EP1999761A1

EP1999761A1 - Power cable capable of detecting failure

Info

Publication number: EP1999761A1
Application number: EP06716522A
Authority: EP
Inventors: Dae Kyeong Kim; Hee Seok Ryoo; Sang Bong Choi; Sung Hwan Jeong; Ki Young Nam; Jae Duk Lee
Original assignee: Korea Electrotechnology Research Institute KERI
Current assignee: Korea Electrotechnology Research Institute KERI
Priority date: 2006-03-24
Filing date: 2006-03-24
Publication date: 2008-12-10
Also published as: JP2009531826A; WO2007111389A1; EP1999761A4

Abstract

Disclosed herein is a power cable capable of detecting failure. The power cable in accordance with one embodiment of this invention includes a conductor, and an auxiliary line which is inserted into an inner layer provided between the conductor and an outermost layer and is installed to extend in a longitudinal direction in a spiral arrangement. The auxiliary line is made of an optical fiber, and the thickness of the auxiliary line is determined so that the auxiliary line is cut or deformed by a force sufficient to cause damage to the power cable. Preferably, pitch of the auxiliary line is 30mm or less. Further, the inner layer corresponds to an anti-corrosive layer which is formed to protect against external impact or corrosion, or a polyethylene sheath which covers an insulator covering the conductor.

Description

D E S C R I P T I O N

POWER CABLE CAPABLE OF DETECTING FAILURE

1 . Technical Field

The present invention relates generally to a power cable capable of detecting failure and, more particularly, to a power cable, which is constructed to allow a location at which external or internal failure of various kinds of power cables for transmitting or distributing power occurs to be easily found.

2. Background Art As well known to those skilled in the art, a power cable used for transmitting or distributing power has considerably long ground distribution lines or ground transmission lines extending to a plurality of spots where power is used, so that the arrangement of the power cable is complicated. Recently, as accidents and environment problems are firstly considered, there has been a growing tendency for the power cable to be buried under the ground in downtown areas or in specific regions requiring a good appearance. An OF cable or an XLPE cable has been widely used as the underground transmission line, and an XLPE cable has been widely used as the underground distribution line.

When such a power cable is used as a ground distribution line or a ground transmission line, the power cable is apt to be damaged by natural disasters or external impacts. Further, when a transmission line or a distribution line forms an underground line, it may be easily damaged by accidents or corrosion upon deterioration with age.

As such, when the power cable is damaged and fails, the supply of power ceases. Moreover, unless the fault is fixed in a timely manner, extensive injury to people and vast physical damage are caused by the fault.

A conventional power cable is designed to satisfy only electrical requirements, without considering the method of easily determining a failure location when there is a problem with the power cable.

In the prior art, for dealing with the method of pinpointing a failure location in a conventional cable, various methods, such as a Murray Loop Test, Capacitive Discharge Fault Location, Time Domain Reflectometer (TDR) , and Arc Reflection Method (ARM) , have been developed. However, the methods have a drawback in that it is difficult to efficiently find a failure location, due to the structural restriction of the conventional power cable.

Thus, the development of a power cable, which is capable of enabling easy pinpointing of a failure location while sufficiently satisfying electrical requirements for the power cable, has been keenly needed.

Further, a submarine cable is a power cable which couples the land to an island or couples islands to each other. An insulated cable filled with insulating oil has been mainly used as the submarine cable. However, it is problematic in that the cable may fail due to an external impact, such as an anchor of a ship or a trawl of a trawl boat, or a defect in the cable.

The conventional submarine cable is designed to satisfy only the electrical requirements required for the submarine cable. However, a method of easily finding a failure location in the submarine cable has not been realized yet.

According to the prior art, in order to find a failure location in a submarine cable, a method of applying a signal to a cable conductor and receiving the signal on the sea has been mainly used. However, the method is problematic in that it is difficult to efficiently find a failure location, due to structural limitations of the submarine cable. Therefore, the development of a power cable or submarine cable, which is capable of enabling easy finding of a failure location while sufficiently satisfying electrical requirements for the power cable or submarine cable, has been keenly needed. 3. Disclosure of Invention

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a power cable or a submarine cable capable of helping the detection of failure, which is constructed to enable rapid and easy determination of a failure location.

In order to accomplish the above object, the present invention provides a power cable including a conductor, and an auxiliary line inserted into an inner layer provided between the conductor and an outermost layer, and installed to extend in a longitudinal direction in a spiral arrangement.

In this embodiment, the power cable is a transmission line or a distribution line which carries power underground. The power cable is a submarine power cable which carries power in the sea.

The inner layer corresponds to an anti-corrosive layer formed to protect against external impact or corrosion, or a polyethylene sheath which covers an insulator covering the conductor. And, the auxiliary line is inserted between several layers forming the inner layer of the power cable.

The auxiliary line is made of an optical fiber, and preferable a plastic optical fiber. The thickness of the auxiliary line is determined so that the auxiliary line is cut or deformed by a force sufficient to cause damage to insulator covering the conductor, and it is preferable that the thickness of the auxiliary line is 2mm or less.

Further, laser light is applied to the auxiliary line continuously, or at regular intervals, or intermittently, so as to detect failure of the power cable, and a failure location of the power cable is detected based on time it takes for reflection waves, reflected from the failure location where the auxiliary line is^' broken, to reach a location where the laser light is applied.

4. Brief Description of Drawings

The accompanying drawings, which are included to provide a further understanding of the invention, illustrate the preferred embodiments of the invention, and together with the description, serve to explain the principles of the present invention.

FIG. 1 is a cross-sectional view showing a power cable capable of detecting failure, according to the first embodiment of the present invention;

FIG. 2 is a view showing the state where an auxiliary line for detecting failure is installed in the power cable according to the present invention;

FIG. 3 is a view representing experimental stress test results of the auxiliary line for detecting failure, according to the present invention; FIG. 4 is a view illustrating the state where the auxiliary line for detecting failure according to the first embodiment of this invention is cut due to damage to the power cable;

FIG. 5 is a view showing the connected state of the auxiliary line for enabling detection of the failure or determining a failure location of the power cable, according to the first embodiment of the present invention; and

FIG. 6 is a cross-sectional view showing a submarine power cable capable of detecting failure, according to the second embodiment of the present invention. Features, elements, and aspects of the invention that are referenced by the same numerals in different figures represent the same, equivalent, or similar features, elements, or aspects in accordance with one or more embodiments. 5. Modes for Carrying out the Invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view showing a power cable capable of enabling detection of failure, according to the first embodiment of the present invention.

As shown in FIG. 1, the power cable according to the first embodiment of this invention includes a conductor 10 which has a predetermined thickness and carries power to the central portion of the power cable. The conductor 10 is covered with an insulator

20. A sheath 30 is provided on the outer portion of the insulator

20 to cover the insulator 20. Further, an anti-corrosive layer

40 having a predetermined thickness is provided on the outer portion of the sheath 30 to cushion external impacts and prevent corrosion.

Referring to the drawing, an auxiliary line 50 for detecting failure is inserted into the anti-corrosive layer 40 in such a way as to extend in the same direction as the conductor 10. As shown in FIG. 2, the auxiliary line 50 is installed to extend in a regular spiral shape along the longitudinal direction of the corresponding power cable, thus detecting the failure along the entire power cable.

In the case where the auxiliary line for detecting failure is installed parallel to the longitudinal direction of the power cable, the auxiliary line may not be damaged or cut when a portion having no auxiliary line, as seen in a cross section of the power cable, is damaged. In order to solve the problem, according to the present invention, the auxiliary line is installed to extend in the longitudinal direction of the power cable in a regular spiral arrangement.

However, if the auxiliary line is a wire, such as an enameled wire, the spiral arrangement increases reactance, thus hindering the flow of electric current in the auxiliary line. That is, if the wire is installed in a spiral arrangement, transmission loss is increased. Thereby, closed-circuit detectors for detecting the location of defects must be installed at much smaller intervals . According to this invention, in order to solve the problem, the auxiliary line is made of an optical fiber which has very low transmission loss. The optical fiber serves to transmit light, for example laser light, output from a light source. When the optical fiber is deformed or damaged, the intensity, phase, polarization, and wavelength of light passing through the optical fiber are changed. Such variation is detected by a photo-detector. According to this invention, when an optical fiber breaks, the location where the optical fiber breaks can be detected using the time it takes for laser light to be reflected from the broken fiber portion.

Further, when the spiral pitch of the auxiliary line is long, the auxiliary line may not be damaged. In this case, damage to the cable may not be detected. Conversely, when the spiral pitch of the auxiliary line is short, the length of the auxiliary line to be used in the power cable is increased. Thus, it is desirable that 154kV OF cable or XLPE cable having a diameter of 10cm to 12cm have a spiral pitch of 3cm or less.

In order to monitor failure due to damage to the power cable, laser light is applied from a light source to the auxiliary line 50, comprising an optical fiber, continuously, or at regular intervals, or intermittently. Further, the thickness of the auxiliary line 50 is determined so that the auxiliary line 50 is easily cut or deformed as a result of impact when cable is damaged by external impacts or internal factors. The auxiliary line 50, made of an optical fiber, is inserted into the anti-corrosive layer 40 of the power cable. Displacement deforming the sheath 30 by a pressure of 50 bar acts on the anti-corrosive layer 40 as loading conditions thereof. In such a state, the results obtained from changing the diameter of the auxiliary line 50 inserted into the anti-corrosive layer 40 are represented in FIG. 3.

Referring to FIG. 3, when the thickness of the optical fiber is 2mm or less, the stress applied to the optical fiber after the sheath is damaged is larger than the tensile strength of the optical fiber, that is, 6.7kgf/mm2. This means that the auxiliary- line made of the optical fiber is damaged when the power cable is damaged. Thus, it is preferable that the thickness of the optical fiber be 2mm or less.

FIG. 3 shows the fracture characteristics according to the thickness of the optical fiber used as a material of the auxiliary- line 50. Using the fracture characteristics, it is possible to appropriately adjust the thickness and pitch of the optical fiber according to the characteristics of the installation position of the power cable or the surrounding environment.

Owing to the progress of technology, a reduction in the thickness of the power cable can be achieved. In proportion with the reduced thickness of the power cable, the spiral pitch and/ or the thickness of the optical fiber, which is the auxiliary line, are reduced. Such a tendency has been verified through experimentation and analysis.

The auxiliary line 50 for detecting failure may be inserted into the anti -corrosive layer 40. Alternatively, the auxiliary line 50 may be inserted between layers forming the power cable, such as between the insulator 20 and the sheath 30 or between the sheath 30 and the anti-corrosive layer 40.

Further, the optical fiber used as the auxiliary line 50 for detecting failure may be made of glass or plastic. According to this invention, it is more preferable that the auxiliary line comprises an optical fiber made of plastic, which has higher ductility.

The operation of detecting the failure location in the power cable, according to the first embodiment of this invention, will be described in detail with reference to FIGS. 4 and 5.

First, the auxiliary line 50 is installed in the anti-corrosive layer 40 of the power cable in such a way as to extend spirally along in the longitudinal direction of the corresponding power cable. In such a state, as shown in FIG. 5, laser light is applied from a light source in the light detectors 70, installed at regular intervals of the power cable, to the auxiliary line 50. As shown in FIG. 5, each of the light detectors 70 includes a light source which generates laser light or the like that is transmitted through the auxiliary line 50, a photo-detector which detects reflection waves reflected from the broken auxiliary line, and a calculation unit which calculates the failure location using the time difference between application of the laser light and arrival of the reflected waves. Further, each light detector 70 may also include a communication module which informs a server, which is provided at a remote position and controls the condition of the power cable, of the detected failure location. The light source of each light detector 70 generates light, for example, laser light, having an intensity that can be transmitted to and reflected from a subsequent light detector, and applies the generated light to the auxiliary line 50.

If the power cable is damaged due to external or internal factors, as shown in FIG. 4, the auxiliary line 50 of a failure location 60 is broken due to impact.

When the auxiliary line 50 breaks at the failure location 60 of the power cable, an associated portion of the auxiliary line 50 is opened. Using the reflection waves reflected at the open portion, the open state and the open location caused by the breakage of the auxiliary line 50 may be detected at the light detectors 70, installed at regular intervals of the power cable, as shown in FIG. 5. The second embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 6 is a cross-sectional view showing a submarine power cable capable of detecting failure, according to the second

5 embodiment of the present invention.

As shown in FIG. 6, the submarine power cable according to the second embodiment of this invention includes a conductor 80 which has a predetermined thickness and carries power to the central portion of the power cable. The conductor 80 is covered

10 with an insulator 82. A polyethylene sheath 84 is provided on the outer portion of the insulator 82 to cover the insulator 82.

Armor 86 is installed outside the polyethylene sheath 84 to protect the cable against external impact. Further, an outer sheath 88 having a predetermined thickness is provided outside

15 the armor 86.

Referring to the drawing, an auxiliary line 90 for detecting failure is inserted into the polyethylene sheath 84 and extends in the same direction as the conductor 80. The auxiliary line

90 may be inserted between the polyethylene sheath 84 and the armor

20 86 or between the armor 86 and the outer sheath 88.

Like the auxiliary line 50 according to the first embodiment, the auxiliary line 90 is installed in such a way as to extend in a regular spiral shape along the longitudinal direction of the corresponding submarine cable, thus detecting failure along the 25 entire length of submarine power cable.

In order to monitor failure due to damage to the submarine power cable, laser light is applied from a light source to the auxiliary line 90 continuously, or at regular intervals, or intermittently. Further, it is preferable that the auxiliary line 30 90 is made of an optical fiber, for example a plastic optical fiber having a thickness of 2mm or less so that the auxiliary line 90 is easily cut due to impact when the polyethylene sheath 84 of the cable is damaged by external impacts or internal factors. The operation of detecting the failure location in the submarine power cable, according to the second embodiment of this invention, will be described in detail with reference to FIG. 6.

First, the auxiliary line 90 is installed in the polyethylene sheath 84 of the submarine cable in such a way as to extend spirally in the longitudinal direction of the corresponding submarine cable. In such a state, laser light is applied to the auxiliary line 90.

If the submarine cable is damaged due to external or internal factors, the auxiliary line 90 of a failure location is broken due to impact .

When the auxiliary line 90 breaks at the failure location of the submarine cable, an associated portion of the auxiliary line 90 is opened. Using the reflection waves reflected at the open portion, the open state and the open location caused by the breakage of the auxiliary line 90 may be detected at light detectors, installed at regular intervals of the submarine cable.

As described above, the present invention has the effect of enabling rapid detection of a failure location in a power cable or a submarine cable .

Although the preferred embodiments of the present invention have been disclosed 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.

Claims

C L A I M S

1. A power cable, comprising: a conductor; and an auxiliary line inserted into an inner layer provided between the conductor and an outermost layer, and installed to extend in a longitudinal direction in a spiral arrangement.

2. The power cable as set forth in claim 1, wherein the power cable is a transmission line or a distribution line which carries power underground.

3. The power cable as set forth in claim 1, wherein the power cable is a submarine power cable which carries power in the sea.

4. The power cable as set forth in claim 1, wherein the inner layer, into which the auxiliary line is inserted, corresponds to an anti -corrosive layer formed to protect against external impact or corrosion.

5. The power cable as set forth in claim 2, wherein the inner layer, into which the auxiliary line is inserted, corresponds to an anti-corrosive layer formed to protect against external impact or corrosion.

6. The power cable as set forth in claim 1, wherein the inner layer, into which the auxiliary line is inserted, corresponds to a polyethylene sheath which covers an insulator covering the conductor .

7. The power cable as set forth in claim 3, wherein the inner layer, into which the auxiliary line is inserted, corresponds to a polyethylene sheath which covers an insulator covering the conductor.

8. The power cable as set forth in claim 1, wherein the auxiliary line is inserted between several layers forming the inner layer of the power cable.

9. The power cable as set forth in claim 1, wherein the auxiliary line is made of an optical fiber.

10. The power cable as set forth in claim 9, wherein the optical fiber is made of plastic.

11. The power cable as set forth in claim 9, wherein a thickness of the auxiliary line is determined so that the auxiliary line is cut or deformed by a force sufficient to cause damage to the power cable.

12. The power cable as set forth in claim 11, wherein the thickness of the auxiliary line is 2mm or less.

13. The power cable as set forth in claim 9, wherein laser light is applied to the auxiliary line continuously, or at regular intervals, or intermittently, so as to detect failure of the power cable.

14. The power cable as set forth in claim 13, wherein a failure location of the power cable is detected based on time it takes for reflection waves, reflected from the failure location where the auxiliary line is broken, to reach a location where the laser light is applied.

15. The power cable as set forth in claim 1, wherein a pitch of the auxiliary line is 30mm or less.