AU2001290383B2 - Electrical cabling system for high voltage networks - Google Patents

Description

WO 02/27734 PCT/NZOI/00195 ELECTRICAL CABLING SYSTEM FOR HIGH VOLTAGE NETWORKS Field of Invention This invention relates to an electrical cable system that can be readily used for the transmission of power over a high voltage network.

Description of Background Information Known high voltage cabling systems may be classified into two categories. The first category includes modern cables constructed of a copper or aluminium conductor(s) covered with layers of extruded cross linked polyethylene (XLPE), laid up together, and sheathed in XLPE and/or poly vinyl chloride (PVC). These cables are now extensively used for standard high voltage arrangements up to and including 11 OkVac (kV 1000V) (prior art drawing Figure 1).

The second category includes older cables constructed of aluminium or copper conductors insulated with bound wood pulp paper tape. The conductors are laid up together and the paper tape insulation impregnated with an oil and wax mixture to promote insulation. The complete assembly is sheathed in lead to resist the ingress of moisture (prior art drawing Figure These cables, being older in design and manufacture, still exist in many installations, but by and large are being replaced with the new technology XLPE type cables (Figure 1).

All cables generate heat, which is usually radiated or extracted through forced or natural air circulation. In the case of specific conductor arrangements, particularly those used in generators, the cooling is by hydrogen gas circulation. The techniques required for hydrogen cooling are well known and have been in commercial operation for many years.

WO 02/27734 PCT/NZOI/00195 2 Both cable types (Figures 1 and 2) are manufactured in a continuous process that takes the raw copper or aluminium conductor and extrudes or binds on the insulation layers. Separate processes are used to lay individual conductors into a cable structure and extrude the outer sheathings. Due to these processes and the mechanical handling difficulties in their construction the conductor size, and hence its current carrying capacity has practical limits. Multiple parallel conductors are often used to transmit the necessary current at a desired transmission voltage.

The cables produced by these techniques are in long lengths so providing difficulty in installation where the cable cannot be directly laid but must be drawn through an aperture, a common installation condition.

An object of the invention is therefore to provide a cabling system that is easy to manufacture, can be easily handled, and has a greater current carrying capacity than the present cabling systems.

A further object of the invention is to provide an electrical cabling system having the capability of conducting higher currents than is commonly available while providing ease of installation and construction.

SUMMARY OF INVENTION According to a first aspect of the invention there is provided a cable conductor including one or more extruded aluminium tube(s) tapped with two layers of aqua dagged semi-conducting tape wrapped with a 50% displacement.

Each tube can be 20 metres in length and the ends of each tube are left unwrapped for site terminations and jointing.

According to a second aspect of the invention there is provided a method of installing the wrapped tube(s) cable conductor according to the first aspect into a mould into WO 02/27734 PCT/NZOI/00195 3 which an insulating resin is entered under vacuum before the completed assembly is cured to form a conductor assembly.

According to a third aspect of the invention there is provided a method for installing the completed conductor assembly from the second aspect within selected PVC tubes so that the complete resin conductor is supported within the center of the PVC tube.

According to a fourth aspect of the invention there is provided a method of joining the ends of successive completed conductor assemblies and effecting a site resin filled joint at the join so made.

According to a fifth aspect of the invention there is provided a method of joining the outer PVC tube layers using a sleeve secured by pumped adhesive.

According to a sixth aspect of the invention there is provided an electrical cabling system for high voltage networks that can be used in place of conventional high voltage cabling systems, said electrical cabling system including: one or more extruded aluminium tube conductors, a twin layer spiral wound semi-conducting layer on each aluminium tube conductor, a cast resin insulated layer applied under vacuum in a mould to each conductor tube to form a conductor assembly, an inner insulated centralising support structure, an outer PVC tube covering, a void between the conductor assembly and PVC outer tube for cooling, the dimensions of the said components determining the current carrying capability at any one applied voltage.

WO 02/27734 PCT/NZOI/00195 4 The void between the conductor assembly and the PVC outer tube may be cooled by hydrogen gas or another suitable coolant.

Further aspects of the invention which should be considered in all its novel aspects will become apparent from the following descriptions which are given by way of example.

BRIEF DESCRIPTION OF DRAWINGS The above, and other objects, features and advantages of the present invention will be made apparent from the following descriptions of the preferred embodiments, given as non limiting examples, with reference to the accompanying drawings.

Figure 1 is a cross section of a prior art XLPE insulated cable system viewing of which is simplified by removal of its semi-conducting layers.

Figure 2 is a cross section of a prior art paper insulated cable system simplified by the removal of its semi-conducting layers.

Figure 3a is a longitudinal cross section of a resin tube conductor assembly for a single conductor.

Figure 3b is a detail on an enlarged scale of the region X of the resin tube conductor assembly shown in Figure 3a.

Figure 3c is a perspective view of an end of the conductor assembly shown in Figures 3a and 3b.

Figure 3d is an end view of the conductor assembly shown in Figures 3a to 3c.

WO 02/27734 PCT/NZOI/00195 Figure 4a is a longitudinal cross section of a straight length of an electrical cable system according to the invention comprising the resin tube assembly with a PVC tube and centralising support structures and showing a site join between two similar assemblies.

Figure 4b is a perspective view of the length of electrical cable system shown in Figure 4a with part of the outer PVC sheath removed at the join for clarity.

Figures 5a and 5b are diagrams of specialised tees, and radius bends using the electrical cable system.

Figure 6 is a table of the current carrying values of the electrical cable system depending on the thickness of insulation and tube diameter and wall thickness.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figures 3a to 3d show an insulated conductor assembly according to a first embodiment of the present invention. The conductor assembly is manufactured by: preparing an extruded aluminium tube 1 to accept a semi-conduction layer 2 that is applied as an aqua dagged tape, spiral wound with a 50% overlay between the top and bottom layer. The completed tube is entered and supported within a mould and impregnated under vacuum with a resin 3 to form a heat conduction and electrical insulation layer around the conducting aluminium tube 1. The thickness of the resin is adjusted according to the required normal operating voltage (1 9mm for voltages up to and including 11 OkVac and 35mm for voltages greater than 110kV and less than or equal to 250kVac). The resin can be a mix of an electrical casting resin, quartz flour, diatematus earth and wool. As is shown the end of the tube 1 is left unwrapped for site termination and jointing.

WO 02/27734 PCT/NZOI/00195 6 Figures 4a and 4b show a completed conductor length according to a second embodiment of the present invention. A single conductor is manufactured by: supporting a resin encased conductor assembly 4 at regular intervals by insulated centralising supports 5 that maintain the conductor assembly within the center of a PVC outer tube 6. The supports 5 are arranged to allow free flow of a cooling media such as hydrogen gas around the conductor bundle 4.

The ends of the aluminium tube 1 in the conductor length are exposed (Figure 4b) for site jointing and final installation.

In Figures 4a and 4b the site joint is manufactured by site welding at Y of the aluminium tube 1 using certified welding techniques to specified British Standards (BS) or ASME Codes of practice. The tubes are bound with semiconductor tape 2, which secures the joint area and a detachable site joint mould 7 is placed in position.

The join is then impregnated with resin 3 through inlet 9. The resin impregnation may be under vacuum via a vacuum plug 10. A PVC outer piping sleeve 8 is placed over the resin joint after curing. The PVC sleeve 8 is fixed by adhesive in position.

Figures 5a and 5b show completed conductor tee and sweeping bend cable system arrangements. These are manufactured using formed conductor assemblies 4 and deformed PVC pipe 6.

Figure 6 shows a table of the current carrying capacity of the invention in relationship to the diameter and wall thickness of the aluminium tubing 1 used and the thickness of the resin insulation 3 used.

The electrical cable system, when installed, would be cooled by a coolant such as hydrogen gas placed within the space between the outer PVC tube 6 and the cable assembly 4.

WO 02/27734 PCT/NZO1/00195 It should be noted that the dimensions and ratings of the cables and their portions and components mentioned above are cited merely as examples and should not be construed as limiting.

Although the invention has been described with reference to particular means, materials, and embodiments, it is to be understood that the invention is not limited to the particulars disclosed and extends to all equivalents within the scope of the claims.

Claims (8)

1. A cable conductor including one or more extruded aluminium tube(s) tapped with two layers of aqua dagged semi-conducting tape wrapped with a displacement.

2. A cable conductor as claimed in claim 1 wherein each tube is about 20 metres in length and the ends of each tube are left unwrapped for site terminations and jointing.

3. A cable conductor as claimed in claim 1 or claim 2 wherein the wrapped tube(s) cable conductor is placed into a mould into which an insulating resin is entered under vacuum before the completed assembly is cured to form a conductor assembly.

4. A cable conductor as claimed in claim 3 wherein the insulating resin is a mix of an electrical casting resin, quartz flour, diatematus earth and wool, A cable conductor as claimed in claim 3 or claim 4 wherein the completed conductor assembly is placed within selected PVC tubes so that the complete resin conductor is supported within the center of the PVC tube.

6. A cable conductor as claimed in claim 5 wherein the ends of successive completed conductor assemblies are joined on a site with resin at the join so

7. A cable conductor as claimed in claim 6 wherein the outer PVC tube layers are joined using a sleeve secured by pumped adhesive.

8. An electrical cabling system for high voltage networks that can be used in place of conventional high voltage cabling systems, said electrical cabling system including: one or more extruded aluminium tube conductors, a twin layer spiral wound aqua dagged semi-conducting layer, wrapped with about a 50% displacement on each aluminium tube conductor, AiVENDED SHEET IPEA/AU ,L PCT/NZ01/00195 Received 22 August 2002 9 a cast resin insulated layer applied under vacuum in a mould to each conductor tube to form a conductor assembly, an inner insulated centralising support structure, an outer PVC tube covering, a void between the conductor assembly and PVC outer tube for cooling, the dimensions of the said components determining the current carrying capability at any one applied voltage.

9. An electrical cabling system as claim in claim 8 wherein the void between the conductor assembly and the PVC outer tube is cooled by hydrogen gas or another suitable coolant. A cable conductor as described in claim 1 or claim 8 wherein specialised bends and tee joints are manufactured. ASPEC87349 AMlEV' lED SHEET IF ENAU