US1920180A - Electric cable - Google Patents

Description

Aug. 1, 1933.

A; P. s. BELLIS ,920,180

ELECTRIC CABLE Filed Dec. 30 1950 Y I INVENTO'R LATTORNEYE;

Patented Aug. 1, 1933 UNITED STATES ELECTRIC CABLE Alfred P. S. Bellis, Trenton, N. J., assignor to John A. Roeblings Sons Company, Trenton, N. J., a Corporation of New Jersey Application December 30, 1930. Serial No. 505,501

1 Claim.

This invention relates to concentric impregnated paper insulated cables, which now are used principally for comparatively low voltage, the object of the invention being to provide an im- 5 proved cable of this type which shall be eflicient and durable for voltages in excess of 7500 volts.

In accordance with the present invention, a special wall of insulation is provided between the two concentric conductors, this special wall consisting of the usual impregnated paper insulation with a supporting covering thereon for the layer of wires forming the outer conductor, this supporting covering preferably being formed by tapes of cotton or similar material applied in any suitable manner over the paper insulation.

For a full understanding of the invention a detailed description of a cable embodying the invention in its preferred form will now be given in connection with the accompanying drawing forming a part of this specification and the features forming the invention then be specifically pointed out in the claim.

In the drawing:

Figure 1 is a longitudinal broken elevation oi? the cable, showing the different layers;

Figure 2 is a cross section on the line 2 of Figure 1.

Referring to the drawing, A is the inner con ductor shown as formed oi the usual spirally laid cable, and B the outer conductor consisting, in the form shown, of a single layer of conducting wires arranged concentrically with the central conductor A. The cable has the usual insulating layers, a thick layer of paper 10 impregnated with insulating material next the central conductor A, a similar thick insulated layer of impregnated paper 11 outside the concentric conductor B, and the usual lead sheath 12 forming the outer wall of the cable, and in accordance with the present invention, the concentric conductor B is not laid directly upon the impregnated paper insulation 10, but upon a supporting covering formed between the paper insulation 10 and the conductor B.

This layer 13 supporting the conductor B on the paper insulation 10 may be of any suitable material, applied in any suitable manner as a serving, winding, braid or otherwise and of strength suflicient to support the outer layer of wires B and prevent these wires cutting into the paper insulation 10 and preferably of such a character that the wires B will embed themselves in the-material oi the covering 13. In practice, it

- is-found that a plurality of layers of cotton tape serves excellently for this covering 13 and such cotton tapes preferably will be used and for convenient application applied helically over the paper insulation, as shown.

The advantages of this construction include the following: The inner covering of insulated paper 10 is mechanically protected, so as to pre-' vent the wires of the conductor B embedding themselves in the paper insulation. The interstices between the wires B on the inner side will be completely or partially filled by the wires embedding themselves in the cotton, thus reducing ionization effects which otherwise might be caused by the air spaces between the wires and the insulation. The covering 13 also acts as a filler which will tend to hold within the insulation the insulating compound with which the cable is filled, and prevent this insulating compound flowing lengthwise of the cable in the openings otherwise existing between the conductor B and the paper insulation 10, especially in vertical riser cables. The dielectric characteristics of the outerinsulation 11 is not of great importance, as the outer conductor B is virtually ground poten tial in operation.

It is found in practice that the above described cable is eflicient and more durable for operating voltage of over 7500 volts and enables a much higher operating voltage to be applied across the dielectric than with previous cables.

It will be understood that the invention is not limited to the detailed construction of the cable shown, nor to the particular insulating material described, but that modifications in the construction and materials used may be made While retaining the invention defined by the claim.

What I claim is:

A concentric electric cable having a central conductor, an insulating wall of impregnated paper upon the central conductor,-an outer concentric conductor comprising a plurality of strands, each of substantially circular cross section whereby grooves or spaces exist between said strands on the inside of said outer concentric conductor, and a covering carried by the paper insulating wall and comprising a plurality of layers of cotton tape, in which the respective strands of the concentric conductor are embedded so that the outer part of said tape enters the grooves or spaces between the strands to reduce the space for ionization between said strands on the inside of the concentric conductor, said covering layer serving also as a filler to prevent the escape of impregnating or insulating compound from the paper into the spaces and the flow along said grooves or spaces between the strands.

ALFRED P. S. BELLIS.

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