Underground Power Cable System For Lightning Strike Protection

Abstract

An underground power cable system including: an underground power cable, and a metallic mesh extending outside of and axially along the underground power cable.

Claims

1. An underground power cable system comprising: an underground power cable, and a metallic mesh arranged outside of and extending axially along the underground power cable.

2. The underground power cable system as claimed in claim 1, wherein the metallic mesh is spaced apart from the underground power cable.

3. The underground power cable system as claimed in claim 1, wherein the metallic mesh extends around a majority of the perimeter of the external surface of the underground power cable.

4. The underground power cable system as claimed in claim 1, wherein the metallic mesh extends around the entire perimeter of the external surface of the underground power cable.

5. The underground power cable system as claimed in claim 1, wherein the metallic mesh is made of galvanized steel or stainless steel.

6. The underground power cable system as claimed in claim 1, wherein the metallic mesh comprises metal wires that are welded together.

7. The underground power cable system as claimed in claim 1, wherein the metallic mesh has a mesh size of at least 1 cm.sup.2.

8. The underground power cable system as claimed in claim 1, wherein the metallic mesh is arranged on top of the underground power cable.

9. The underground power cable system as claimed in claim 1, wherein the metallic mesh is arranged laterally of the underground power cable along at least one side of the underground power cable.

10. The underground power cable system as claimed in claim 1, wherein the underground power cable comprises: a conductor, an insulation system arranged around the conductor, the insulation system including an inner semiconducting layer, an insulation layer surrounding the inner semiconducting layer, and an outer semiconducting layer surrounding the insulation layer, a metallic screen arranged around the insulation system, a water barrier layer arranged around the metallic screen, and an outer sheath defining the external surface.

11. The underground power cable system as claimed in claim 1, wherein the underground power cable is a DC power cable.

12. The underground power cable system as claimed in claim 1, wherein the underground power cable is a first underground power cable, and the underground power cable system includes a second underground power cable arranged generally parallel with the first underground power cable, wherein the metallic mesh extends outside of and axially along the second underground power cable.

13. A method of installing an underground power cable system, comprising: a) laying the underground power cable in a trench, and b) arranging a metallic mesh to extend outside of and axially along the underground power cable in the trench.

14. The method as claimed in claim 13, comprising placing backfill material over the underground power cable after step a), prior to step b), and placing further backfill material over the metallic mesh after step b).

15. The underground power cable system as claimed in claim 2, wherein the metallic mesh extends around a majority of the perimeter of the external surface of the underground power cable.

16. The underground power cable system as claimed in claim 2, wherein the metallic mesh extends around the entire perimeter of the external surface of the underground power cable.

17. The underground power cable system as claimed in claim 2, wherein the metallic mesh is made of galvanized steel or stainless steel.

18. The underground power cable system as claimed in claim 2, wherein the metallic mesh comprises metal wires that are welded together.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:

[0046] FIG. 1 shows a cross section of an example of an underground power cable;

[0047] FIG. 2 schematically shows a front view of a metallic mesh;

[0048] FIGS. 3A-3C show cross-sections of various examples of underground power cable systems installed in soil; and

[0049] FIG. 4 is a method of installing an underground power cable system.

DETAILED DESCRIPTION

[0050] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description.

[0051] FIG. 1 shows an example of an underground power cable 1. The exemplified underground power cable 1 may be a DC power cable or a single-phase AC power cable. Alternatively, the underground power cable could comprise more than one pole or phase.

[0052] The underground power cable 1 may be a medium voltage power cable, a high voltage power cable, an extra high voltage power cable, or an ultra-high voltage power cable.

[0053] The underground power cable 1 comprises a conductor 3.

[0054] The underground power cable 1 comprises an electrical insulation system.

[0055] The electrical insulation system comprises an inner semiconducting layer, or conductor screen, 5. The inner semiconducting layer 5 is arranged around the conductor 3.

[0056] The inner semiconducting layer 5 may for example comprise polymer mixed with conductive particles, or conductive paper.

[0057] The electrical insulation system comprises an insulation layer 7. The insulation layer 7 is arranged around the inner semiconducting layer 5. The insulation layer may comprise a polymer material, such as crosslinked polyethylene, polypropylene, EPR or EPDM rubber, or paper. The insulation layer 7 may be an extruded insulation layer or a wound insulation layer.

[0058] The electrical insulation system comprises an outer semiconducting layer 9, or insulation layer screen, 9. The outer semiconducting layer 9 is arranged around the insulation layer 7.

[0059] The outer semiconducting layer 9 may for example comprise polymer mixed with conductive particles, or conductive paper.

[0060] The underground power cable 1 comprises a metallic screen 11 arranged radially outside the outer semiconducting layer 9.

[0061] The metallic screen 11 may for example comprise a plurality of copper wires. The metallic screen 11 may be connected to electric ground.

[0062] The underground power cable 1 may comprise an inner water swellable tape arranged radially inside of the metallic screen 11 and an outer water swellable tape arranged radially outside of the metallic screen 11.

[0063] The underground power cable 1 may comprise a water barrier layer 13. The water barrier layer 13 is arranged around the metallic screen 11.

[0064] The water barrier layer 13 may for example have a laminated structure.

[0065] The water barrier layer 13 may comprise metal. The water barrier layer 13 may for example comprise aluminium, copper, or stainless steel.

[0066] The underground power cable 1 comprises an outer sheath 15. The outer sheath 15 may comprise one or more polymeric layers, for example at least one HDPE layer. The outer sheath 15 may be an extruded sheath.

[0067] The outer sheath 15 defines the external surface of the underground power cable 1. The outer sheath 15 has an outer surface, which is the external surface of the underground power cable 1.

[0068] FIG. 2 shows a front view of a portion of a metallic mesh 17. The metallic mesh 17 may for example comprise metal wires 19, 21 which have been welded together to form a mesh structure.

[0069] The metallic mesh 17 may for example comprise steel, such as galvanized steel or stainless steel. For example, the metal wires 19, 21 may be galvanized steel wires or stainless-steel wires.

[0070] The mesh size may for example be at least 1 cm.sup.2, such as at least 2 cm.sup.2, such as at least 3 cm.sup.2, at least 4 cm.sup.2, such as at least 5 cm.sup.2, at least 6 cm.sup.2, such as at least 7 cm.sup.2, at least 8 cm.sup.2, such as at least 9 cm.sup.2, at least 10 cm.sup.2.

[0071] FIG. 3A shows an example of an underground power cable system 23-1. The exemplified underground power cable system 23-1 comprises two underground power cables such as underground power cable 1, and the metallic mesh 17.

[0072] It is to be understood that the metallic mesh 17 may be used with a single underground power cable, or more than two underground power cables, instead of two underground power cables as shown in FIGS. 3A-3C.

[0073] The underground power cables 1 extend in parallel or generally in parallel with each other along their length. The underground power cables 1 are buried in the ground or soil 25.

[0074] The underground power cables 1 may be buried at the same burial depth in a flat formation. In examples comprising more than two underground power cables, the underground power cables may be arranged at the same burial depth in a flat formation or in a trefoil formation, for example. This holds for all examples presented herein.

[0075] The burial depth may for example be in the range of 0.5-2 m, such as 1-2 m.

[0076] In a cross-section along the longitudinal axes of the underground power cables 1, the metallic mesh 17 extends along a portion of the external surface of each of the underground power cables 1. The metallic mesh 17 is typically arranged within 1.5 m, such as within 1 m, such as within 0.5 m, from the underground power cables 1.

[0077] In the example in FIG. 3A, the metallic mesh 17 is arranged axially aligned with and vertically above the underground power cables 1. The metallic mesh 17 is arranged horizontally and extends laterally beyond each of the two underground power cables 1.

[0078] The metallic mesh 17 is arranged spaced apart from the underground power cables 1. The metallic mesh 17 could alternatively be in direct contact with the external surface of one or both of the underground power cables 1.

[0079] FIG. 3B shows an example of an underground power cable system 23-2 comprising two underground power cables such as underground power cable 1 and the metallic mesh 17. In this example, the metallic mesh 17 has been laid to extend along three sides of the underground power cables 1. The metallic mesh 17 is provided on top of the underground power cables 1, laterally of one of the underground power cables 1 and laterally of the other one of the underground power cables 1.

[0080] FIG. 3C shows an example of an underground power cable system 23-3 comprising two underground power cables such as underground power cable 1 and the metallic mesh 17. In this example, the metallic mesh 17 has been laid to extend along four sides of the underground power cables 1. The metallic mesh 17 thus encloses the underground power cables 1. The metallic mesh 17 is provided on top of the underground power cables 1, laterally of one of the underground power cables 1, laterally of the other one of the underground power cables 1, and vertically below the underground power cables 1.

[0081] A method of installing an underground power cable system, such as the underground power cable system 23-1, 23-2 or 23-3 will now be described with reference to FIG. 4.

[0082] The underground power cable system 23-1, 23-2 or 23-3 is installed in an excavated trench.

[0083] In a step a) the underground power cable 1 is laid in the trench.

[0084] In case of several underground power cables 1, each one is laid in the trench. In case the underground power cables 1 are laid in a flat formation, they are typically arranged spaced apart from each other.

[0085] In a step b) the metallic mesh 17 is arranged outside of and along the underground power cable(s) 1 in the trench.

[0086] The metallic mesh 17 may be arranged on one or more rolls that is/are unwound and arranged along the axial direction of the underground power cable(s) 1. According to one example, several rolls may be used to arrange metallic mesh 17 along different sides of the underground power cable(s) 1. For example, one roll may be used to arrange metallic mesh 17 laterally to one side of the underground power cable(s) 1 in the underground power cable system 23-2. Another roll may be used to arrange metallic mesh 17 laterally to another side of the underground power cable(s) 1. A third roll may be used to arrange metallic mesh 17 axially along the top of the underground power cable(s) 1.

[0087] Thus, the metallic mesh 17 arranged along the underground power cables 1 may at any point along the underground power cables 1 be formed of several metallic mesh subunits, each extending along a respective side of the underground power cables 1. Alternatively, the metallic mesh 17 may be formed of a single metallic mesh extending along the underground power cables 1.

[0088] In case the metallic mesh 17 is arranged to enclose the underground power cable(s) 1, the metallic mesh 17 is prior to step a) arranged underneath the underground power cable(s) 1. Backfill material/sand may be arranged over the metallic mesh 17 before the underground power cable(s) 1 are laid out in the trench.

[0089] Backfill material/sand may be placed over the underground power cable(s) 1 after step a), before step b). Further backfill material/sand may be placed on top of the metallic mesh 17 that has been placed on the lateral side(s) of the underground power cable(s) 1 and/or on top of the underground power cable(s) 1 to backfill the trench.

[0090] The inventive concept has mainly been described above with reference to a few examples. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.