Electric power transmission cables

Abstract

Electric power transmission cables containing a first portion provided with first armouring wires having a first tensile strength, the first armouring wires being made of a first metallic material coated with a first metallic protection coating with a thickness more than 100 g/m.sup.2, the first metallic material having a first magnetic permeability 1, a second portion provided with second armouring wires having a second tensile strength, the second armouring wires being made of a second metallic material coated with a second metallic protection coating with a thickness more than 100 g/m.sup.2, the second metallic material having a second magnetic permeability 2, and 21, the first armouring wires being longitudinally joined to the second armouring wires at a joint, the joint having a third tensile strength that is at least more than 80% of the lower tensile strength of the first tensile strength and the second tensile strength.

Claims

1. An electric power transmission cable, comprising: at least a first portion provided with a plurality of first armouring wires having a first tensile strength, said plurality of first armouring wires being made of a first metallic material coated with a first metallic protection coating with a thickness more than 100 g/m.sup.2, said first metallic material having a first magnetic permeability 1, at least a second portion provided with a plurality of second armouring wires having a second tensile strength, said plurality of second armouring wires being made of a second metallic material coated with a second metallic protection coating with a thickness more than 100 g/m.sup.2, said second metallic material having a second magnetic permeability 2, and 21, each of said plurality of first armouring wires being longitudinally and individually joined to one of said plurality of second armouring wires at a joint portion, said joint portion having a third tensile strength, wherein the third tensile strength is at least more than 80% of the lower tensile strength of the first tensile strength and the second tensile strength.

2. The electric power transmission cable according claim 1, wherein the electric power transmission cable is a tri-phase submarine electric power transmission cable.

3. The electric power transmission cable according to claim 1, wherein the first metallic material is carbon steel.

4. The electric power transmission cable according to claim 1, wherein the second metallic material is selected from austenitic steel, copper, bronze, brass, composite and alloys.

5. The electric power transmission cable according to claim 4, wherein the austenitic steel is austenitic stainless steel.

6. The electric power transmission cable according to claim 1, wherein at least one of said plurality of first armouring wires is longitudinally and individually joined to one of said plurality of second armouring wires by butt welded joint comprising resistive butt welding joint, flash butt welding joint and TIG welding joint.

7. The electric power transmission cable according to claim 1, wherein the diameter of said plurality of first armouring wire is the same as the diameter of said plurality of second armouring wire.

8. The electric power transmission cable according to claim 1, wherein the first and second metallic protection coatings are selected from zinc, aluminum, zinc alloy or aluminum alloy.

9. The electric power transmission cable according to claim 1, wherein the thickness of the first and second metallic protection coatings is in the range of 200 g/m.sup.2 to 600 g/m.sup.2.

10. The electric power transmission cable according to claim 1, wherein said first and second metallic protection coatings are hot dipped zinc and/or zinc alloy coating.

11. The electric power transmission cable according to claim 10, wherein said surface of the first metallic material and/or second metallic material are obtainable by a pre-treatment of electroplating with nickel, zinc and/or zinc alloy coating or being transferred under the protection of the tube filled with a heated reduction gas or gas mixture of argon, nitrogen and/or hydrogen to the galvanizing bath.

12. The electric power transmission cable according to claim 1, wherein the joint portion is painted with a compound comprising same elements as for the first or second metallic protection coatings.

13. The electric power transmission cable according claim 12, wherein the paint is extended from the joint portion along the first and the second armouring wires in a length less than 20 cm.

14. A composite wire, comprising: at least a first portion provided with a first wire having a first tensile strength, said first wire being made of a first metallic material coated with a first metallic protection coating with a thickness more than 100 g/m.sup.2, said first metallic material having a first magnetic permeability 1, at least a second portion provided with a second wire having a second tensile strength, said second wire being made of a second metallic material coated with a second metallic protection coating with a thickness more than 100 g/m.sup.2, said second metallic material having a second magnetic permeability 2, and 21, said first wire and said second wire being longitudinally and individually joined to each other at a joint portion, said joint portion having a third tensile strength, wherein the third tensile strength is at least more than 80% of the lower tensile strength of the first tensile strength and the second tensile strength.

15. A method for producing electric power transmission cables, comprising the steps of: (a) providing a first armouring wire having two ends and a first tensile strength, said first armouring wire being made of a first metallic material coated with a first metallic protection coating having a thickness more than 100 g/m.sup.2, said first metallic material having a first magnetic permeability 1, (b) providing a second armouring wire having two ends and a second tensile strength, said second armouring wire being made of a second metallic material coated with a second metallic protection coating having a thickness more than 100 g/m.sup.2, said second metallic material having a second magnetic permeability 2, and 21, (c) removing said first metallic protection coating away from one end of said first armouring wire to form a first end with said first metallic material, (d) removing said second metallic protection coating away from one end of said second armouring wire to form a second end with said second metallic material, (e) joining said first end and second end to form a composite armouring wire so that said first armouring wire and said second armouring wire are longitudinally and individually joined to each other at a joint portion, said joint portion having a third tensile strength, wherein the third tensile strength is at least more than 80% of the first tensile strength and the second tensile strength, (f) painting said joint portion, said first end and said second end with a compound comprising same elements as for said first or second metallic protect coatings, (g) cabling a plurality of said composite armouring wires to provide at least a first portion for an electric power transmission cable with plurality of said first armouring wires and at least a second portion for said electric power transmission cable with plurality of said second armouring wires.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

(1) The invention will be better understood with reference to the detailed description when considered in conjunction with the non-limiting examples and the accompanying drawings, in which:

(2) FIG. 1 shows a high voltage power cable according to prior art.

(3) FIG. 2 illustrates a cross-section of a tri-phase power cable having armouring wires.

(4) FIG. 3 illustrates a cross-section made along the longitudinal direction of the welded armouring wire according to the present invention.

MODE(S) FOR CARRYING OUT THE INVENTION

(5) FIG. 2 represents a cross-section of a tri-phase submarine power cable armoured with the steel wires of present invention. It includes a compact stranded, bare copper conductor 21, followed by a conductor shield 22. An insulation shield 23 is applied to ensure that the conductor do not contact with each other. The insulated conductors are cabled together with fillers 24 by a binder tape, followed by a lead-alloy sheath 25. The lead-alloy sheath 25 is often needed due to the severe environmental demands placed on submarine cables. The sheath 25 is usually covered by an outer layer 26 comprising a polyethylene (PE) or polyvinyl chloride (PVC) jacket. This construction is armoured by steel wire armouring layer 28. According to the invention, the steel wires 28 used may be welded steel wires with an adherent galvanized layer for strong corrosion protection. An outer sheath 29, such as made of PVC or cross-linked polyethylene (XLPE) or a combination of PVC and XLPE layers, is preferably applied outside the armouring layer 28.

(6) FIG. 3 is a cross-section made along the longitudinal direction of the welded armouring wire 30. In the example, the welded armouring wire 30 comprises two types of wires, low carbon wire 31, e.g. low carbon steel grade 65 according to EN10257-2, and stainless steel wire 33, e.g. stainless steel grade AISI 302. Both wires are coated with corrosion protection coating, e.g. zinc 32, 34.

(7) A steel wire, i.e. low carbon grade 65 or stainless grade AISI 302, e.g. having a diameter of 6 mm is first coated according to the following process.

(8) This steel wire is first degreased in a degreasing bath (containing phosphoric acid) at 30 C. to 80 C. for a few seconds. An ultrasonic generator is provided in the bath to assist the degreasing. Alternatively, the steel wire may be first degreased in an alkaline degreasing bath (containing NaOH) at 30 C. to 80 C. for a few seconds.

(9) This is followed by a pickling step, wherein the steel wire is dipped in a pickling bath (containing 100-500 g/l sulphuric acid) at 20 C. to 30 C. This is followed by another successive pickling carried out by dipping the steel wire in a pickling bath (containing 100-500 g/l sulphuric acid) at 20 C. to 30 C. for a short time to further remove the oxide on the surface of the steel wire. All pickling steps may be assisted by electric current to achieve sufficient activation.

(10) After this second pickling step, the steel wire is immediately immersed in an electrolysis bath (containing 10-100 g/l zinc sulphate) at 20 C. to 40 C. for tens to hundreds of seconds. The steel wire is further treated in a fluxing bath. The temperature of fluxing bath is maintained between 50 C. and 90 C., preferably at 70 C. Afterward, the excess of flux is removed. The steel wire is subsequently dipped in a galvanizing bath maintained at temperature of 400 C. to 500 C.

(11) Alternatively, after the second pickling process, the steel wire is rinsed in a flowing water rinsing bath. In this example, after the excess of water is removed, the wires are further transferred under the protection of the tube filled with a heated reduction gas or gas mixture of argon, nitrogen and/or hydrogen to the galvanizing bath. Preferably, the wires are heated to 400 C. to 900 C. in the tube before the galvanizing bath.

(12) A zinc coating is formed on the surface of the stainless steel wire by galvanizing process. After hot-dip galvanizing tie- or jet-wiping, charcoal or magnetic wiping can be used to control the coating thickness. For instance, the thickness of the galvanized coating is ranging from 100 g/m.sup.2 to 600 g/m.sup.2, e.g. 200, 300 or 400 g/m.sup.2. Then the wire is cooled down in air or preferably by the assistance of water. A continuous, uniform, void-free coating is formed.

(13) In order to form the welded wire of the present invention, the coating of both coated low carbon steel wires and coated stainless steel wires are stripped at one end portion of the wires, e.g. from 5 mm to 5 cm from the end. The exposed low carbon steel wire and stainless steel wire having the same diameter are welded, e.g. by flash butt welding or by resistive butt welding. The welded zone 36 in between the two wires as shown in FIG. 3 is intended to be kept thin, e.g. from 0.5 mm to 1 cm and preferably from 0.5 mm to 2 mm. The welded zone at the outside surface of the welded wire is grinded and subsequently painted with zinc based enamels 38 as shown in FIG. 3.

(14) Four types of wires are produced, tested and compared: type (I) low carbon steel wire standard grade 65, type (II) stainless steel wire standard grade AISI 302, type (III) welded wire and type (IV) welded wire which are both made by welding zinc coated type (I) wire and zinc coated type (II) wire. Type (III) welded wire is made by flash butt welding, while type (IV) welded wire is made by resistive butt welding.

(15) Before welding, the zinc coating at the intended welding zone of type (I) wire and type (II) wire is removed by mechanical stripping. This intended welding zone is further treated by hydrochloric acid pickling before welding to avoid intergranular corrosion which may occur due to the segregation of impurities, e.g. zinc during and after welding.

(16) The tensile strength or ultimate strength of the four types of wires is measured respectively. Tensile strength is the maximum stress that a material can withstand while being stretched or pulled before failing or breaking. The tensile strength is found by performing a tensile test. The two ends of a tested wire are griped respectively at two crossheads of the tensile test machine. The crossheads are adjusted for the length of the specimen and driven to apply tension to the test specimen. The diameter of the all four types of tested wires is the same, i.e. about 6 mm. For every test, the length of the wire between two crossheads is about 25 cm. The type (I) and type (II) wires are continuous wires, i.e. without welding or any connections means in-between. While for type (III) and type (IV) wires, the welded zone of two continuous parts are arranged approximately in the middle of two crossheads where the wire is fixed. The engineering stress versus strain is recorded during testing. The highest point of the stress-strain curve is the tensile strength. The applied maximum force, the tensile strength, yield strength, and the elongation at fracture of the four types of wires are summarized in table 1.

(17) As shown in table 1, average tensile strength of type (I) wire is about 814 MPa, and the average tensile strength of type (II) wire is about 672 MPa which is lower than type (I). The average tensile strength of type (III) wire is 577 MPa, and the average tensile strength of type (IV) wire is 646 MPa, both being more than 80% of type (II) wire, which is 67280%=537.6. It is also noted in the tensile testing that for type (III) wire, the broken point is at the welded zone. While for type (IV) wire, the broken point is located outside the welded zone and at type (II) wire section of the welded wire. These tests show the welded wires have a sufficient tensile strength to fulfill the requirement of armoring wires for power cables, in particular for type (IV) welded wire which performs even better than a continuous wire without welding.

(18) In addition, the yield strength (Rp.sub.P0.2) of the two types of welded wires is slightly higher than type (II) wire. The average elongation A (%) at fracture of type (III) and type (IV) wires is respectively 10% and 24%, which far exceeds 6% of the requirement for armouring wires.

(19) TABLE-US-00001 TABLE 1 The diameter of the wires in mm, the applied maximum force F(N), the tensile strength R.sub.m(MPa), the yield strength R.sub.P0.2(MPa), and the elongation A (%) at fracture of the four types of wires are listed. Dia. A No. Sample (mm) F(N) R.sub.m(MPa) R.sub.P0.2(MPa) (%) 1 I 6 23375 827 653 5 2 I 6 23147 819 661 6 3 I 6 22739 805 670 5 4 I 6 22789 806 638 5 5 I (Average) 6 23013 814 656 6 6 II 6 18451 674 343 43 7 II 6 18383 672 347 43 8 II 6 18301 669 341 43 9 II (Average) 6 18378 672 344 43 10 III 6 15961 586 365 11 11 III 6 15462 568 365 10 12 III (Average) 6 15711 577 365 10 13 IV 6 17507 646 370 23 14 IV 6 17592 649 389 24 15 IV 6 17453 644 366 26 16 IV 6 17505 646 374 22 17 IV (Average) 6 17514 646 375 24