JPH0557804B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a power cable line in which cross-bonding is performed without using an insulating junction box.

(Technical background of the invention and its problems) When transmitting power through a power cable line, it is necessary to reduce the metal sheath current induced by the conductor current in order to increase the power transmission capacity.

Conventionally _, in a power cable line in which three metal-sheathed single-core power cables ₁ are installed in parallel as shown in FIG. A normal connection NJ is formed at , and the metal sheaths at this normal connection and cable heads A and B are grounded by a grounding wire L, and the cable lengths l ₁ and l ₂ of each cross bond section are l ₁ /3 or l Insulated connection parts IJ are formed at positions equally divided into small sections of _2/3 each, and each metal sheath end at the front and rear of these insulated connection parts is connected to the metal sheath end of the other phase cable.
By cross-bonding each phase using a cross-bond wire C, sheath current induced in each phase cable sheath is canceled out.

However, in actual cable lines, the installation points of junction boxes that form normal connections and insulated connections are restricted by the cable installation route, so insulated connections are placed at positions that divide each cross bond section into three equal parts. IJ cannot often be installed. In such a case, the sheath current of each phase cable cannot be canceled out, and a large circulating current flows through the sheath circuit.

In addition, the metal sheath of each phase cable has insulated connections.
It is electrically disconnected before and after the IJ, and this becomes the surge impedance mutation point, so if a surge voltage such as an opening/closing surge or external lightning enters the cable, the metal sheath and the ground will connect at the above mutation point. An excessive voltage was generated during this period, and there was a risk that the anti-corrosion layer provided on the outer surface of the metal sheath would be destroyed.

(Objective of the Invention) The present invention has been made to eliminate the above-mentioned drawbacks in the background art, and it is possible to cross-bond at any position without using a large and expensive insulating junction box, and to prevent surge voltage from entering. To provide a power cable line whose anti-corrosion layer is not destroyed even when the corrosion occurs.

(Summary of the invention) The power cable line of the present invention is provided with a shielding layer having relatively high electrical resistance as a metal shielding layer, an external conductor is provided on the outside of the shielding layer via a light insulator, and an anti-corrosion layer is further provided on the outside of the shielding layer. Using a power cable, cut portions were formed in the outer conductor of each phase cable at the cross bond points, and one end of the outer conductor before and after these cut portions was sequentially cross-bonded to the other end of the outer conductor of the other phase cable. The main feature is that.

(Embodiments of the invention) Hereinafter, embodiments of the invention will be described with reference to the drawings.

FIG. 2 is a cross section showing an embodiment of the power cable used in the present invention, and the power cable 1
is a main insulating layer 1 on the outer surface of the cable conductor 1a.
b, metal sheath 1c, floor layer 1d, outer conductor 1
e, and a corrosion protection layer 1f are sequentially provided. The main insulating layer is made of oil-impregnated insulating paper, crosslinked polyethylene, etc., and semiconductive layers (not shown) are provided on the inner and outer surfaces thereof.

The metal sheath 1c is constituted by a corrugated sheath made of a material such as stainless steel which does not have very high conductivity and therefore has low eddy current loss and is formed into a threaded tube shape. In addition, the seat layer 1d provides light insulation between the metal sheath 1c and the outer conductor 1e.
It is constructed by wrapping thin insulating paper or tape so that the dielectric strength value ranges from 200V to several KV.

The outer conductor 1e is made by winding or vertically attaching multiple annealed copper wires or copper tapes on the floor layer 1d. For example, in the case of a cable with a voltage of 154KV class, the diameter is 1.2
65 mm diameter annealed copper wires are used, and for 275KV class cables, approximately 80 2 mm diameter annealed copper wires are used. In addition, when using a copper tape as an external conductor, it is desirable to prevent adjacent tapes from directly overlapping each other in order to reduce eddy current loss.

The power cable line of the present invention is constructed by arranging three of the power cables 1 described above in parallel as shown in FIG. 3, and connecting them at the normal connection part NJ in the middle. The outer conductor 1e of each phase cable has a cross-bond section l1 from cable head A to normal connection NJ and _a cross-bond section _l2 from this normal connection to cable head B at the other end, respectively, approximately _l1 /3. or
It is cut at positions divided into three small sections of l ₂ /3 to form cut parts 2, and before and after these cut parts, cross bonds are sequentially made to the external conductor 1e of the other phase cable using cross bond wires C. has been done.

The metal sheath 1c and the outer conductor 1e of the power cable line are electrically connected to each other in three phases at a normal connection part NJ, and are grounded as necessary. Further, the metal sheath 1d and the outer conductor 1e of each phase cable are grounded by a grounding wire L at the connection point between the cable heads A and B, respectively.

In addition, when connecting the external conductor 1e to the normal connection part NJ, cross bond wire C, and ground wire L,
The terminals of the conductor strands constituting the outer conductor are collectively connected by a bind wire wound around the outer periphery or by soldering.

Next, the operation of the power cable line configured as above will be explained.

When three-phase alternating current is passed through conductor 1a of each phase cable,
Eddy current and sheath current flow through the metal sheath 1c due to electromagnetic induction. However, in the present invention, the metal sheath is made of stainless steel or the like, which has a lower electrical conductivity than copper or aluminum, so the eddy current and sheath current are small.

In addition, three-phase AC induced voltage is also generated in the external conductor 1e due to the electromagnetic induction described above, but these induced voltages are canceled by the cross bonds between the three power cables, so almost no voltage is applied to the external conductor. No current flows. Also, the eddy current generated in the external conductor is extremely small.

On the other hand, when the cable 1 undergoes dielectric breakdown, the seat layer 1d having a low dielectric strength voltage also breaks down and becomes conductive, so that the fault current flows into the ground through the external conductor 1e.

When a surge voltage enters the cable due to opening/closing of a switch or external lightning, a surge current flows through the metal sheath 1c. However, since the frequency is a high frequency on the order of several hundred KHz to several MHz, the surge current is transferred to the metal sheath 1 due to the skin effect.
It will flow along the inner surface of c. As a result, the electromagnetic field caused by the surge current is shielded by the metal sheath 1c, and only a small amount leaks to the outside, so that almost no surge current flows through the outer conductor 1e. Therefore, even if the cross bond point of the external conductor 1e becomes a surge impedance variation point, an abnormal voltage will not occur there and destroy the corrosion protection layer 1e.

In the above explanation, we have described an example in which a stainless steel corrugated sheath is used as the metal shielding layer, which allows the propagation of intruding surges, has a shielding effect against high frequencies, and has low eddy current loss. Any appropriate material or structure may be used. For example, the material may be a low-conductivity copper alloy or aluminum alloy, and the structure may be a braided layer, a wrap layer of tape, or a vertical layer.

Further, the light insulator does not necessarily need to be the above-mentioned floor layer, but may be a thin insulating layer that covers each conductor strand constituting the external conductor. Further, the material may be a semiconductive material as long as it has an appropriate resistance value. However, when using a semiconducting material, it is desirable that the material has a resistance value of several kilohms or more per meter in the length direction of the cable, considering the loss caused by the current flowing therein and the effect on the external conductor.

Furthermore, the above-mentioned cross-bond section is not limited to between cable heads and ordinary connection parts, but may be between cable heads or between ordinary connection parts.

In addition, if the single length of the cable is shorter than the length of the cross bond section due to manufacturing or transportation reasons, a normal junction box is installed at an appropriate point within the cross bond section to connect the cable. In that case, the normal junction box shall be ungrounded. Furthermore, it is not necessary to ground the shielding layer and the external conductor at each end of the cross bond section, but it may be done only at the cable head or only at one location within the other cross bond section.

In addition, it is most preferable to provide the cutting part (cross bond point) of the external conductor at a position that divides the cross bond section into three equal parts in order to cancel the sheath current, but if there is a reason for the installation route, it is not necessary to divide the cross bond section into three equal parts. It does not have to be installed in the same position.

(Effect of the invention) As described above, in the power cable line of the present invention,
A power cable is provided with a main insulation layer and a low conductivity metal shielding layer on the outside of the cable conductor, an external conductor is provided on the outside of this metal shielding layer via a light insulator, and a corrosion protection layer is further provided on the outside of the power cable. Since the cross-bonding is made only on the outer conductor, it is possible to cross-bond at any position without using an expensive and large insulating junction box, and the anti-corrosion layer will not be destroyed even if surge voltage penetrates. .

Furthermore, in the case of tunnel installation, cross-bonding is possible at points other than manholes, making it easy to set cross-bonding points and reducing sheath current.

Furthermore, since the outer conductor has a wire structure, the eddy current generated in the outer conductor can be reduced, and the metal shielding layer, which is the inner shielding layer, and the outer conductor are connected at a position corresponding to a normal connection in a cross bond. Because the phases are connected together, the metal shielding layer, which is the internal shielding layer, does not need to be at ground potential;
The number of interconnections can be reduced.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a cross-bond system using a conventional cable, FIG. 2 is a sectional view of a power cable according to the present invention, and FIG. 3 is an explanatory diagram of a power cable line according to the present invention. 1... Power cable, 1a... Cable conductor,
1b...Main insulating layer, 1c...Metal sheath, 1d...
... Seat layer, 1e... External conductor, 1f... Corrosion protection layer,
2... Cutting section.

Claims (1)

[Claims] 1 A main insulation layer and a low-conductivity metal shielding layer are provided on the outside of the cable conductor, and a wire-structured outer conductor is provided outside of this metal shielding layer via a low-conductivity insulator, and an anticorrosion layer is further provided on the outside of this metal shielding layer. Three power cables configured with a
In addition to connecting the phases all at once, cut portions are formed in the outer conductor at positions that approximately divide the cross bond section into thirds, and one end of each outer conductor at these cut portions is connected to the cut portion of the other phase cable. A power cable line characterized by successive cross-bonding to the outer conductor on the end side.