HVAC-cable with composite conductor

Abstract

A high voltage alternative current cable is provided having mechanically reinforced electric conductor, by having a reinforcement member at the centre of the conductors of the cable, where the reinforcement member is made of one or more low or non-magnetic steel wires, one or more wires of CuNiSi precipitation alloy, or one or more aluminium wires made of an EN AW-1xxx, EN AW-2xxx, EN AW-5xxx, AW-6xxx, EN AW-7xxx, or EN AW-8xxx alloy, according to the European aluminium standard.

Claims

1. A power cable comprising: at least one conductor having a longitudinal centre axis and an outer sheathing encompassing the at least one conductor, wherein each of the at least one conductor comprises: a current conducting material, and an electric insulating material enclosing the current conducting material, and wherein the at least one conductor further comprises a reinforcement member located at the longitudinal centre axis of the conductor and where reinforcement member is embedded in and enclosed by the current conducting material, and where the reinforcement member is made of either: one or more steel wires, one or more wires of CuNiSi precipitation alloy, or one or more aluminium wires made of an EN AW-1xxx, EN AW-2xxx, EN AW-5xxx, AW-6xxx, EN AW-7xxx, or EN AW-8xxx alloy, according to the European aluminium standard.

2. The power cable according to claim 1, wherein the power cable comprises three conductors.

3. The power cable according to claim 1, wherein the reinforcement member is made of a low or non-magnetic steel.

4. The power cable according to claim 3, wherein the low or non-magnetic steel is chosen from one of; an austenitic steel or a duplex steel, preferably one of AL 4565 superaustenitic stainless steel (UNS 34565), AISI 304 Stainless Steel (UNS S30400), AISI 316 Stainless Steel (UNS S31600), duplex steel UNS S31803 (EN 1.4462), super-duplex steel UNS S32750 (EN 1.4410), or lean duplex steel UNS S32304 (EN 1.4362).

5. The power cable according to claim 1, wherein the reinforcement member is either a single monolithic wire or is composed of a plurality of twined or not twined wires arranged in a bunt.

6. The power cable according to claim 1, wherein the current conducting material is a metal or metal alloy having an electric conductivity of at least 2.9.Math.10.sup.7 S/m at 20° C., preferably of at least 5.0.Math.10.sup.7 S/m at 20° C. and most preferably of at least 6.Math.10.sup.7 S/m at 20° C.

7. The power cable according to claim 6, wherein the current conducting material is one of: Cu, Cu-alloy, Al, or an Al-alloy.

8. The power cable according to claim 6, wherein the current conducting material is a monolithic shell/layer laid radially around the reinforcement member or is made of a plurality of wires of the current conducting material surrounding the reinforcement member.

9. The power cable according to claim 1, where the electric insulation material is made of one of; ethylene propylene rubber (EPR), ethylene propylene diene monomer (EDPM), rubber, polyethylene (EP), polypropylene (PP), polyurethane (PUR), cross-linked polyethylene (XLPE), or mass-impregnated (MI) paper.

10. The power cable according to claim 1, where the power cable further comprises a semiconducting conductor screen arranged radially around the current conducting material, and where the semiconducting conductor screen is made of a polyethylene-based material constituted of either low density polyethylene (LDPE), a linear low density polyethylene (LLDPE), a medium density polyethylene (MDPE), or a high density polyethylene (HDPE), or a copolymer of ethylene with one or more polar monomers of; acrylic acid, methacrylic acid, glycidyl methacrylate, maleic acid, or maleic anhydride made semiconducting by addition and homogenisation of until 40 weight % particulate carbon in the polymer mass.

11. The power cable according to claim 1, where the power cable further comprises an inner sheathing laid either as an outermost layer of each conductor of the cable or laid around a cable core, and wherein the inner sheathing is made of either a metal foil/layer of: a) Al or an Al-alloy of an AA1xxx series, an AA5xxx series or an AA6xxx series alloy according to the Aluminium Association Standard, b) Cu or a Cu-alloy, a CuNi-alloy, or a CuNiSi-alloy, c) Fe or a Fe-alloy, a SS316 alloy or a S32750 alloy according to the ASTM A240/A240M-20a standard, or d) Pb or a Pb-alloy, or a laminate of a metal foil/layer of: one of a), b), c) or d) and a polyethylene-based polymer chosen from one of; a low density polyethylene (LDPE), a linear low density polyethylene (LLDPE), a medium density polyethylene (MDPE), or a high density polyethylene (HDPE), or a copolymer of ethylene with one or more polar monomers of; acrylic acid, methacrylic acid, glycidyl methacrylate, maleic acid, or maleic anhydride.

12. The power cable according to claim 1, where the power cable further comprises an armouring laid around a cable core.

13. The power cable according to claim 12, where the armouring is one of: galvanized steel wires, steel tape, braid, sheath, or low loss armour.

14. The power cable according to claim 1, where the outer sheathing is made of a thermoplastic or a thermosetting material chosen from a polyvinyl chloride (PVC) or a chlorosulphanated polyethylene (CSP).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] FIG. 1 is a drawing seen from the side of a typical prior art three-phase power cable.

[0048] FIGS. 2a) and 2b) are drawings seen respectively from the side and front of a one-phase example embodiment of the power cable according to the invention.

[0049] FIGS. 3a) and 3b) are drawings seen respectively from the side and front of a one-phase example embodiment of the power cable according to the invention.

[0050] FIG. 4 is a drawing as seen from the front of an example embodiment of a three-phase power cable according to the invention.

DETAILED DESCRIPTION

First Example Embodiment

[0051] This example embodiment is a single phase power cable according to the first aspect of the invention which is schematically illustrated in FIGS. 2a) and 2b). FIG. 2a) is an exploded view of an end as seen from the side of the power cable and FIG. 2b) is a cut view as seen from the front.

[0052] The power cable 1 of this example embodiment has a reinforcement member 2 made of a bunt of austenitic steel wires of AISI 316 Stainless Steel (UNS S31600) at the centre. The steel wire is embedded in a layer 3 of aluminium wires of the AA1120 (UNS A91120) alloy constituting the electric conducting material. Then follows an electric insulation 4 of polyethylene (EP) and an outer sheathing 5 made of polyvinyl chloride (PVC). The cable core in this example embodiment consists of the reinforcement element 2, the electric conducting material 4 and the electric insulation 4.

[0053] FIGS. 3a) and 3b) illustrate a similar embodiment with the position of semiconducting conductor screen 4a shown.

Second Example Embodiment

[0054] This example embodiment of the power cable according to the first aspect of the invention is a three-phase submarine power cable illustrated schematically in FIG. 4). The figure is a cut view as seen from the front.

[0055] The power cable 1 of this example embodiment has three conductors, each consisting of a reinforcement element 2 made of a bunt of austenitic steel wires of AISI 316 Stainless Steel (UNS S31600) at the centre followed by a layer of aluminium wires of the AA1120 (UNS A91120) alloy constituting the electric conducting material 3. Then follows an electric insulation layer 4 of polyethylene (EP). In contrast to the conductor of the first example embodiment, the conductors of the second example embodiment also consisted of an inner sheathing/water barrier 6 made of a CuNiSi-alloy having a composition of from 0.8 to 30 weight % Ni, from 0.1 to 2 weight % Si, from 0.1 to 1.5 weight % Fe, and from 0.1 to 1.5 weight % Mn, based on the total mass of the alloy. The three conductors are held in place by distancing profiles 7 providing the cable core (which in this example embodiment comprises the three conductors and the distancing profiles) with a circular cross-section.

[0056] Outside of the cable core, the cable of this example embodiment has an armouring 8 of galvanized steel wires and an outer sheathing 5 made of polyvinyl chloride

[0057] Verification of the Invention

[0058] Numerical calculations have been carried out on embodiments according to the invention and comparison embodiments of 245 kV three-phase power cables to investigate the power loss (AC resistance).

[0059] The calculations were made by applying a two-dimensional modelling based on the Finite Element Method (FEM). The calculations accounted for both skin and proximity effects. The comparison embodiments include cables having non-hybrid conductors and cables having hybrid conductors but with reinforcing element (the steel phase) lying on the outside of the conducting material, i.e. an inverse configuration as compared to the hybrid conductor according to the invention which has the reinforcing element at the centre of the conductor.

[0060] Common to all example embodiments applied in the calculations is that each conductor had a first 1.5 mm thick semiconductive sheath laid onto the outer metal phase (either the current conducting material or the reinforcement element, depending on which of them being outside of the other), then followed a 22 mm thick insulation layer of XLPE (cross-linked polyethylene), a second 1.5 mm thick semiconductive sheath, and then a 2.2 mm thick lead sheath as water barrier. The current conducting material in all example embodiments was an aluminium alloy AA1120 (UNS A91120) defined to have a resistivity of 2.89766.Math.10.sup.−8 [Ohm-m] and a relative magnetic permeability of 1. The reinforcement element was either made of a carbon steel assumed to have a resistivity of 2.00.Math.10.sup.−7 [Ohm-m] and a relative magnetic permeability of 700, or made of AISI 316 Stainless Steel (UNS S31600) assumed to have a resistivity of 7.40.Math.10.sup.−7 [Ohm-m] and a relative magnetic permeability of 1. The carbon steel applied as comparison reinforcement element is a hypothetical carbon steel ally having electric and magnetic properties close to a G34-series carbon steel and is thus denote as G34 in table 1. In the model the cores are set to carry balanced three-phase current of 1000 A at 50 Hz. Upon solving the FEM-model, the current distribution between inner core material and the conductor material is determined. A conductor temperature of 90° C. is assumed.

[0061] Both the current conducting material and the reinforcing element in these example embodiments consisted of wires stranded together, the different configurations of the hybrid conductors applied in the calculations are summarized and the calculated AC resistivities are given in table 1:

TABLE-US-00001 TABLE 1 Configuration of wires in the conductors applied in the calculations Calculated Inner wires Outer wires AC Diam. # of Diam. # of resistivity Material [mm] wires Material [mm] wires [Ohm/km] Case 1 1120.sup.1) 4.10 91 — — — 0.0348 Case 2 G34.sup.2) 4.10 19 1120 4.10 72 0.04104 Case 3 SS316.sup.3) 4.10 19 1120 4.10 72 0.04077 Case 4 G34 2.08 62 1120 3.68 113 0.03348 Case 5 SS316 2.08 62 1120 3.68 113 0.03332 Case 6 1120 4.10 19 G34 4.10 72 0.04719 Case 7 1120 4.10 19 SS316 4.10 72 0.04169 Case 8 1120 2.08 62 G34 3.68 113 0.03768 Case 9 1120 2.08 62 SS316 3.68 113 0.03430 .sup.1)ASTM AA1120 aluminium alloy (UNS A91120) .sup.2)Carbon steel close to G34 series .sup.3)ASTM SS316 stainless steel (UNS S31600)

[0062] A comparison between the calculated AC resistances of case 1 of table 1 (a three-phase power cable having non-hybrid conductors of only aluminium AA1120 wires) and cases 4 and 5, shows that a hybrid conductor having the reinforcement element located at the centre of the conductors may attain a power loss being equal or somewhat less than the power loss of a pure aluminium conductor.

[0063] Table 1 informs further that otherwise equal configurations except for applying a magnetic or a low or non-magnetic steel as the reinforcing element, typically gives a difference in the AC resistivities of 0.4 to 0.6%. For example, the AC resistivity when applying a reinforcing element of SS316 (case 3) at the centre of the conductor is 0.49 percent less than the AC resistivity when applying a reinforcing element of carbon steel (case2). A similar result of 0.65% reduction in the AC resistivity when applying SS316 steel is obtained between cases 4 and 5. This verifies that there is somewhat less power loss when applying a low-magnetic or non-magnetic steel in the reinforcing element of the hybrid conductor according to the invention. Even though these figures may seem small, the accumulated power losses over the lifetime of the cable becomes considerable. A similar reduction of 0.5-0.6% in the AC resistivity is also observed for the “inverted” cases (the comparison example with the reinforcement element outside the current conducting aluminium wires).

[0064] A significantly larger difference between the AC resistivities (and thus the power loss) is observed when comparing the hybrid conductor according to the invention having the reinforcement element at the centre of the conductor with an “inverse” configuration where the current conducting wires are at the centre and the reinforcement element is laid onto the current conducting wires. The difference between the AC resistivities of e.g. cases 3 and 7, i.e. with SS316 steel at the core or on the outside is 2.25% when the steel is at the core. A comparison between cases 5 and 9 gives 2.9% reduction is the SS316 steel is located at the centre.

[0065] The results above show that there is a significant reduction in the power loss of three-phase power cables obtained by applying a reinforcing element of low magnetic or non-magnetic steel and locating it at the centre of the conductors.