JP4801236B2 - High voltage DC power cable and its submarine cable laying method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to high voltage direct current (HVDC) cables and methods for laying such cables on the sea floor. Such a cable and its laying method are described in WO 97/04466 (G Barlog 13).
[0002]
[Prior art]
UK 2295506 describes an HVDC system in which a rectifier and a plurality of converters are connected by a DC link, and the arc extinguishing angle of the inverter is used to control the firing angle of the rectifier in the closed loop. The arc extinguishing angle of is maintained at a predetermined value or more. Each converter has a closed loop controller that controls the firing angle of the rectifier in response to the direct current, the direct current voltage, the extinguishing angle of the converter itself, and the firing angle of the converter itself.
[0003]
DE1262425 relates to a device for "voltage suppression (VOLTAGEWISE RELIEF)" of cables in the HVDC installation method, in which both ends are connected to an AC network via "smoothing" coils and rectifiers, and also to supply and receive power The alternating current network and the associated rectifier are such that the number of phases on the alternating current side at both ends does not include the same prime number.
[0004]
The usual way to transfer energy from one location to another across a body of water, such as between Norway and Denmark, is to use HVDC cable with a central insulated conductor and use seawater for return current It is. This cable is laid between AC circuits having the same number of phases. One alternative is to lay another HVDC cable in parallel with the first cable for the return current. This is an expensive solution.
[0005]
[Problems to be solved by the invention]
The object of the present invention is to provide a new cable and a new laying technology, which is a reliable, high-energy long-distance transfer between two locations separated by water bodies at a reasonable cost. To meet the requirements of
[0006]
[Means for Solving the Problems]
The main features of the invention are defined in the claims. With these solutions, the Applicant has succeeded in satisfying customer requirements. Applicant's cable operates in monopolar mode without having an external magnetic field. This laying method eliminates seawater electrodes that can cause high costs and a wide range of environmental problems.
[0007]
The above and other features and objects of the present invention will become apparent from the following detailed description of the embodiments of the present invention taken together with the drawings.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a cross-sectional view of a cable, showing a central core with one or more layers of insulating material 2 encapsulated within a metal sheath. The inner and outer semiconductor layers respectively disposed on the surface of the core wire 1 and the lower side of the lead sheath 3 are not shown. In the lead sheath, an insulator sheath 4, a reinforcing material 5, an exterior 6, an insulator 7, an exterior 8, and an outer protective layer 9 are continuously arranged.
[0009]
The conductor 1 is a multi-wire copper conductor. The insulator 2 may be a tape-wrapped or extruded insulator. The metal sheath 3 is a conventional lead alloy sheath. The first layer 4 covering the metal sheath is a polymer such as polyethylene (PE). This first layer can be a semiconductor to avoid or reduce the potential difference. A lateral reinforcement 5 such as a stainless steel tape is arranged on the surface of the layer 4. Next, the two-layer exterior 6 which is a hard copper wire with a profile is arranged. Next, an insulator sheath 7 which is a PE sheath, an exterior 8 made of galvanized steel wire, and an outer protective material 9 made of polypropylene yarn and asphalt are disposed.
[0010]
For a cable capable of transferring 800 MW at 500 KV through a submarine cable route greater than 500 Km, the center conductor should have a cross-sectional area of 1.600 mm ² and the return conductor should be approximately 1.900 mm ² in length. Should have an area. This cable should preferably be buried at the seabed, preferably at a depth of 2.5 m from the seabed.
[0011]
FIG. 2 schematically shows main components (conductor 1, return conductor 6, and sheath 8) disposed between two terminal stations A and B. Stations A and B include a converter (not shown) for interconnection with an AC network (not shown). Conductor 1 transfers cable current from A to B, and sheath 8 is continuously grounded. The coaxial return conductor 6 is connected to ground potential through surge arresters (valves) 10 and 11 located at both ends of the cable, and the return conductor is grounded midway between A and B. This grounding is performed by a semiconductor material.
[0012]
The metal return conductor must be grounded so that there is no circulating current. At the same time, the converter must be true grounded. The circulating current is divided according to resistance in different loops. Since seawater can be considered a very large conductor, only the resistance of the lead to the electrode, the resistance of the electrode, and the final resistance at the ground will define the loop resistance.
[0013]
3, the laying method is the same as the laying method of FIG. 2, but in this alternative example, one end (A end) of the return conductor 6 is grounded, and the other end (B end) is the surge arrester (valve) 12. Connected to the ground through.
[0014]
In a cable having a metal return conductor, a DC voltage of about 10 kV is applied over a length of 540 km at a load of 800 MW. Resistors can be used to limit the ground current, but this is not desirable when there is a ground current. Another way is to prevent circulating currents by a single point connection. This method is possible if one of these valves needs to be grounded directly, but at the other end, 10 kV is applied to the other valve group on the ground side.
[0015]
When the cable system is grounded in the middle (FIG. 2), a DC voltage of about 5 kV is applied to both valve groups on the ground side. In this case, at both ends, the diode can be used as a Zener diode, and the outer insulator can be protected from overvoltage.
[0016]
The above detailed description of the embodiments of the invention is to be understood as illustrative only and should not be taken as limiting the scope of protection.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a cross section of an HVDC cable.
FIG. 2 is a diagram illustrating an example of a cable laying method.
FIG. 3 is a diagram illustrating an example of a cable laying method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Core wire, Conductor 2 Insulation material, Insulator 3 Lead sheath 4 Insulator sheath, 1st layer 5 Reinforcement material, Layer 6 Exterior, Return current conductor 7 Insulator, Insulator sheath 8 Exterior 9 Outer protection layer, Outer protection material

Claims (5)

High-voltage direct current comprising a central conductor (1) and an insulator layer (2) covered with a metal sheath (3) such as a lead sheath and covered with an outer exterior layer (8) and an outer corrosion protection layer (9) A power cable having a polymer insulator (or semiconductor) layer (4), a reinforcing material (5), a copper sheath serving as a return conductor (6), and at least one additional outside the metal sheath (3) The outer sheath layer (8) is disposed on the at least one additional polymer insulator layer (7), and the outer corrosion protection layer (9) is disposed on the outer sheath layer. Disposed on the layer (8), the return conductor (6) comprising the metal sheath (3) and the at least one such that the at least one additional polymer insulator layer (7) surrounds the return conductor (6). 1 additional polymer insulator layer High voltage DC power cable, characterized in that disposed between the 7).   The high-voltage DC power cable according to claim 1, characterized in that the polymer insulator layer (4, 7) is a polyethylene layer.   The outer exterior layer (8) is continuously grounded along the cable route between the end connection A and the end connection B, and the return conductor (6) is connected to the end connection (A, B). The submarine cable laying method for a high-voltage DC power cable according to claim 1 or 2, characterized in that it is grounded in the middle. The return conductor is, in addition to being grounded in the middle of the end connection portions (A, B), and characterized in that it is also grounded through both ends (A, B) surge arrester (10, 11) arranged in The cable laying method according to claim 3.   The outer sheath layer (8) is continuously grounded along the cable route between the end connection A and the end connection B, the return conductor (6) is directly grounded at one end (A side), and The method for laying a submarine cable for a high-voltage DC power cable according to claim 1 or 2, wherein the other end (B side) is grounded through a surge arrester (12).

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