, for instance asbestos, which material has proven to be particularly suitable.

The annexed drawing shows, diagrammatically, an embodiment of a cable according to the present invention, in longitudinal section.

1 is the lead sheath, 2, 3, 4, 5 the several layers of insulating material, 6, 7, 8, 12 the equalizing layers' placed between the former and 9 the electric conductor.

If, for instance, the insulating layer 2 at the outside, when manufactured, has got 1ncrease at this point, but on the other hand the equalizing layer 6 tends to reduce the tension and equalize it so as to reduce the danger of a breaking down. In the same 99 manner the increasing of tension, due to 'a ossible weak point 11 in the insulating. ayer 3, is equalized. If, in spite of this, the points 10 and 11 should be punctured, these unctures are, however, prevented from addmg by the relatively low electric insulating power of the equalizing layer 6, said equalizmg layer preventing (the example chosen being still considered), the voltage drop produced in thepoint 10 from being transmitted to the point 11, which is supposed to ed, between adjacent weakened points in the insulating layers 2 and 3.

Having now particularly described the nature of our invention and the manner of its operation, What we claim is:

A high-tension cable including an insulat- 10 In testimony whereof we herewith aflix 15 our signatures.

ERNST GUSTAV SIEVERT.

HENNING SVENSSON.

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