JPH10285773A - Offset part of metal sheath plastic insulated power cable - Google Patents

Abstract

(57) [Problem] To reduce an axial force applied to a cable core on both sides of a connection portion due to thermal expansion of a power cable in an offset portion of a large-sized metal sheath plastic insulated power cable. SOLUTION: A part b- of the offset part near the connecting part 3 is provided.
(c) removes the metal sheath and covers the cable core with a moisture-proof pipe 19 having an inner diameter larger than the metal sheath and having good flexibility. The portion ab near the conduit opening 9 is maintained in a predetermined curved shape by the curved shape maintaining roller 17 while leaving the metal sheath as it is. The connecting portion 3 is supported so as to be movable at least in a direction perpendicular to the axis thereof. Thus, the extension of the cable core can be restricted, and the extension of the cable core can be absorbed by the internal space and the deformation of the moisture-proof pipe 19, so that the axial force can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an offset portion of an ultra-high voltage (large size) metal-sheathed plastic insulated power cable.

[0002]

2. Description of the Related Art FIGS. 3 and 4 show an offset portion of a conventional power cable. In the figure, 1 is a power cable, 3
Denotes a connection portion of the power cable 1, 5 denotes a manhole, 7 denotes a conduit into which the power cable 1 is drawn, and 9 denotes a conduit opening.

In the manhole 5, the connecting portion 3 and the conduit opening 9
A portion ab near the conduit opening 9 and a portion bc near the connection portion 3 of the power cable 1 between the two are curved in opposite directions to provide a slack called an offset.
This is to absorb the power cable 1 in the pipeline 7 extending into the manhole 5 due to thermal expansion. Note that the connection portion 3 of the power cable 1 is mounted on a metal receiving member 13 that extends horizontally from the standing metal member 11, and is fixed by a fixing bracket 15.

[0004] In recent years, ultra-high voltage CV cables (cross-linked polyethylene insulated power cables) have been increasing in size both in conductors and metal sheaths, and with this, the axial force generated in the cable core in the connection portion due to thermal expansion has also become extremely large. And the cable core may buckle in the connection box, making it impossible to maintain sufficient withstand voltage characteristics. For this reason, it is necessary to reduce as much as possible the axial force generated in the cable core in the connecting portion, particularly the axial force difference caused by the difference in axial force between the cable cores in the offset portions on both sides of the connection box.

[0005] In an ultra-high voltage CV cable (cross-linked polyethylene insulated power cable) having a metal sheath such as an aluminum sheath, the thermal expansion amount, longitudinal stiffness (EA) or bending stiffness (E) of the cable core (conductor and insulator) and the metal sheath.
I) governs the axial force during thermal expansion. The thermal expansion of the cable core is larger than that of the metal sheath, and conversely, the bending rigidity (EI) is larger in the metal sheath than in the cable core. As a result, in the offset portion as described above, of the expansion due to the thermal expansion of the cable core, the portion that extends extra than the metal sheath tends to cause the metal sheath to bend more than the bending deformation due to its own thermal expansion. Thus, the cable core receives a reaction force from the metal sheath side, and generates an extremely large axial force.

If the inner diameter of the metal sheath is extremely larger than the outer diameter of the cable core, and there is sufficient space to absorb the extra extension of the cable core in the metal sheath,
Since the axial force of the cable core is generated only by the bending rigidity of the cable core, the axial force is not so large.
However, it is necessary to keep the outer diameter of the power cable as small as possible from the viewpoint of handling and transport length, and usually, the clearance between the cable core and the metal sheath is 1-2.
Since only about mm is secured, in the offset portion, the cable core and the metal sheath must be substantially integrally deformed.

In order to minimize the axial force component caused by the bending stiffness (EI) of the metal sheath in the offset portion, the metal sheath of the offset portion is peeled off as disclosed in, for example, JP-A-6-70437. It is conceivable to substitute a flexible bellows tube. However, with this structure, the extension of the cable core from the pipeline side is almost unlimitedly added to the offset part, so even if the axial force of the cable core is reduced by reducing the reaction force from the metal sheath, The result is that the axial force reduction effect is offset by the axial force increase due to the increase in the amount.

An object of the present invention is to provide an offset portion capable of reliably reducing an axial force applied to a cable core at a connection portion of a metal-sheathed plastic insulated power cable in view of the above problems.

[0009]

SUMMARY OF THE INVENTION In order to achieve this object, the present invention is to provide a power supply system comprising a metal sheath plastic insulated power cable connection portion in a manhole and a pipe port, the portion being close to the connection portion of the power cable. In the offset portion of the metal-sheathed plastic insulated power cable in which the portion near the road entrance is curved in the opposite direction, the portion near the connection portion has the inner diameter larger than the metal sheath by removing the metal sheath, and is larger than the metal sheath. The cable core is covered with a flexible moisture-proof pipe, and a portion near the conduit opening is held in a predetermined curved shape by a curved shape holding member while leaving a metal sheath as it is. .

[0010] With this configuration, the cable core is covered with the flexible moisture-proof pipe having a larger inner diameter than the metal sheath in the portion near the connection portion of the offset portion. The extended portion can be absorbed by the internal space and the deformation of the moisture-proof pipe, and the axial force of the cable core can be reduced. Further, in the portion of the cable offset portion near the conduit opening, the metal sheath held in a curved shape by the curved shape holding member acts as resistance against extension of the cable core, so that extension of the cable core can be limited. Therefore, the effect of reducing the axial force of the cable core by the moisture-proof pipe can be further ensured.

In the offset portion of the present invention, it is desirable that the connection portion of the power cable be supported so as to be movable at least in a direction perpendicular to the axis thereof. This makes it possible to further reduce the axial force of the cable core.
Further, it is desirable that the curved shape holding member in the present invention holds the power cable movably in the bending direction. Further, in the present invention, it is desirable that the joint between the metal sheath and the moisture-proof pipe is located near the inflection point where the bending direction of the power cable changes.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention. The metal sheath CV cable 1 from the conduit opening 9 of the manhole 5 to the connecting portion 3 is a portion a near the conduit opening 9.
-B is curved with a radius R _1, the connecting portion 3 side of the portion b
−c is curved to the opposite side with a radius R ₂ to form an offset portion.

In such an offset portion, a portion ab near the conduit opening 9 of the CV cable 1 has a large number of rollers in order to increase resistance to the extension of the metal sheath CV cable 1 from the conduit 7 side. 17 and metal sheath C
It is assumed that the V cable 1 is held in a curved shape. a-b
Since the metal sheath CV cable 1 is held by the rollers 17, it can move in the bending direction, but since the curved shape is fixed by the rollers 17, a large resistance force against extension is obtained. Occur.

FIG. 2 shows 500 kV × 2500 mm ² CV
When the cable is held by a roller so as to draw an arc with a radius of 5000 mm, the relationship between the roller installation interval (arc angle between the rollers) and the reaction force when the cable is pushed toward the connection part was numerically analyzed. The results are shown. According to this, it is understood that the reaction force (corresponding to the resistance to the extension of the cable) increases exponentially as the interval between the rollers becomes smaller. Accordingly, the interval θ at which the rollers 17 are installed may be set to 20 ° or less, preferably 15 ° or less.

On the other hand, the portion bc near the connecting portion 3 of the CV cable 1 has the metal sheath removed at the time of the connection work, and the cable core of this portion has a larger inner diameter than the metal sheath and a smaller diameter than the metal sheath. The moisture-proof metal pipe 19 having good flexibility is covered with the moisture-proof property. Generally, a corrugated aluminum sheath or a stainless steel sheath is used as the metal sheath of the metal sheath CV cable 1, and the corrugated height of the metal sheath is about several mm, and the clearance between the metal sheath and the cable core is 1-2 mm. Set to about. On the other hand, a corrugated metal pipe 1 to be placed between bc
Reference numeral 9 denotes a large-diameter one that can secure a clearance of 50 mm or more from the cable core. It is also possible to use a corrugated plastic pipe instead of the corrugated metal pipe 19.

At both ends of the corrugated metal pipe 19, flanges 21 and 23 are attached. One flange 21 is joined to a flange 25 fixed to the end of a metal sheath by a lead work, and the other flange 23 is connected. Box flange 27
Is connected via packing. Corrugated metal pipe 19
Has a certain degree of elasticity, so that when the connecting portion 3 is formed, it may be contracted so as not to hinder the connecting operation. It is preferable that the joint between the flanges 21 and 25 be located near the inflection point b which is a reversal part of the bending direction in order to reduce the ironing of the cable core at the end of the metal sheath.
There is not much problem even if it is slightly away from the inflection point b.

The connecting portion 3 is supported by a roller 29, and the roller 29 is slidable along a shaft 31 in a direction perpendicular to the axis of the connecting portion 3. Thereby, the connecting part 3 can be moved both in the axial direction and in the direction perpendicular to the axis. By doing so, the effect of reducing the axial force of the cable core is further enhanced. Even if the connecting part 3 cannot be moved in the axial direction, it is perpendicular to the axis (direction of the axis 31).
It is effective to increase the effect of reducing the axial force if it can be moved.

Next, a cable behavior analysis by the finite element method is performed by assuming a model line in which the cable extends unevenly into the manhole from the pipes on both sides, and the conventional offset part and the offset part of the present invention are analyzed. Table 1 shows the results of calculating the axial force difference between the cable cores on both sides of the connection portion and the maximum distortion value of the offset portion.

[0019]

[Table 1]

As is apparent from the results, the offset portion of the present invention can greatly reduce the difference in axial force applied to the cable core of the connection portion, and can reduce the difference to an allowable level (1000 kg) or less. Although the maximum distortion of the offset portion of the present invention is larger than that of the conventional offset portion, it is sufficiently small and safe compared to the allowable level (1%), and there is no problem in practical use. In the offset portion of the present invention, the junction box moves laterally, but the amount is small, and there is no problem such as insufficient manhole dimensions.

In the above embodiment, the case where the roller is used as the curved shape holding member has been described. However, the cable is fixed to the curved shape (actually, the metal sheath) by using the cleat instead of the roller. It is also possible.

[0022]

As described above, according to the present invention, since the entire cable core is held in a curved shape by the curved shape holding member at the portion of the offset portion near the conduit opening,
A large resistance is generated against the extension of the cable core, and the extension of the cable core can be restricted. In addition, the portion of the offset portion near the connection is removed by removing the metal sheath and covering it with a flexible, moisture-proof pipe that has a larger inside diameter than the metal sheath, so that the cable core extends more than the metal sheath due to thermal expansion. This can be absorbed by the internal space and deformation of the moisture-proof pipe. As described above, the offset portion of the present invention is combined with the fact that the extension of the cable core is limited, and the extra extension of the cable core from the metal sheath can be absorbed by the internal space and deformation of the moisture-proof pipe. Thus, the axial force applied to the cable cores on both sides of the connection portion can be reliably reduced.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of an offset unit according to the present invention.

FIG. 2 is a graph showing the relationship between the installation interval of rollers when a CV cable is held in an arc shape by a roller, and the reaction force against the pushing of the cable.

FIG. 3 is a front view of a conventional offset unit.

FIG. 4 is a sectional view taken along line AA in FIG. 3;

[Explanation of symbols]

 1: power cable 3: connection part 5: manhole 7: conduit 9: conduit opening 17: roller 19: corrugated metal pipe 29: roller 31: shaft

Claims (4)

[Claims] 1. A metal having a portion near a connection portion and a portion near a conduit opening of the power cable between the connection portion of the metal-sheathed plastic insulated power cable and the conduit opening in the manhole in opposite directions. In the offset portion of the sheath plastic insulated power cable, the portion closer to the connection portion, the metal sheath is removed, the inner diameter is larger than the metal sheath, and the cable core is covered with a moisture-proof pipe that is more flexible than the metal sheath, The offset portion of the metal-sheathed plastic insulated power cable, wherein the portion near the conduit opening is held in a predetermined curved shape by a curved shape holding member while leaving the metal sheath as it is. 2. The offset part according to claim 1, wherein the connection part of the power cable is supported so as to be movable at least in a direction perpendicular to its axis. 3. The power supply apparatus according to claim 1, wherein the holding member holds the power cable movably in the bending direction.
Or the offset part of 2. 4. The offset part according to claim 1, wherein a joint between the metal sheath and the moisture-proof pipe is located near an inflection point where the bending direction of the power cable is reversed.