JPH0216088B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for regulating the bending of offset cables in power cable lines.

Background of the Invention Generally, cables are laid in a 300 to 400 m long conduit and connected inside a manhole. Provide an offset section.

The amount of cable extension into the manhole is generally calculated to be 100 to 200 mm, which is absorbed by bending the offset cable.

In actual offset design, in order to make the offset dimension as small as possible, the bending radius of the cable at the offset portion after absorbing the amount of extension is designed to be close to the allowable value (for example, 10 times the outer diameter of the cable).

However, in the actual thermal behavior of the cable at the offset section, due to the cable's unique elastoplastic deformation, the calculation does not go as planned, and the bending of the cable is concentrated in one part, causing the bending radius to exceed the allowable value (for example, 10 times the outer diameter of the cable). ) The following parts will appear.

If the cable is repeatedly bent to a radius that is less than the allowable value, the metal insulation layer will be damaged, and if this damage extends toward the cable insulation, there is a risk of dielectric breakdown.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for regulating the bending of a cable at an offset portion, which allows the bending radius of the cable to always be kept above a permissible value.

Structure of the Invention As shown in FIGS. 1 and 2, the bent portion of the offset cable 30 has a rigid, bell-mouth shape that is thinnest at the center in the length direction and gradually widens toward both ends. A plurality of bend regulating pipes having flanges 14 are connected with each other with play between the brim 14 and always covered; the spacing g between the flanges on the outside of the bending of the adjacent regulating pipes is set. It is characterized in that the bending radius of the bending portion cannot become less than a preset tolerance value by preventing the bending portion from opening beyond a value.

Configuration description FIG. 1 shows an example of the bending regulating pipe 10.

It is made of a light yet mechanically strong material, such as aluminum alloy. The main body 12 has a substantially cylindrical shape, but more precisely, it has a bellmouth shape, which is narrowest at the center in the longitudinal direction and gradually widens toward both ends. Main body 1
A collar 14 is provided at both ends of 2. Numeral 18 is a bolt hole for connecting the bending regulating pipes 10 to each other. This whole thing is divided into two parts, and one bolt
6 for combinatorial connection.

How to attach the bending regulation tube 10 (Fig. 2) Wrap a rubber sheet 32 or the like around the cable 30 so that the outer diameter is approximately equal to the inner diameter of the bending regulation tube 10, and cover it with the bending regulation tube 10 split in half. Connect with bolts 16.

For example, three bend regulating pipes 10 are arranged side by side in contact with each other. Then bolt 20 at the 4 locations on the collar 14.
are passed through the bolt holes 18 and connected to each other. However, at that time, a gap (play) should be created between the nut 22 (or bolt head) and the collar 14.

The distance between the nut 22 and the bolt head is set as follows. That is, when the cable 30 is bent and the bending radius gradually becomes smaller, the flanges 14 of the adjacent bend regulating tubes 10 become gradually narrower on the inside of the bend, and the tops 14a of the flanges 14 finally come into contact with each other, and the bending radius gradually becomes smaller. On the outside, it opens until there is a gap between the flanges 14 of adjacent bending regulating pipes 10, but beyond that point the nut 22 and the bolt head act as a stopper, making it impossible to open any further. Set. In this case, even if the cable 30 tries to bend any further, the movement is restricted by the bending restriction tube 10, so that the cable 30 cannot bend any further.

Note that the bending radius at which the cable 30 cannot be bent any further is set to a value slightly larger than the allowable value (for example, in the case of a cable whose allowable bending radius is 10 times the outer diameter of the cable, 11x).

Mounting position of bending regulation pipes 10 A plurality of bending regulation pipes 10 are connected and mounted at a location where the bending radius is expected to be the minimum. usually,
The bending radius will be minimum at the lowest point of the cable after the amount of extension has been absorbed, so the cable should be installed centered at that point. It goes without saying that the offset portion may be attached over the entire length of the cable.

However, the position of the lowest point where the cable hangs down the most is different between horizontal offset and diagonal offset.

(i) In the case of horizontal offset (Fig. 3) Offset part cable 30 after absorbing the extension amount
The center of the actual length of is the lowest point. In other words, from the center point of the initial offset, a position closer to the conduit 34 by half the amount of cable extension is set as the center.
Attach the bending regulation pipe 10.

(ii) In the case of diagonal offset (FIG. 4) For example, if the conduit 34 is lower than the junction box 36, the lowest point of the cable 30 will be closer to the conduit 34 than the center of the offset cable.

In both cases (i) and (ii) above, once the bending regulating pipe 10 is installed, it can be further moved to an appropriate position based on the behavior of the cable 30.

Test results ●Cable: 77kV, 3000mm ² CV cable ●Offset type: Horizontal (Figure 3) ●Cable outer diameter: 115mm ●Offset length L: 2700mm ●Length of bending regulation pipe 10: 250mm ●Diameter of collar 14: 190mm ●Cable extension amount: Under conditions of 160mm or more, bend the three bending control pipes 10 at a position 80mm closer to the conduit 34 from the initial offset center point of the cable 30 as shown in Figure 2. Installed. At that time, adjustments were made so that there was a gap g of 40 mm on the outside of the bend.

As a result, the minimum bending radius was 11 times the outer diameter of the cable, and the amount of deflection d (Figure 3) was 395 mm.

On the other hand, if there is no bending regulation pipe 10,
The minimum bending radius was 8 times the outer diameter of the cable, and the amount of deflection d was 405 mm.

Another example of the bending regulation pipe 10 (Fig. 5) One collar 14 is the same as the one above, but
The other brim 15 is wide and has an outward rising portion 1.
5a and an inward facing collar 15b. When the collar 14 of the adjacent regulating pipe 10 is fitted into the collar 15 as shown in the figure, the same effect as the connection using the bolt 20 described above can be obtained.

Effects of the invention (1) A plurality of bend regulating tubes having flanges at both ends are always covered over the bent portion of the offset portion cable by connecting the flanges with play between them; By making sure that the spacing between the ribs on the outside of the bend of the regulating pipe does not exceed a set value, the bending radius of the bent portion cannot become less than a preset allowable value. As mentioned above, since the ribs 14 can be connected to each other with bolts or the like, attachment to the cable is very easy.

Furthermore, when bolts are used to connect the flanges 14, it is very easy to change the set value of the spacing g between the flanges on the outside of the bend.

(2) The bend control pipe is rigid and has a bell mouth shape that is narrowest at the center in the length direction and gradually widens towards both ends, so the inside of the bend of multiple control pipes connected is continuous and smooth. Since it is arc-shaped and there are no corners that protrude, localized force is not applied to the cable.

[Brief explanation of drawings]

The drawings are all related to the present invention; Fig. 1 is an explanatory diagram showing the side and front sides of the bending regulation pipe 10 at the same time, Fig. 2 is an explanatory diagram of how to attach the bending regulation pipe 10, and Fig. 3 is a horizontal offset diagram. 4 is an explanatory diagram of diagonal offset, and Fig. 5 is an explanatory diagram of bending regulation pipe 1.
0 is an explanatory diagram of another example. 10: Bending control tube, 14: Collar, 20: Bolt, 30: Cable.

Claims (1)

[Claims] 1 Offset part At the bending part of the cable; a plurality of bend regulating tubes, which are rigid and have a bell mouth shape that is thinnest at the center in the length direction and gradually widens toward both ends, and have ribs at both ends, are installed between the ribs. are connected with some play between them and are always covered; by making sure that the spacing between the ribs on the outside of the bends of adjacent regulating pipes does not exceed a set value, A method for regulating bending of a cable at an offset portion, characterized in that the bending radius cannot be less than a preset allowable value.