WO2008093926A1

WO2008093926A1 - Protecting tube for very high pressure cable

Info

Publication number: WO2008093926A1
Application number: PCT/KR2007/006155
Authority: WO
Inventors: Sung-Yun Kim; Jeong-Nyun Kim; Sung-Ik Sim; Mi-Kyung Ahn
Original assignee: Ls Cable Ltd.
Priority date: 2007-02-02
Filing date: 2007-11-30
Publication date: 2008-08-07
Also published as: KR100773696B1

Abstract

The present invention relates to a protecting tube for a high voltage cable, and more particularly to a protecting tube for a cross-linked polyethylene (XLPE) cable joint box capable of sufficiently resisting damage due to short current and internal pressure and external force through the provision of optimum designing condition. The protecting tube for high voltage cable comprising a main body and an end part with a minimum cross-sectional area formed at one end of the main body, wherein the minimum cross-sectional area sufficient to resist a capacity of the short-circuit current is calculated by following the equation 2 (in case where the tube is Cu tube) being Y=0.126X, and the equation 3 (in case where the tube is Al tube) being Y=0.086X, where, Y is a short-circuit current capacity, and X is a cross-sectional area of the protecting tube.

Description

Description PROTECTING TUBE FOR VERY HIGH PRESSURE CABLE

Technical Field

[1] The present invention relates to a protecting tube for a high voltage cable, and more particularly to a protecting tube for a cross-linked polyethylene (XLPE) cable joint box capable of sufficiently resisting damage due to short current and internal pressure and external force through the provision of optimum designing condition. Background Art

[2] In general, a protecting tube for high voltage XLPE cable joint box, as illustrated in

FIG. 1, comprise a metallic main body 11, such as Al or Cu material, having an outer surface of a PVC layer 12. The main body 11 is provided with a circumferentially protruding grounding terminal 13 and an end part 14 having a minimum cross- sectional area at one side thereof.

[3] Since such a protecting tube 10 should have a structure which prevents the occurre nee of damage in cable due to short-circuit current and resists a certain internal pressure and an external force. Therefore, upon designing, requirements to satisfy allowable short-circuit current according to materials and structural strength should be considered. If a cross section of a protecting tube is not properly designed, it is likely to damage the PVC layer 12 due to heat, which may mainly cause degradation in electrical performance and corrosion of the protecting tube.

[4] A cross-sectional area sufficient to resist heat generated by short circuit should be secured in order to prevent above mentioned problems. However, a conventional protecting tube has much greater or smaller cross-sectional area, since there is not the design reference. Therefore, economical, functional losses of a conventional protecting tube occur.

[5] Further, in case of insufficient structural strength in the protecting tube 10, there is a problem in that cable or the like in the proteting tube 10 may be damaged due to an external force.

Disclosure of Invention Technical Problem

[6] The present invention has been made to solve the problems occurring in the prior art, and an object of the present invention is to provide an economical and functional protecting tube for high voltage cable by providing a proper design reference for a minimum cross-sectional area and a thickness of the protecting tube. Technical Solution

[7] In order to accomplish the above and other objects of the present invention, there is provided a protecting tube for high voltage cable comprising a main body and an end part with a minimum cross-sectional area formed at one end of the main body, wherein the minimum cross-sectional area sufficient to resist a capacity of the short-circuit current is calculated by following equations 2 and 3, the equation 2 (in case where the tube is Cu tube) being Y=O.126X, and the equation 3 (in case where the tube is Al tube) being Y=0.086X, where, Y is a short-circuit current capacity, and X is a cross- sectional area of the protecting tube.

[8] Further, when the short-circuit current capacity (Y) is 12OkA in the equations 2 and

3, the minimum cross-sectional areas of the Cu protecting tube and the Al protection tube are 952mm and 1400mm , respectively.

[9] In accorance with another aspect of the present invention, there is provided a protecting tube for high voltage cable comprising a main body and an end part with a minimum cross section formed at one end of the main body, wherein the protecting tube has a thickness with enough structural strength by following equation 4, the equation 4 being In(Y)=- 1.24In(X)+ 1.76, where Y is an equivalent stress, and X is a thickness of the protecting tube.

[10] Further, in order to meet the requirements of the structural strength, when safety factor is 1.5, and a respsting pressure reference is 3kgf/cm , the thicknesses of the Al protecting tube and the Cu protecting tube are of 3 to 8mm and 2 to 6mm, respectively.

Advantageous Effects

[11] This invention provides proper design references to calculate the minimum cross- sectional area sufficient to resist a capacity of the short-circuit current and the thickness of the protecting tube with enough structural strength, respectively, so that it prevents damage of the cable due to short-circuit current, and resists certain internal pressure and external force. Brief Description of the Drawings

[12] FIG. 1 is a schematic perspective view illustrating a structure of a conventional protecting tube for cable;

[13] FIG. 2 is a graph showing an allowable current capacity relative to a cross-sectional area for the respective materials in order to design a protecting tube for high voltage of the present invention; and

[14] FIG. 3 is a graph showing correlation between a stress and a thickness of the protecting tube for high voltage cable satisfying an internal pressure reference. Mode for the Invention

[15] Hereinafter, the construction and effects of a protecting tube for high voltage cable according to the present invention will be described with reference to accompanying drawings. [16] FIG. 2 is a graph showing an allowable current capacity of the cross-sectional area depending on the respective materials in order to design the protecting tube 10 for high voltage cable. Basically, the protecting tube 10 should have a cross-sectional area sufficient to resist a capacity of the short-circuit current and the thickness of the protecting tube with enough structural strength. Thus, first, a cross-sectional area which is sufficient to resist a capacity of the short-circuit current and depending on the respective materials is calculated by following equation.

[17] Equation 1

[18] I ²t=K²S²In[(θ +β)/(θ +β)]

AD f i

[19] Herein, I is short-circuit current, t is duration of short-circuit, K is a constant

AD depending on the material, S is a geometrical cross-sectional area, θ is initial temperature, θ is final temperature, and β is a reciprocal of temperature coefficient.

[20] In order to calculate a minimum cross-sectional area of the protecting tube 10, a short-circuit current capacity of an end part 14 having a minimum cross-sectional area among the portions that upon occurrence of accident, may be a current path is cauculated, the final temperature is fixed to 200⁰C according to equation 1 to determine the short-circuit current capacity because the temperature generated upon the accident is preferably designed to 200⁰C or less to prevent a PVC layer 12 from being damaged, and then the corresponding short-circuit current capacity and cross-sectional area are calculated, thereby providing a designing reference of the protecting tube 10 for high voltage cable according to the present invention. 12OkA can be adopted as the designing reference in consideration of the safety factor to be about 2, although most of currently available high voltage system has no system above 6OkA.

[21] Meanwhile, since there is a difference between the Al and Cu protecting tubes having minimum cross-sectional area sufficient to resist a capacity of the short-circuit current, the allowable current capacities of the cross-sectional area depending on the respective materials can be calculated and shown in the graph of FIG. 2.

[22] Herein, when the short-circuit current capacity of designing reference is determined to be 12OkA, the protecting tube 10 for high voltage cable satisfies the following equation depending upon the material, i.e., Cu and Al.

[23] In case of Cu tube:

[24] Equation 2

[25] Y=0.126X, and

[26] In case of Al tube:

[27] Equation 3

[28] Y=0.086X

[29] Herein, Y is a short-circuit current capacity (kA), and X is a cross-sectional area

(mm ). [30] When the short-circuit current capacity is determined to be 12OkA by the equations

2 and 3, the minimum cross-sectional areas of the protecting tube 10 are respectively 952mm² for Cu tube and 1400mm² for Al tube.

[31] Meanwhile, FIG. 3 is a graph showing a stress of the protecting tube calculated by structural analysis (Finite Element Analysis) at an internal pressure reference of 3kgf/cm . When an experiment was done under the condition where an element network is formed using a 3D shell element having a thickness through modeling for the same actual shape. Further, elestic modulus and Poisson's ratio of the Cu and Al materials are used as inherent physical properties, and internal pressure of 3kgf/mm . In this case, protecting tube as an operating load, it could be known that a maximum stress for the thickness of 3mm was 1.52kgf/mm . Comparing this with an allowable strength (2.5kgf/mm for Al, and 4.5kgf/mm for Cu), it can be seen that the calculated stress has a suffucient strength. From the above, as shown in the graph of FIG. 3, the stresses occurring for the respective thicknesses are calculated and compared with the allowable strength to show, and the correlation between the stress and the thickness of the protecting tube can be shown in following equation 4.

[32] Equation 4

[33] In(Y)=-1.24In(X)+1.76

[34] Herein, Y is an equivalent stress (kgf/mm ), and X is a thickness (mm) of the protecting tube.

[35] Since stresses on the graph of FIG. 3 should be respectively equal to or lower than the allowable strengths for the materials of Al and Cu tubes, it is preferable that considering the safety factor to be 1.5, the Al tube be of a minimum thickness of 3mm or more, and the Cu tube be of a minimum thickness of 2mm or more.

[36] Meanwhile, as shown in Table 1, the thickness ranges of the Al and Cu tubes according to the satisfactions to the short-circuit capacity and the structural strength, and assembly are preferably of 3 to 8mm and 2 to 6mm, respectively.

[37] Table 1

[38] [39] Although the exemplary embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

[40]

Industrial Applicability [41] The protecting tube for high voltage cable according to the present invention has the minimum cross-sectional area sufficient to resist a capacity of the short-circuit current and the thickness of the protecting tube with enough structural strength, to thereby prevents the damage of the cable due to cable short-circuit current and resists certain internal pressure and external force.

Claims

[1] A protecting tube for high voltage cable comprising: a main body; and an end part with a minimum cross-sectional area formed at one end of the main body, wherein the minimum cross-sectional area sufficient to resist a capacity of the short-circuit current is calculated by following equations 2 and 3, the equation 2 (in case where the tube is Cu tube) being Y=0.126X, and the equation 3 (in case where the tube is Al tube) being Y=0.086X, where, Y is a short-circuit current capacity, and X is a cross-sectional area of the protecting tube.

[2] The protecting tube for high voltagge cable according to claim 1, wherein when the short-circuit current capacity (Y) is 12OkA in the equations 2 and 3, the minimum cross-sectional areas of the Cu protecting tube and the Al protection tube are 952mm and 1400mm , respectively.

[3] A protecting tube for high voltage cable comprising: a main body; and an end part with a minimum cross section formed at one end of the main body, wherein the protecting tube has a thickness with enough structural strength by following equation 4, the equation 4 being In(Y)=- 1.24In(X)+ 1.76, where Y is an equivalent stress, and X is a thickness of the protecting tube.

[4] The protecting tube for high voltage cable according to claim 3, wherein when safety factor is 1.5, and a respsting pressure reference is 3kgf/cm , the thicknesses of the Al protecting tube and the Cu protecting tube are of 3 to 8mm and 2 to 6mm, respectively, in order to meet the requirements of the structural strength.