US2067170A - Electric cable - Google Patents

Electric cable Download PDF

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Publication number
US2067170A
US2067170A US685192A US68519233A US2067170A US 2067170 A US2067170 A US 2067170A US 685192 A US685192 A US 685192A US 68519233 A US68519233 A US 68519233A US 2067170 A US2067170 A US 2067170A
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United States
Prior art keywords
spaces
paper
gas
conductor
cable
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Expired - Lifetime
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US685192A
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English (en)
Inventor
Beaver Charles James
Davey Edward Leslie
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WT Glover and Co Ltd
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WT Glover and Co Ltd
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Filing date
Publication date
Application filed by WT Glover and Co Ltd filed Critical WT Glover and Co Ltd
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Publication of US2067170A publication Critical patent/US2067170A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B9/00—Power cables
    • H01B9/06—Gas-pressure cables; Oil-pressure cables; Cables for use in conduits under fluid pressure
    • H01B9/0644—Features relating to the dielectric of gas-pressure cables
    • H01B9/0655—Helically wrapped insulation

Definitions

  • the residual air or gas 20 is usually finely divided and uniformly distributed as very small bubbles or in solution in the impregnating compound of the dielectric when the cable is newly made, and the dimensions of the occlusions are such that the gas is not ionizable until much higher stresses than those corresponding to the working voltage have been applied, the said dimensions are liable to become altered by aggregation after the cable has been heated, so that ionization may then occur at 30 lower stresses.
  • anew combination of conditions within the cable is provided.
  • One of the conditions is that spaces of definite and substantially invariable dimensions are provided for the gas present in the cable.
  • the other condition is that the gas is continuously maintained under a pressure substantially below atmospheric pres- 1933, Serial No. 685,192 September 27, 1932 sure. It is well known that for each thickness of gas layer the ionization voltage falls continuously as the pressure of the gas is reduced until a critical pressure (hereinafter called the criticalv value) is reached; below this pressure the ionization voltage rises rapidly.
  • the pressure in the present case is made so low, having regard to the dimensions of the spaces, that the gas therein will not. be ionizable in the conditions under which the cable will work.
  • This pressure is ad- 10 justed to be below the critical value for the largest radial dimension of any of the gas spaces in the cable so as to take advantage of the relatively high ionizationV voltage obtained in that region.
  • the dimensions of the spaces are assured by forming the spaces in the process of lappingv on the paper layers so that they are determined radially by the thickness of the paper, and longitudinally by the spacing of the lappings in each layer. Where impregnated paper is vto be used steps are taken to provide that the spaces between the lappings of paper are substantially clear of free compound, that is the compound is vretained. in the paper and on its surface.
  • impregnated paper for use in the manufacture of a cable in accordance with the present invention it is impregnated before application to the conductor with a compound hav-l ing such a setting point as to ensure that physical stability of the impregnated paper is maintained up to a temperature well above the maximum 40 reached in the working conditions of the cable.
  • the impregnation may, for instance, be carried out as set out in the speciiication of U. S. Patent 1,752,972 or of U. S. Patent No. 1,958,984.
  • the paper may be provided ⁇ with a lubricating film as described in the said specifications.
  • This film is preferably applied to one side of the paper Aonly and is of very small thickness. It may, for instance, consist of a coating of petroleum jelly having a. high viscosity and set point.
  • the conductor I is covered with a thin metal tape or foil 2 and is lapped with layers or lamlnae of paper strip indicated by the refer- Over the outside of this dielectric material is placed a metallized layer 6 (preferably perforated) and over this the lead sheath l is applied. To the outside of the lead sheath is applied a metal reinforcing tape 8 and this is protected in the usual way by layers of impregnated fabric 9.
  • the metal tape 2, the metallized paper 6, the reinforcing tape 8 and the fabric layers 9 will as usual be lapped on helically. No attempt has been made to show this in the drawing.
  • the thin metal tape 2 lapped on the conductor I, performs the known function of reducing local intensities of electric stress and also gives a definite inner cylindrical surface to the di electric layer.
  • the desired results can be obtained by forming (either before or after stranding) the component wires of the outermost layer of the conductor in such a way as to give a smooth outer surface to the conductor.
  • a thin lead tube covering the conductor as a whole may be used as described in the specification of U. S. Patent No. 1,256,863.
  • the strips of the paper are lapped on the cable in air which isI 5 preferably kept below normal humidity and the cable is then sheathed with lead or lead alloy, to which reinforcement may be applied as protection against external influences.
  • the air enclosed in the dielectric which is chiefly located l0 in the spaces provided between the turns of paper, together with the other air in the cable, is evacuated to the desired extent. It may be replaced by an inert gas, such as nitrogen, carbon dioxide, helium, neon or other suitable gas.
  • the l5 process of removal of air and filling with gas may be facilitated by a repeated flooding and exhausting of the gas into and from the cable and by the application of heat to the cable intermittently or continuously, either by external means or by the passage of current through the conductor or conductors or by both of these.
  • the final step in all cases is to evacuate the cable to obtain the dedesired low pressure, the cable having been sealed at the ends in order to prevent leakage inward.
  • the choice of the radial dimensions of the gas spaces and of the gas pressure will depend upon a number of conditions. It will however generally be advantageous to make the gas spaces at the surface of the conductor of small radial 3U dimensions, for instance, one and a half thousandths of an inch. By increasing the thickness of the layers or wrappings of paper from the conductor outwards, the radial dimensions of the gas spaces may also be increased, taking advantage 35 of the fact that the intensity of electric stress decreases from the surface of the conductor outwards. With such dimensions and with an absolute pressure of the order of 0-10 millimetres of mercury, conditions can be obtained which per mit a very high voltage to be applied without obtaining ionization. It will be understood that the figures given are only by way of example.
  • An electric power cable comprising a conductor, an enclosing sheath and a laminated dielectric layer between the conductor and the sheath, said dielectric having spaces of predetermined dimensions and positions distributed through the laminations, these spaces having a radial depth which increases from the conductor outwards, and gas in these spaces at a pressure less than thecritical value for the largest radial dimension of any of said spaces.
  • An electric power cable comprising a conductor, an enclosing sheath and a laminated dielectric layer between the conductor and the sheath, said dielectric having spaced apart interstices in the laminations at predetermined intervals and of predetermined sizes, the radial depth of said interstices increasing from the conductor outwards, and gas in said interstices at a pressure below atmospheric and less than the critical. value for the largest radial dimension of any of said interstices.
  • Anelectriccablecomprilingaeonductonan n enclosing sheath and a dielectric material between the conductor and the sheath said material being constituted by turns and laminae of paper tape with spaces of definite and substantially invariable dimensions between the turns and of ⁇ increasing radial dimensions from the conductor outwards, said tape being fully impregnated with highly viscous compound which is conned to the paper under all working conditions, and gas occupying all said spaces, said gas being at a pressure substantially below atmospheric i and less than the critical value of the largest radial dimension for any of said spaces.
  • An electric cable comprising a conductor, an enclosing sheath and a dielectric material between the conductor and the sheath, said material being constituted by turns and laminae of paper tape with spaces of definite and substantially invariable dimensions between the turns and of increasing radial dimensions from the conductor outwards, said tape being fullyimpregnated with oil compound which has a setting point above the working temperature of the cable, and gas occupying all the said spaces, said gas being at a pressure substantially below atmospheric and less than the critical value for the largest radial dimensions of said spaces.
  • An electric cable comprising a conductor, an enclosing sheath and a dielectric layer between the conductor and the sheath, said layer comprising wrapped paper impregnated with highly viscous compound and gas at a pressure substantially below that of the atmosphere, which gas occupies spaces in the dielectric layer of dimensions predetermined in size so as to avoid ionization of gas and which spaces are substantially invariable in position and dimensions and are substantially clear of free compound under all working conditions, which spaces are distribuated through the dielectric layers.
  • An electric cable comprising a conductor, an enclosing sheath and a laminated dielectric layer between the conductor and the sheath, said layer comprising wrapped paper impregnated with highly viscous compound, and'gas, which gas occupies spaces ln the dielectric layer of substantially invariable dimensions which are bounded by the turns and laminae of the paper, which spaces are substantially clear of free compound under all working conditions, said gas being at a pressure substantially below that of the atmosphere and less than the critical value for the largest radial dimension of any of said spaces.
  • An electric cable comprising a conductor, and enclosing sheath and a laminated dielectric layer between the conductor and the sheath, said layer comprising paper impregnated with a compound which lhas a high setting temperature above the range of the working temperature of the cable and which compound is thereby retained in and confined to the paper under all working conditions, said layer also comprising gas, which gas occupies spaces of substantially invariable dimensions, which spaces are bounded by the turns and laminae of the paper, said gas being at a pressure substantially below that of the atmosphere and less than the critical value for the largest radial dimension of any of said spaces.
  • An electric cable comprising a conductor
  • said dielectric layer comprising wrapped paper impregnated with a highly viscous compound, said layer having helical spaces therein of mechanically predetermined locations and dimensions such that the dielectric strength ofv any radial dimension of said layer is predetermined,said spaces having gas therein at a pressure substantially below atmospheric and less than the critical value for the largest radial dimension of any of said spaces, the spaces being formed between edges of adjacent turns of paper and between surfaces of concentric wrappings.
  • An electric cable comprising a conductor, an enclosing sheath and a dielectric layer between the conductor and the sheath, said layer having helical spaces therein of mechanically predetermined locations and dimensions, said dielectric layer comprising wrapped paper impregnated with a highly viscous compound, the spaces being formed between edges of adjacent turns of paper and between surfaces of concentric wrappings, said spaces having gas therein at a pressure substantially below atmospheric and below the critical value for the largest radial dimension of said gas spaces, the dielectric strength of each part of said layer being predetermined by the dimensions of the spaces and the gas pressure.
  • An electric cable comprising a conductor, an enclosing sheath and dielectric material between the conductor and the sheath, said material being constituted by definitely spaced turns and layers of paper tape of predetermined thickness, which tape is fully impregnated with a highly viscous compound which is confined to the paper under all working conditions, all the spaces between the turns and layers of paper tape being occupied by gas at a pressure substantially below that of the atmosphere and below the critical value for the largest radial dimension of any of said spaces.
  • An electric cable comprising a conductor, an enclosing sheath and dielectric material between the conductor and the sheath, said material being constituted by denitely spaced turns and layers of paper tape of predetermined thickness, which tape is fully impregnated with oil compound which has a setting point higher than the working temperature of the cable, whereby the compound is conned to the paper under all working conditions, all the spaces between the turns and layers of paper tape being lled with gas at a pressure substantially below that of the atmosphere and below the critical value for the largest radial dimensions of any of the spaces.

Landscapes

  • Laminated Bodies (AREA)
  • Insulating Bodies (AREA)
  • Surface Heating Bodies (AREA)
  • Insulated Conductors (AREA)
US685192A 1932-09-27 1933-08-15 Electric cable Expired - Lifetime US2067170A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB26800/32A GB404412A (en) 1932-09-27 1932-09-27 Improvements in electric cables

Publications (1)

Publication Number Publication Date
US2067170A true US2067170A (en) 1937-01-12

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
US685192A Expired - Lifetime US2067170A (en) 1932-09-27 1933-08-15 Electric cable

Country Status (4)

Country Link
US (1) US2067170A (xx)
FR (1) FR760371A (xx)
GB (1) GB404412A (xx)
NL (1) NL36407C (xx)

Also Published As

Publication number Publication date
FR760371A (fr) 1934-02-21
GB404412A (en) 1934-01-18
NL36407C (xx)

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