JPS5973812A - Power cable and its defect detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to synthetic insulated cables for transmitting electrical power, particularly at high voltages.

BACKGROUND OF THE INVENTION Defects in cables transmitting power at high voltages, for example 200 kV, can have dangerous consequences. There is thus a need to create cables with extra wide safety margins.

Defects are caused in particular by excessive heating and the action of water on the insulation.

Abnormal temperature rises can be caused by a variety of causes, the most common being; accidental overloading of the power distribution array in undesirable environments such as cables being placed in close proximity to heating ducts or loose heat dissipation. It takes;
and the bond between the cables that constitute the thermal barrier. Under certain conditions, such abnormal heating can reduce the thickness of the composite insulator. Various techniques are used to combat the effects of moisture and >L degrees on cable insulation. Particularly good protection can be provided by arranging the cable inside the conductor sheath. However, such sheaths are quite heavy and expensive. Another similar technique is to insert the cable within an aluminum sheath. However, such sheaths are not always satisfactory. Furthermore, care must be taken to prevent water transmission in case of an accidental puncture.

The present invention provides an insulated electrical cable that does not require extra safety margins.

SUMMARY OF THE INVENTION The improvement of the cable according to the invention includes embedded within the cable over its entire length at least one optical fiber that is sensitive to temperature and/or moisture fluctuations and at least one end of which is sensitive to temperature and/or moisture fluctuations. This lies in the fact that it can be connected to a device that detects or measures humidity or its fluctuations. , the transmission coefficient of light along an optical fiber, the passband of the transmitted light and the refractive index of the material that makes up the optical fiber are all temperature dependent, and excess heating will reduce the transmission coefficient, passband and refractive index of the optical fiber. A detectable variation occurs, and such variation can be used to trigger an alarm.

Such cables can be continuously monitored and repaired before an accident occurs and breaks the circuit.

To detect moisture, an optical fiber can be placed next to a material that expands when wet.

Moisture, which does not affect the material at a particular point, causes the material to deform relative to adjacent unaffected material, causing a corresponding deformation of the optical fiber that contacts the expanding material.

Such deformations create strains in the optical fiber, which cause variations in the propagation of light transmitted by the light guide (U.S. Pat. No. 416
(See No. 3397). These propagation variations can be measured and used to trigger alarms as described in the aforementioned US patents.

In one embodiment, each optical fiber is disposed between a semiconductor screen surrounding an insulator and an aluminum-like metal screen surrounded by a protective sheath. In the case of detecting moisture here, a tape-shaped water-expandable element is placed around the periphery of the semiconductor, and an optical fiber is placed along said element below the screen. If the metal screen is made of composite material, i.e. consists of longitudinal wires with an aluminum-like metal sheath or tape surrounding the screen wire, each optical fiber is placed close to the screen wire. has been done.

DETAILED DESCRIPTION In FIGS. 1 and 2, the cable has a central conductor 1 for transmitting power surrounded by a layer 2 of a first semiconductor. The layer 2 is itself surrounded by a skin of synthetic insulator 2, which in turn is surrounded by a layer 4 of a second semiconductor.

A tape 5 of a material that expands when in contact with water is wrapped around the second semiconductor layer 40 .

A composite screen is arranged around the tape 5. The screen has conductors 6 and 6 parallel to the cable axis.
It has an aluminum sheath 7 surrounding it.

Finally, the sheath 7 is protected by an insulating outer device.

According to the invention, light guides 9 and 10, such as optical fibers, are arranged between the tape 5 and the metal sheath 7. The light guide, like the conductor 6, extends along the entire length of the cable and is connected at its end to a detector or alarm device (not shown).

The fiber 9 is adapted to detect excess cable heating. For this reason, one end is connected to the emitter and the other end is (
(not shown) is connected to a light receiver, and is capable of detecting fluctuations in the transmission coefficient and/or the passband of the received light, and triggers an alarm when excessive fluctuations are detected. The detector device is disclosed, for example, in French Painting Patent No. 2400195.
It may be of the type listed in the item.

The optical fiber light guide 10 is used to detect moisture at a predetermined point on the cable. Therefore, its termination can be used to measure variations in the light transmitted from one end of the fiber to the other to detect strains, pressures, and small displacements of the fiber, as described in U.S. Pat. No. 4,163,397. When the water penetrates the cable through the arrow mark 11 and reaches the tape 5, the wetted part 12 of the tape expands, while the adjacent part retains its original volume.Thus, the fiber 10 (see FIG. 3), and can be detected as described above.

The arrangement shown in FIG. 4 can be used to detect defects in the cable, both in the case of overheating and in the case of moisture ingress. A laser emitter 20 generates a light beam 21, which is directed into the light guide 9 or 1o at one end of the cable. Unavoidable microscopic defects within the fiber light guide are
The light is returned by back-diffusion, which is transmitted to the light emitter 20 of the cable.
The light is detected by the light receiver 22 located at the same end.

The graph of FIG. 5 shows the time ± plotted along the X-axis and the optical power P detected by the receiver 22 and returned plotted along the X-axis. Curve 24 is the response of ray 21 of the light pulse. Curve 24 decays exponentially. The beginning of the curve 24, near the origin 0, corresponds to the light returned from the part of the fiber close to the emitter 2o, and the end of the curve (near the X-axis) corresponds to the light returned by the part of the fiber far from the emitter 2o. Compatible with light.

That is, each point along curve 24 corresponds to a particular point on the cable.

If a defect occurs at a particular point exposed to the cable, whether due to heat or moisture, the light emitted by the laser emitter 20 will
Attenuation occurs at defects, which is manifested as a sharp drop in the power of the returned light. The point of descent 250 along the X-axis corresponds directly to the defect location along the cable.

If the refractive index of the optical fiber string changes due to a failure, the effect can be measured using the configuration shown in FIG. It is based on the Mahatswe/Da interferometer.

The measuring device has another optical fiber 30 of the same length as the optical fiber contained within the cable 23, but in such a way that the cable itself is not exposed, i.e. the same risks of overheating and moisture as the cable. are arranged to avoid

Besides another optical fiber 30, the device includes a laser emitter 20, the light output of which is divided into two parts by a device 31, such as a semi-transparent mirror, one of which is directed to the end of the cable 23 and the other is directed to the adjacent end of another fiber 30.

At the other end of the cable 23 and fiber 30, a coupling device 32, such as a second semi-transparent mirror, recombines the two parts of the transmitted light beam and applies the recombined light to a detector 33.

If the cable is free of defects, the detector 66 receives the maximum widening signal. However, if the cable is defective, the signal received by detector 66 will be attenuated due to the relative phase shift between the two parts. This attenuation is used to detect the presence of faults within the cable.

[Brief explanation of drawings]

1 is a half-sectional view of a cable according to the invention; FIG. 2 is a longitudinal half-sectional view of the cable of FIG. 1; FIG. 6 is a partial view corresponding to FIG. 2 in the case of moisture; 4 is a block diagram for detecting and finding defects in a cable according to the present invention, FIG. 5 is a graph diagram explaining the operation of the structure of FIG. 4, and FIG. 6 is a modification of FIG. 4. Explanation of reference symbols 1...Conductor 2, 4...Semiconductor layer 3.
...Synthetic insulating sheath 5...Water expansion tape 6...Conducting wire 7...Aluminium no sheath 8...Insulating sheath 9.10...Light guide 20...Laser emitter 22 ...Receiver 31,,32...Semi-transparent mirror 33...Detector patent applicant Thomson-Gemont Cabre

Claims (1)

[Claims] 1. An insulated cable for transmitting electrical power, said cable including at least one optical fiber embedded throughout its length, said optical fiber being sensitive to temperature and/or moisture fluctuations. , and at least one end of the cable can be connected to a device for detecting or measuring the level of temperature and/or humidity or variations thereof. 2. An insulated cable according to claim 1, wherein the optical fiber is disposed between an inner insulating layer and a metal screen. 6. In the cable according to claim 2,
An insulated capeple characterized in that the insulation is surrounded by a semiconductor layer and the optical fiber is disposed between the semiconductor layer and a metal screen. 4. In the cable according to claim 2,
An insulated capeple characterized in that the optical fiber is arranged adjacent to a longitudinally extending conductor serving as part of a screen. 5. In the cable according to claim 1,
The optical cable is placed next to a material that expands when wetted, and the penetration of water into a portion of the cable causes local deformation of the optical fiber, which deformation causes the detection or measurement to take place. Features an insulated cable. 6. In the cable according to claim 5,
An insulating capeple, characterized in that the expansion material is in the shape of a tape. Z. An insulated cable for transmitting electrical power, said cable comprising at least one optical fiber embedded throughout its length, said optical fiber being sensitive to temperature and/or moisture fluctuations, and at least one end of said cable of,
A device for detecting defects in an electrically insulated cable, characterized in that it can be connected to a device for detecting or measuring the level of temperature and/or moisture or variations thereof, the device being capable of emitting light for applying light to an optical fiber embedded in said cable. A defect detection device for a cable, comprising: a light receiver at one end of the cable, and a light receiver for receiving light returned to the one end by back-diffusion within the optical fiber.