Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B7/00—Insulated conductors or cables characterised by their form
  • H01B7/0009—Details relating to the conductive cores
  • H01B7/0036—Alkali metal conductors
• • 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
  • H01B9/0622—Cables for use in conduits under gas-pressure
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02G—INSTALLATION OF ELECTRIC CABLES OR LINES, OR OF COMBINED OPTICAL AND ELECTRIC CABLES OR LINES
  • H02G15/00—Cable fittings
  • H02G15/20—Cable fittings for cables filled with or surrounded by gas or oil
  • H02G15/24—Cable junctions

Definitions

• Electric power cables with extruded insulation over ccn- ductors in conduits are used for distribution cables, 5KV through 35KV, and for transmission cables, •69KV t_hrough 500KV.
• Moisture in the form of water vapor and air enters these cable • and conduit systems through the ends of conduit and by dif ⁇ fusion through the conduit walls.
• MDisture causes "water treeing" in extruded insulation in a few months, reducing the life of the insulation to approximately one fourth of an ex ⁇ pected 30 to 50 year life. Oxygen ages extruded insulation.
• Moisture barriers such as lead or alu ⁇ rinim sheaths, cemented metallic tapes, have been used over extruded insulation in newer installations to prolong their life, but add to the cost of the cable and do not exclude oxygen. Moisture and oxygen can corrode, or otherwise damage, aluminum and alummum- aluminu and aluminum-copper connections. At a higher cost, extruded insulation compounded with chemical additives has been developed to prolong insulation life in wet locations. Because sodium reacts violently in contact with water, sodium conductors are not practical in the presence of moisture. Should an arc occur in a cable, the presence of oxygen makes the damage due to burning or explosion much greater. Ihe problems caused by moisture and oxygen can be eliminated by evacuating the cable and conduit system to remove all moisture and air, then pressur ⁇ izing it with an inert gas.
• Ihpressurized extruded insulated cables in use during the recent 10 years were designed with extruded semiconducting materials under and over the insulaticn to exclude air at the surfaces of the insulation and to prevent ionization at operat ⁇ ing voltage.
• Insulaticn voids, ii ⁇ purities non-uniform conducting surf ces, curing ingredients, migration of materials in contact, and mixing ingredients have been a source of ioni- zati ⁇ n which shortens the life of the cable.
• a gas pressurized cable permits the use of bundles of aluminum redraw rods or sodium rods which have little, if any skin effect, and low alternating current resistance.
• the gas used would be SFg at a pressure of 20-80 psig.
• SFg a lower pressure can be used for the same voltage rating.
• the gas in a conduit ionizes it becomes a con ⁇ ductor which can act as a shield and a path for ground fault current which causes the circuit breaker to open the circuit which reduces damage to the conductors and does not damage the insulating properties of the gas.
• the life of conventional ("conventional" as used herein means - used before January 1, 1985) cable and conduit systems with extruded insulation and no vapor barrier that have been installed can be lengthened by fabricating the te_m ⁇ _nati ⁇ ns and pressurizing with gas at the site. Damage to conduits with pressurized gas can be reduced by adding an insect and rodent repellent as the gas that is dif ⁇ fused t_hrough the conduit wall helps keep them away.
• a leak of gas in the syste will cause a pressure drop along the line due to gas flow.
• the location of the leak can be determined.
• This invention relates to gas filled cable and conduit systems with extruded insulations on how to exclude moisture and air by evacuating, then pressurizing with a gas. This can be done at the installation site with cables and conduits that have been installed to increase their life or with new cables being installed. By excluding moisture and air, extruded in- sulaticn which is very economical in small sized conductors, can be used with a long life; and problems associated with low cost aluminum and even lower cost sodium conductors can be minimized.
• An extruded insulated cable and conduit system is described with an concentric neutral power cable with copper wires for the neutral and ground which is terminated and gas pressurized.
• An eccentric neutral bare aluminum conductor (laid parallel to the power cable) has a power,cable without semiconducting materials tinder and over the insulation.
• Aluminum ⁇ rods, cast or rolled into long lengths, are called redraw rods as they are drawn through dies to make small wires for stranded conductors. They are a lower cost conductor material than stranded wire.
• This invention describes how to make a low cost, large conductor, using multiple conductors of alu ⁇ num redraw rods or sodium rods for high voltage cables.
• the rods are laid par* allel in bunch stranding with each rod the same length.
• the in ⁇ dividual rod has no skin effect and the bunch has very little, if any, and the proximity effect is very low as the current density is low.
• FIG. 1 is cross-section of a gas pressurized, concentric neutral power cable in a conduit.
• Fig. 2 is a longitudinal section of a termination for the cable and conduit shown in Fig. 1.
• Fig. 3 is a cross-section of an eccentric neutral power cable in a conduit with gas pressure.
• Fig. 4 is a longitudinal section of a termination for the cable and conduit shown in Fig. 3.
• Fig. 5 is a cross-section of an eccentric neutral power cable using sodium conductors in conduit and with gas pressure.
• Fig. 6 is longitudinal section of a termination for the cable and conduit shown in Fig. 5.
• Fig. 7 is a cross-section of a cable and conduit using a shielded cable with a sodium conductor and crepe paper with gas pressure.
• Fig. 7A is a cross-section of a cable and conduit with multiple rods of sodium for a conductor inside a non-metallic pipe and similar to Fig. 7.
• Fig. 7B is a cross-section of a cable and conduit similar to Fig. 7A except the conductor is composed of three aluminum redraw rods inside a non-metallic pipe.
• Fig. 8 is a longitudinal section of a termination for the cable and conduit shown in Fig. 7.
• Fig. 1 showing a conventional cable, the numeral 1, indicates a central alt__inum conductor, with a conductor shield 2, made of an extruded semi-conducting material, surrounding it.
• Insulation 3 is extruded over conductor shield 2 and has an insulation shield 4, made of an extruded semi-conducting material over it. Multiple strands of solid wire, called con ⁇ centric neutral 5, are evenly spaced around and over, insulaticn shield 4.
• Non-metallic conduit 6 is pressurized with gas 7.
• a first end plate 8 has three holes; one, 9 slightly larger than conduit 6, a second, 10 slightly larger than stan 11 of tire valve 12, that has a seal 13 and a fast- ening nut 14, and a third, 15 slightly larger than first sleeve 16.
• the three holes should be arranged to make tire valve 12, and the terminal 17 accessible when installed and close together to make the outside diameter of first end plate 8 small and still permit the sealing of first end plate 8 to conduit 6.
• a second end plate 19 has a sleeve hole 20, slightly larger than second sleeve 21. Assemble tire valve 12 in hole 10 of first end plate 8 and seal sleeve 16, which may be a short piece of non- metallic conduit, in hole 15 by weld 22. Place first end plate
• Terminal 23 has a solid copper or aluminum barrel to fit seal 34 and hole in one end to fit conductor 1 which is fastened by crimp 24.
• the other end of the terminal 23 is adapted for connecting leads to, for example, by flat blade 25 and hole 26.
• Terminal 17 may be identical to terminal 23.
• conduits 6 and 32, end plates 8 and 19, and sleeves 16 and 21, would all be made of one plastic-like material which can be sealed to withstand continuous operating pressures of 80 psig and temperatures of 75 Centigrade.
• Sleeve 21, end plate 19 and enlarged conduit 32 could be molded in one piece, as could sleeve 16 and end plate 8, to reduce parts and in ⁇ stallation cost.
• Terminal 23 is brought out of the termination by inserting a seal, a rubber-like tube 34, into sleeve 21 and fastening with a band clamp 35.
• the length of sleeve 21 can be ex ⁇ tended several feet to reach a terminal block which is remote from the end of the conduit 6.
• the insulation 3 and conductor shield 2 would then be cut back or removed several feet and terminal 23 would be located remote from termination.
• the cable and conduit system is ready to evacuate and pressurized with gas.
• One method is to drill a hole 36 through the top of enlarged conduit 32, slightly smaller than the end of a one-half inch NPT pipe nipple, then screw in the nipple. Attach one end of hose to the nipple and the other end to a vacuum gage through a vacuum shut-off valve to a vacuum pump.
• Fig. 4 can be used. Conduit 6 is then pressurized to desired pressure by tire valve 12.
• the terminations shown in Figs. 2, 4, 6 and 8 can be used to splice cable and conduit systems. Two terminations joined is a splice.
• the cable, conduit and termination shown in Fig. 2 is used for a typical single phase circuit for high voltage residential underground distribution to feed padmount transformers.
• the construction would be similar except second end plate 19, would have three terminals 23, and seals and there would be three cables instead of one in conduit 6.
• the three cables may'have shielding tapes instead of wires which would be connected together and removed through sleeve 16 as a ground connection. If three concentric neutral cables were used for a three phase circuit, the three concentric wires would be jointed and removed through sleeve 16.
• the fabrication, evacua ⁇ tion, and gas pressurization of the terminations shown in Figs. 2, 4, 6, and 8 are similar. In Figs.
• an aluminum conductor 1, with extruded insulation 3 over it, has a bare aluminum neutral conductor 5, of equal size, laid in parallel to form a single phase eccentric neutral cable.
• the conductors would be solid aluminum for small conductor sizes and bundles of aluminum redraw rod for larger conductors.
• a cable can include a variety of numbers, sizes, and kinds of conductors in conduit 6 pressurized with gas 7.
• insulation 3 and a sodium eccentric neutral conductor 45 is used.
• a thin ⁇ ner extruded insulation 46 is used over 45. Because 46 is used primarily to mechanically strengthen 45, it can be made of a lower cost reclaimed meterial. Similarily, insulation 3 when pressurized with a gas can be a lower cost material.
• a terminal 47 has a conventional connection to a sodium conductor 44.
• a tapered, blade-like probe 48 is pushed into the sodium conductor 44 which is 'chesse-like' in structure with a cylindrical portion 49, of terminal 47, fitted closely over insulation 3.
• the neutral conductor 45 is brought out of the termination by connector 50, crimp 53, lead 52, crimp 28, and terminal 17, which is sealed by tube 30, sleeve 16 and clamp 31.
• Connector 50 is fastened to neutral conductor 45 and insulation 46, like terminal 23 is to conductor 44 and insulat ⁇ ion 3, respectively.
• FIG. 7 shows a single conductor high voltage cable with a large solid sodium conductor 55, that is covered by a thin, non- metallic, insulating pipe 56.
• a conductor shield 57 which is made of aluminum backed crepe paper tape or an aluminum tape and is used to reduce voltage stress.
• Over shield 57 is crepe paper tape insulaticn 58, and a thickness suitable for the voltage.
• Insulaticn shield 59 is similar to shield 57, covers insulation 58.
• Conduit 6 is pressurized with gas 7.
• Fig. 7A shows the same construction as shown in Fig. 7.
• the terminal for a large number of sodium rods, used as a single conductor, would have a corresponding nunfoer of probes 4 ⁇ .
• Fig. 7B shows a cable similar to that shown in Fig. 7A, except that in place of three sodium rods 60, three bare, aluminum redraw rods 61, are used. Miltiple aluminum redraw rods, used as a single conductor, would be crimped together in the terminal.
• Fig. 8 shows a termination for the cable shown in Fig. 7.
• the conductor shield 57 is connected to the con- ductor 55, at each end, by lapping shield 57 over terminal end 62 of terminal 63, then clamping shield 57 to 62 with stainless steel band clamp 64 which is non-magnetic.
• the insulation shield 59 is cut back one-half inch per 1000 volts, from the end of the insulation 58, then a stainless steel banding clamp 65 is used to clamp one end of a flexible lead 66 going around 59.
• the other end of lead 66 is attached to terminal 67 by crimp 28.
• Hand applied crepe paper tape insulation 69 and 70 covers clamps 64 and the end of insulation shield 59; respectively.
• Voltage stress on a conductor increases as the radius of that conductor decreases.
• a conductor shield 57 over pipe 56 and with conductor shield 57 connected to conductors 60 at each end, the voltage stress is greatly reduced, so the cable can operate at a higher voltage or less insulation thickness can be used.
• the conductors can move when the conduit is bent.
• New methods shown relate to using gas pressure to make and terminate various extruded insulated cables and crepe paper insulated cables of various types, sizes, and configerations for delivering high voltage electrical energy economically and with low losses. It is within the contemplated scope of this invention that numerous ' changes and variations can be made in the methods and materials without departing from the intended scope of the invention.
• Cable can be factory-built and terminated or field terminated.
• Conduit and cable can be factory or field assembled.

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• 1985
  • 1985-06-24 EP EP19850903731 patent/EP0227658A1/de not_active Withdrawn
  • 1985-06-24 WO PCT/US1985/001211 patent/WO1987000344A1/en unknown

Non-Patent Citations (1)

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