JPH05184027A - Power cable laying method - Google Patents

Abstract

PURPOSE:To provide an electrically and mechanically highly reliable laying method by removing occurrence of nonuniformity in the radius of a circular arc, which constitutes the shape of a line in laying, or a small partial bend, in the snake laying method for a power cable in a trough or a pit. CONSTITUTION:For the shape of the zigzag in the method of laying a power cable zigzag in a curved route, circular arcs AC, which inscribe the outside periphery of the width of laying, and circular arcs CE, which circumscribe the inside periphery of the width of laying, are constituted continuously, and the radius Rc of each circular arc is the same, and the length of the circular arc AC inscribing the outside periphery of the width of laying is longer than that of the chord of the circular arc CE circumscribing the inside periphery of the width of laying, and besides at the junction between each circular arc, both circular arcs AC and CE contact with each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of laying a power cable in a cave having a bend.

[0002]

2. Description of the Related Art One of the methods for laying a power cable is to lay a cable in a meandering shape. This is generally called snake laying, and is often used for laying in FRP troughs installed like shelves in caves and pits installed in trenches on the ground surface. ..

By the way, the caverns, pits, etc. are usually formed in a straight line or a curved line having a very large bending radius (r). First, a method of laying a straight trough will be described with reference to FIG. As shown in the figure, if a serpentine line with width B and length L is installed on both sides of the snake center line so that it fits inside the trough, the bend radii of the cable that draw the arc of the upper chord and the arc of the lower chord with the center line as the boundary. Becomes R, and becomes a meandering shape with a good balance.

On the other hand, there is a case where the bending radius (r) is unavoidable when the installation route is restricted as in the case of installation in a curved trough. In such a case, there are mainly the following cable laying lines.

As shown in FIG. 4, the cable can be housed in the trough by laying the cable meandering along the bend of the trough. However, even if the length L of the chord of each arc drawn with the center line of the snake is the same, the width is B ₁ , B
_Since it is different from ₂ , the corresponding bending radius also differs depending on each arc such that R ₁ <R ₂ and it is not preferable.

FIG. 5 shows an improvement of this method and the same bending radius. The bending radii R are different in the laying line of FIG. 4 because the widths B ₁ and B ₂ are different even if the chord length L is the same. Therefore, if the snake center line is shifted to the upper side of the drawing and laid as shown in FIG. 5, each width B and bending radius R can be made equal. However, as is clear from the figure, the points where the arcs are connected (inflection points)
As a result, the cable will bend, and the continuity of the laying line will be lost. The nonuniformity of R and the generation of locally small R (generation of a bent portion) as described above have a problem that the electrical and mechanical reliability of the cable is deteriorated. Therefore,
SUMMARY OF THE INVENTION It is an object of the present invention to provide a laying method that can prevent unevenness of R or the occurrence of locally small bent portions in the snake laying method and can prevent a decrease in reliability of the cable.

[0006]

In order to achieve the above object, the method of laying a power cable according to the present invention is such that the radii of arcs are the same and the cable is not bent at the contact points of these arcs. .. The feature is in the method of laying the power cable in a meandering shape on the curved route,
In the meandering shape, arcs inscribed in the outer circumference of the laying width and arcs circumscribing the inner circumference of the laying width are alternately and continuously formed, and the radii of the respective arcs are the same, and the chord of the arc inscribed in the outer circumference of the laying width. Is longer than the chord length of an arc circumscribing the inner circumference of the laying width, and both arcs are in contact with each other at a contact point of each arc. The laying width is a width that takes into account the thermal expansion of the cable and a slight margin, and refers to the width between the center of the cable in the meandering shape.

[0007]

The operation of the present invention will be described with reference to FIG. The figure shows the linear shape when a cable is laid in a meandering shape in a curved trough (route). This meandering shape consists of a succession of upper and lower chord arcs with the same radius (R).
The arc of the upper chord is in contact with the inner circumference of the installation width, and the arc of the lower chord is in contact with the outer circumference of the installation width. Then, the points where the two arcs are connected (inflection points) share a tangent line with each other. In this way, since it is composed of arcs having a uniform bending radius, and the continuity thereof is a laying line without bending, it is possible to eliminate the unevenness of the radius R and the occurrence of locally small bent portions. Cable laying with high mechanical and electrical reliability can be performed.

[0008]

EXAMPLE A meandering shape design by the laying method of the present invention will be described below with reference to FIG. First, the neutral axis S of the laying width is drawn at the radius Rt, and the inner and outer circumferences of the laying width that are the allowable laying width W (or a predetermined width that is smaller than the allowable width) are drawn. Next, a convex arc with a radius Rc is drawn so as to be inscribed at the point B on the outer circumference of the laying width. Then, this time, a downwardly convex arc is drawn with the same radius Rc so as to contact both the inner circumference of the laid width and the upwardly convex arc. As a result, the convex arc of the inner angle theta ₁ above, Sadamari the convex arc of the inner angle theta ₂ below, A, is also determined E. When the points A and E are determined, the inner angle φ of the meandering shape that forms one cycle by the continuation of the arcs AC and CE is determined,
A meandering shape is formed by continuing this cycle.

By determining the laying line in this manner, the arc AC inscribed in the outer circumference of the laying width and the arc CE circumscribing the inner circumference of the laying width are alternately and continuously formed, and the chord of the arc inscribed in the outer circumference of the laying width. Is longer than the length of the chord of an arc circumscribing the inner circumference of the laying width, and both arcs can be formed so as to be in contact with each other at the contact point C of each arc. That is, the arc AC and the arc CE share the tangent line with each other at the point C. Then, if the cable is dropped along the formwork in the trough made according to the laying line and after laying after determining the line shape of the cable, the radius Rc of the arc is uniform and a locally small bent portion is generated. It is possible to perform electrical and mechanically reliable laying without doing so.

[0010]

As described above, according to the laying method of the present invention, the radii of the arcs forming the meandering shape are the same, and the continuation of the arcs is performed without bending. It is possible to perform electrical and mechanically reliable laying without applying a cable.

[Brief description of drawings]

FIG. 1 is a schematic view of a meandering shape according to the laying method of the present invention.

FIG. 2 is an explanatory view of a meandering shape designing method in the laying method of the invention.

FIG. 3 is an explanatory diagram of a snake laying method in a straight trough.

FIG. 4 is an explanatory view of a conventional snake laying method in a curved trough.

FIG. 5 is an explanatory diagram of a conventional snake laying method in a curved trough.

[Explanation of symbols]

H Center of the arc that draws the neutral axis with the inner radius Rt F Center point of the arc AC G Center point of the arc CE A, E Start point and end point of one cycle of meandering shape B Arc and laying width Outer contact point D Arc and laying width Circumferential contact point C Arc contact point between arc AC and arc CE θ ₁ Inner angle of arc AC θ ₂ Inner angle of arc CE φ Meandering shape Inner angle formed by arcs of installation width corresponding to one cycle W Allowed cable installation width Rt Installation width Neutral axis Radius Rc Radius of arcs AC and CE S Neutral axis of laying width

Claims (1)

[Claims] 1. A method of laying a power cable in a meandering shape on a curved route, wherein the meandering shape is formed by alternately connecting arcs inscribed in the outer circumference of the laying width and arcs circumscribing in the inner circumference of the laying width. , The radius of each arc is the same, the length of the chord of the arc inscribed in the outer circumference of the laying width is longer than the length of the chord of the arc circumscribing the inner circumference of the laying width, and both arcs are the connecting points of each arc. A method of laying a power cable, characterized in that the two are in contact with each other.