Patent ID: 12253730

FIGS.1and2show a prior art system100for guiding a dielectric cable4from conductor2to an tower6,6a.The conductor2can also be generally identified as a power transmission cable, and the tower6,6aas any elevated support structure as discussed above. The conductor2may be a high-voltage cable. High-voltage may generally be defined as a voltage greater than 650V AC. Particularly, high-voltage may be defined as a voltage above 1000V AC.

As can be seen in these Figures, the dielectric cable4is preferably wrapped around the conductor2in a helical path. However, the dielectric cable4may be installed along the conductor2in any suitable manner. For example, the dielectric cable4may be installed along the conductor2by lashing. In this sense, the dielectric cable4is supported by the conductor2. InFIG.1, the conductor2reaches the tower6and is electrically isolated therefrom via an insulator7. The conductor2is electrically connected to the next conductor in an adjacent span (not shown) via a jumper lead9. InFIG.2, the lattice tower6ais a suspension tower; it only holds up the conductor2via the insulator7. As stated above, the tower6,6amay be any conventional support structure known in the art, including but not limited to poles (wooden or concrete)6, lattice towers6aor any other suitable structure.

As discussed above, the conductor2is at a high voltage (typically 33 kilovolts) and it is therefore necessary to have a safe way to bring the dielectric cable4down to a ground potential. Conventionally, this has been achieved by means of an insulator12with a bore extending along its length. In particular, the insulator12may be in the form of a tube. This insulator12has a surface made of anti-tracking (or track-resistant) material. The upper section of the insulator12is provided with sheds14to increase the phase-to-ground surface resistance and thereby limit potentially damaging surface leakage currents. A corona ring16may also be provided to supress corona discharge from any metalwork.

The dielectric cable4is fed down the bore of the insulator12and the annulus between the dielectric cable4and the bore is filled with a liquid insulating material that sets over a given period to a gel. This solid construction is waterblocked and therefore prevents the flow of potentially damaging internal leakage currents. The insulator12is generally flexible and may be secured to the tower6via an attachment bracket13. This attachment bracket13is connected to an earth point15and acts as a lower (earthed) end of the insulator12. The dielectric cable4can then extend from this lower section of the insulator12(i.e. below the bracket13) as shown inFIG.1to ground level for use as necessary. In particular, the dielectric cable4may extend via a downpipe18to connect to the next component, for example an underground cable (not shown). The downpipe18may be made of a relatively cheap material as it does not have any special insulating properties as it is provided downstream of the bracket13which acts as the grounding point for the insulator12. In this case the section of insulator12between the earthing point13and the downpipe18also does not need to have any special insulating properties.

This prior art system100requires the use of an insulator12to guide the dielectric cable from the conductor2to the support structure6. The entire length of this insulator12may be subject to the phase-to-ground voltage and therefore the entire length must be made to withstand potentially damaging surface leakage currents. This in part is achieved by ensuring that the surface is made of anti-tracking components. Since these components are relatively expensive this is not a cost effective solution, particularly in the case where an earthing bracket13is used.

In a typical installation, splices are needed at intermediate locations. In some situations, access to the splices may be required without de-energising the overhead power line. Accordingly, two of the systems100shown inFIG.1andFIG.2are provided back-to-back so a splice enclosure can be mounted between them at ground potential and hence can be accessible from the ground without the need to de-energise the powerline.

A system200for guiding a dielectric cable4from a conductor2to a support structure6csuch as a tower according to the present invention is shown inFIGS.3and4.FIG.3shows the system200being used as an in-line splice, with the dielectric cable4continuing to be supported by the conductor2beyond the insulator22. The in-line splice arrangement will be described in detail below. In summary, a first section of the dielectric cable4extends from the conductor2, and a second section of the dielectric cable4extends back up to the conductor2.

FIG.4shows the system200, with only the first section of the dielectric cable4shown. Thus, the system200shown inFIG.4is not operating as an in-line splice. The technical functioning of the system200ofFIGS.3and4are substantially the same and will be described collectively below.

This system200is generally similar to the prior art system100described above. The dielectric cable4is likewise wrapped or in any case attached to the conductor2, and is guided from this conductor2to the support structure6c.

An insulator22is provided attachable to the conductor2. The insulator22is preferably freely hanging from the conductor2. That is, the lower end of the insulator22is not directly attached to the tower. The insulator22may be, for example, rated at 35 kilovolts for use with a powerline voltage of 33 kilovolts. In embodiments discussed in more detail below, the insulator22may be formed of one or more insulator sections attached to one another. The insulator22is relatively large in diameter. In particular, the diameter of the insulator22may be greater than 90 mm, greater than 100 millimetres, or greater than 110 millimetres. Particular embodiments may have diameters of approximately 95 millimetres, 110 millimetres, or 120 millimetres. At least one bore56passes through the insulator22and the dielectric cable4extends through this bore56. The bore56may be filled with a gel in the usual manner as described above in relation to the prior art system100. Unlike the prior art system100, the insulator22does not span from the power conductor2to the tower6c.The lower end of the insulator22is generally freely hanging from the power conductor2.

Typically, the minimum length of the insulator22may be 300 mm for a typical 33 kV overhead powerline. The insulator22may of course be longer as this would increase its rated voltage. In particular embodiments, the insulator22may have a total length of less than 600 mm, preferably a total length of less than 500 mm, more preferably a total length of less than 400 mm. In specific embodiments, the insulator22may have a total length of approximately 300 mm. An earth bond23extends from the earth potential15up to the lower end of the insulator22as can be seen inFIGS.3and4. The earth bond23is electrically connected to earth potential15. This earth bond23may typically be a small diameter metal wire which is attached to the base of the insulator22and the earth. The earth bond23may be carried within a downpipe28. The downpipe28also receives the dielectric cable4and act to physically support the dielectric cable4between the lower end of the insulator22and the tower6.

As the insulator22is connected to the earth bond at its lower end, the entire length of the downpipe28does not need to have any particular electrical properties. Accordingly, it can be a simple plastic component which can be readily fitted to length as required. The downpipe28spans a gap between the insulator22and the tower. This contrasts the prior art where the insulator extends all the way to the tower.

This minimises the length of phase-to-ground insulator required.

An isolated view of an insulator section22A is shown inFIG.5. The insulator section22A may be formed of first and second end portions54A,54B and a central section52extending there between. The first and second end portions54A,54B comprise first and second end flanges which extend radially outward of the central section52. The central section52may be formed of an insulating material, for example an epoxy resin. The central section52may further comprise a plurality of sheds (or radial projections) as shown inFIG.5.

Each end portion54A,54B may be a conductive material such as metal end plates. The metal end plates may be, for example, cast into in the ends of the insulator section22A.

Given the relatively large diameter of the insulator section22A, the two through bores56may be formed there through. However, in alternative embodiments only a single bore56may be formed through the insulator section22A. The two through bores56may be separated by a distance greater than 40 millimetres, preferably greater than 55 millimetres, more preferably greater than 65 millimetres. In particular embodiments, the distance between the two through bores56may be approximately 45 millimetres, 60 millimetres or 70 millimetres. This allows one or two dielectric cables4to pass through the insulator section22A. In particular, this may allow a splice location to be located with a single system200according to the present invention.

That is, the dielectric cable4may extend from the power transmission cable2into a first of the bores56down towards a splice location and then up via the other of the bores56to then re-join the power transmission cable2. This is a much simpler system than the prior art which requires two systems100in order to include an intermediate splice location. Each dielectric cable may pass through the same downpipe28. Alternatively, first and second downpipes may be provided with each dielectric cable passing through its own downpipe28. This provides an in-line splice as shown inFIG.3. Of course, it is possible to route only a single section of the dielectric cable4through the insulator22, such as in the system200ofFIG.4.

As mentioned above, the insulator22may be formed of one or more insulator sections22A. Each insulator section22A may be rated to a particular voltage, for example between 33 and 40 kilovolts, preferably 35 kilovolts. Alternatively, each insulator section22A may be rated to a lower voltage, for example between 11 and 20 kV. A single insulator section22A may be used as an insulator22if the single section22A is rated for a sufficiently large voltage. For example, if a single insulator section22A is rated to 35 kilovolts it may be used with a transmission line at 33 kilovolts. In this sense, the above description may apply in its entirety to an insulator22as a whole formed of a single insulator sections22A.

In cases where it is necessary to be rated to a higher voltage (for example 70 kilovolts) multiple insulator sections22A may be connected together to form a single insulator22. In order to achieve this the top and bottom ends54A,54B of the insulator sections22A may comprise attachment regions58A,58B. In particular, one end of the first and second ends54A,54B may comprise a threaded tapped hole58B as shown inFIG.5A. This threaded tapped hole58B may be blind tapped hole as shown in this Figure or may extend through the flange of the central portion52.

The top of the top insulator section22A and the bottom of the bottom insulator section22A may follow the design of the single section insulator22to enable the multiple section insulator to be installed in a similar manner. In particular, the downpipe28and earth bond23are used to provide the necessary adaptability while keeping the cost to a minimum.

At the upper end of the insulator section22A there is a provided a clearance hole58A extending through the end54A and a flange of central portion52. This clearance hole58A may be a recessed as shown in the Figures with an internal shoulder so that the screw heads do not sit proud of the insulator surface. This clearance hole58A receives a screw or other fastening component for attaching to a corresponding attachment means58B of a further insulator section. This allows each insulator section to act as a complete insulator in its own right or be attached to another in order to form an insulator rated for a high voltage. This ensures easy scaling of the system as appropriate.

The system200is installed by attaching the insulator22to the conductor2. The dielectric cable4is passed through the insulator22via a bore formed therein. A length of downpipe sufficient to bridge the distance between the lower end of the insulator22and the tower6,6amay then be cut. This can be done in advance of the installation or may be done in the field based upon measurements taken as the system200is being installed. The dielectric cable4is then passed through this downpipe28. An earth bond23is then connected to a lower end of the insulator22and is attached to or received in the downpipe28. At some convenient point (e.g. via metallic coupling30) the electrical connection to the earth15is made. In this embodiment the bracket13performs no electrical (i.e. earthing) function and its use may be optional if the downpipe28does not need support. The downpipe28is then attached to the tower6cand continues with the cable4all of the way down the tower6c.In this manner, the system200according to the present invention can be readily tailored for the particular location.