DE2446755A1 - GAS-FILLED ELECTRIC POWER CABLE - Google Patents

Description

British Insulated Callender's Cables Limited, 21 Bloomsbury Street, London W.C.1., England

Priority is claimed for this application from British Patent Application No. 45937/73 dated October 2, 1973.

Gas-filled electrical power cable

The invention relates to gas-filled electrical power cables suitable for use in either alternating current or DC systems are suitable. GB-PS 393 694 describes gas-filled cables (sometimes and hereinafter as pre-impregnated Cables), in which the dielectric consists of wrapped paper tapes impregnated with a compound, which is only present in or on the surface of the paper, the gaps between the belts and any other spaces being filled with a generally pressurized inert gas are.

In practice, pre-impregnated gas-filled cables have consistently used nitrogen as the gas, albeit other gases Were considered. Sulfur hexafluoride appears to be the

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at first sight to be an attractive alternative for this gas, as it has a very high dielectric strength with only moderately increased Pressing as well as having good chemical stability. But as sulfur hexafluoride in one with pre-impregnated Paper insulated gas-filled cable was tried, it turned out to be completely unsatisfactory because the loss tangent increased unacceptably, followed by ionization created by it, that the cable was subjected to repeated pulses below the withstand voltage level.

It has now been found that this deterioration appeared only because of sulfur hexafluoride had been used with ordinary (cellulose) paper, and that these difficulties can be overcome by that the cable is made without the use of cellulose paper; and according to the invention comprises an electrical power cable Dielectric containing a multitude of tapes made entirely of one or more than one synthetic polymeric material having good dielectric properties, at least a portion of at least some of the tapes of felted fibers of this synthetic polymeric material (or at least one of these, if there are several) is formed, with also a compatible, non-drip insulating compound fills the pores between the felted fibers in the tapes, and taking insulating gas, which consists of sulfur hexafluoride alone or in admixture with one or more than one other stable insulating gas which is selected from the group is selected from nitrogen and the stable fluorinated and fluorochlorinated hydrocarbon gases, for example those sold under the trademarks "Arcton" and "Freon" are distributed, fills the spaces between these bands. The non-drip compound can also use the Cover the surfaces of the tape.

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The dielectric can be made entirely from felted fibrous tapes be formed, or, such bands can (preferably - alternatively) interspersed between tapes of the same or another suitable synthetic polymeric material in sheet form; Another possibility is to use a layered tape comprising a film, with a felted one fibrous layer is bonded to one or each side thereof. In some cases it may be desirable to have more than one to use these arrangements in separate parts of the dielectric, e.g. layered tape near the load bearing or to use the working current-carrying conductor of the cable where the electrical stresses are greater, and to use a simple fibrous tape in the other parts of the dielectric.

Suitable synthetic polymeric materials for use in either felted fiber form or in sheet form include the following: Polyethylene, polypropylene, polycarbonate, polysulphone, saturated linear polyester, polyphenyloxide, poly-4-methylpentene-1, Polytetrafluoroethylene, ethylene-propylene copolymers, fluorinated ethylene-propylene copolymers, perfluorostyrene, polyvinyl carbazole, Chlorotrifluoroethylene, polyvinyl indene fluoride ("Kynar") and ethylene-tetrafluoroethylene copolymer ("Tefzel"). Examples of felted synthetic polymeric fiber material include "Tyvec" polyethylene paper, "Nomex" polyamide paper (manufactured from EI Du Pont de Nemours & Co.), polypropylene fiber paper (manufactured by Minnesota Mining & Manufacturing Co.), as well glass wool bonded polyethylene.

Conventional non-drip compounds of the type as used in pre-impregnated gas-filled cables can be used, but connections at a relatively high level aromatic or unsaturated aliphatic hydrocarbon content are preferred because they tend to contain any Absorb gas which under discharge conditions

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is formed (this gas being hydrogen fluoride in the present case may include).

Examples of suitable compounds for use with any or each of the aforementioned polymeric materials are the following:

Connection A

low molecular weight polybutylene (Polyvis 00) 10-15% by weight

Polyethylene (WJG 11) 0-1 wt .- #

Polyisobutylene (Maxvis 2000) 0-5 ""

microcrystalline wax 0-4 ""

Vaseline up to 100 »»

Connection B

Hydrocarbon mineral oil (Sun ix) 40-50 wt .- ^

Coumarone Indene 50-40 ""

Vaseline (2 ILO) 30-5 ""

Polyisobutylene (Vistanex) 0-5 ""

(: 175cS viscosity at 90 ⁰ C dropping point 80-85 ⁰ C).

The gas pressure required will generally be less than for nitrogen, assuming the same Performance is required. Depending on temperature conditions, pressures can range from atmospheric pressure up to 1.7 MN / m (250 psi) can be used, but pressures sufficient to liquefy the sulfur hexafluoride should be avoided.

The invention will now be described with reference to the drawing, which shows it by way of example

Pig. 1 shows a schematic section of an inventive

Cables,
Pig. 2 shows a schematic cross section through this cable,

while
Pig. y shows an enlarged schematic cross-section of a small portion of the cable dielectric.

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24A6755

The cable shown has three metallic conductors 1 carrying the working current, around which conductive (carbon-laden) Plastic strips 2 are applied, which form conductor shields. On each conductor shield are the dielectric 3, which will be described in detail below, and a dielectric shield 4 applied, which also is formed from conductive plastic tapes. The spaces between the cores or veins are filled with fillers filled in, the open, helical gas ducts 15 record; and a pressure-tight cover layer, which for example consists of a metal jacket 6 and a protective cover exists, is upset.

Like from Pig. 3 shows the cable dielectric is off pre-impregnated tapes 8, each of which consists of a plastic film layer 9 sandwiched between two layers 10 is sandwiched from synthetic plastic paper and bound to this. The synthetic paper layers are completely pre-impregnated with a non-drip compound which also has a very thin coating 11 on the main surfaces of the Band and possibly also at the edges. The tapes are wound around with a small "butt joint" gap between the tape edges running helically To form gas spaces 12 which are filled with compressed sulfur hexafluoride. The materials used in this volume can be selected from the substances mentioned above, a preferred combination of polypropylene film, polypropylene paper and the material identified above as "Compound B".

In addition to the advantage of achieving the required alternating current and impulse stability at a much lower Pressure, the use of sulfur hexafluoride has the advantage of an improved cooling effect when the gas is through a pipe is circulated, which is located in the cable ladder, or

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through a pipe in which one or more than one cable core is installed and then through suitable heat exchanger devices, which are arranged, for example, at the connection points, together with a slight reduction in thermal resistance the insulation.

Claims

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Claims (7)

- 7 74 044
Kü / Schm 30 Sept. 1974 Claims Electric power cable with a dielectric comprising a plurality of ribbons, at least a portion of at least some of the tapes is formed from felted fibers with a compatible, non-drip insulating Compound fills the pores between the felted fibers in the tapes and with an insulating gas in the gaps fills between the bands, characterized in that the bands are made entirely of one or more than one synthetic polymer Material with good dielectric properties are composed and that the gas consists of sulfur hexafluoride alone consists of or is mixed together with one or more than one other insulating gas selected from the group, those made of nitrogen and the stable fluorinated and fluorochlorinated Hydrocarbon gases. 2. Cable according to claim 1, characterized in that between the felted fibrous ribbons, ribbons made of synthetic polymeric material are interspersed in the form of a film. 3. Cable according to claim 2, characterized in that the fibrous strips and the foil strips alternate with one another. 4. Cable according to claim 1, characterized in that the tapes consist of a film, a felted fibrous Layer is bonded to one or each side thereof. 5. Cable according to claim 1, characterized in that part of the dielectric in the vicinity of the working current leading The conductor of the cable is formed from layered tapes, each having a foil, with a felted fibrous layer bonded to one or both sides thereof and wherein the outer portion of the dielectric is formed from simple fibrous tape is. 509815/0959 6. Cable according to one or more of claims 1 to 5, characterized in that the insulating compound is 10-15 wt. # low molecular weight polybutylene, 0-1 wt. # polyethylene, 0-5 wt. # Polyisobutylene, 0-4 wt. $ Microcrystalline wax with the remainder consisting of petroleum jelly. 7. Cable according to one or more of claims 1 to 6, characterized in that the insulating connection 40-50 Weight # hydrocarbon mineral oil, 30-40 weight, # coumarone indene, 30-5% by weight of petroleum jelly and 0-5% by weight of polyisobutylene. 509815/0959