JPH11271381A - Method for orienting failure point of power cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further exactly orient a failure point even when the increase of a temperature is small by judging the failure of a power cable under the consideration of elements other than the increase of a temperature. SOLUTION: The distribution of a temperature in the longitudinal direction of a power cable 1 is detected by a distribution type temperature sensor main body 4, and a first judgement reference 1 whether or not the increase of a temperature at a measuring point is a prescribed value or more compared with a normal time, a second judgement reference 2 whether or not a difference between a mean temperature in prescribed length before and after the measuring point and the temperature at the measuring point is the prescribed value or more, and a third judgement reference 3 whether or not the temperature is decreased for each measurement at the prescribed times of measurement at the measuring point is judged at each measuring point in the longitudinal direction of the power cable 1 by a computer 21 based on the detected distribution of a temperature. Thus, the failure point of the power cable can be oriented based on the judged result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for locating a fault point in a power cable, and more particularly to a method for locating a fault point based on a rise in temperature, particularly when a distributed temperature sensor is used. To improve the orientation accuracy of

[0002]

2. Description of the Related Art Conventionally, in a power cable, an insulation breakdown has occurred due to the application of an impact voltage due to a lightning strike, the deterioration of the insulation of the power cable or the damage to the power cable. A ground fault that flows through the power cable may cause damage to the power cable.
The fault location technology for detecting the point of occurrence of a fault such as a ground fault in a power cable involves providing an optical fiber in the power cable and determining the position of the power cable in which the disconnection accident occurred. (For example, JP-A-60-174960 and JP-A-61-964)
No. 77). However, such a technique has a disadvantage that a failure point cannot be located unless an abnormality occurs in the optical fiber.

On the other hand, a distributed temperature sensor is provided on a power cable to measure the temperature distribution in the longitudinal direction of the power cable, and a point where the temperature rises after the occurrence of the failure than before the occurrence of the failure is determined as an accident point. (For example, Japanese Patent Application Laid-Open No. 4-70527)
Reference). That is, in the technology described in this publication, the temperature distribution in the length direction is measured by using a Raman scattering type optical fiber type distribution thermometer and aligning the optical fiber serving as the temperature detection unit along the length direction of the power cable. By measuring, a position (peak position) at which the temperature rises due to an accident such as a ground fault accident on the power cable line is detected, and the accident occurrence point is obtained.

[0004] The principle of measuring the temperature distribution by the Raman scattering type optical fiber type distributed temperature sensor is as follows. That is, when light is incident on the optical fiber, slight fluctuation of the refractive index in the optical fiber, absorption by molecules and atoms constituting the optical fiber, and scattering by re-emission occur.
The scattered light includes Rayleigh scattered light having the same wavelength as the incident light and Raman scattered light having a different wavelength from the incident light. The latter Raman scattered light is scattered light generated by thermal vibration of molecules and atoms constituting the optical fiber, and the intensity thereof largely depends on temperature. Therefore, pulsed light (usually laser light) of a specific wavelength is used as the incident light, and the time delay until the light returns due to the scattered light and the intensity of the Raman backscattered light are detected. The temperature at each position in the length direction can be measured.

[0005]

However, even if the temperature distribution in the longitudinal direction of the power cable is measured by the above-mentioned conventional technique and a position where the temperature rise is high is regarded as a failure point, the conductor temperature of the cable is directly measured. Since it is difficult or impossible to measure the temperature, the temperature of the shield layer of the power cable or the surface of the cable is measured, and when the temperature rise due to a failure is small, it is difficult to accurately locate the position. For example, FIG.
As shown in FIG. 1, even when the optical fiber cable b is arranged along the power cable a, in the case of the power cable a having a small ground fault capacity, even if a ground fault occurs at the point c of the power cable a, The fiber cable b has a problem in that it cannot detect a temperature rise exceeding a predetermined value that can be determined as an accident, and cannot accurately locate a fault point.

On the other hand, if the predetermined temperature for judging an accident is simply lowered, the accident may be judged as an accident even though no accident has occurred due to a rise in temperature during power transmission. Also, it is conceivable that the optical fiber cables b1, b2, b3,... Are densely arranged on the surface of the power cable as shown by a broken line in FIG.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. More specifically, a failure of a power cable is determined by incorporating factors other than temperature rise, and more accurate even when the temperature rise is small. An object of the present invention is to provide a power cable fault point locating method capable of locating a fault point.

[0008]

According to a first aspect of the present invention, there is provided a distributed type temperature sensor arranged along a power cable to be measured, and a temperature distribution in a longitudinal direction of the power cable is measured. In the method of detecting and locating a fault point of a power cable based on a detected temperature distribution, a first determination criterion as to whether a temperature rise at a measurement point is equal to or more than a predetermined value as compared with a steady state, based on the detected temperature distribution, A second criterion for determining whether the temperature difference between the average temperature of the predetermined length before and after the measurement point and the measurement point is equal to or more than a predetermined value, and whether the temperature decreases for each measurement in the predetermined measurement of the measurement point That third criterion,
It has a configuration of a method for locating a fault point of a power cable, characterized by determining each measurement point in the longitudinal direction of the power cable and locating a fault point of the power cable based on a result of the determination.

The inventor disposes an optical fiber in a power cable and detects the temperature distribution of the power cable by the optical fiber, for example, as shown in FIG. Using four composite cables. As a result, the ground fault capacity is small (for example, 200 A ×
At 0.1 seconds), it was found that the temperature measured by the optical fiber at a portion 90 ° in the circumferential direction from the failure point was less than the temperature rise of 5 ° C, which is the accident point determination level.

If a fault point is located using two optical fibers, it is necessary to be able to locate a fault point at a position 90 ° apart in the circumferential direction. Therefore, as a result of studying a method of locating a failure point when the temperature rise is less than 5 ° C., the present invention was made.

According to the first aspect of the present invention, the distribution type temperature sensor detects the temperature distribution in the longitudinal direction of the power cable,
When locating a failure point of a power cable based on a detected temperature distribution, a first criterion for determining whether a temperature rise at a measurement point is equal to or more than a predetermined value as compared with a steady state based on the detected temperature distribution, A second criterion for determining whether the temperature difference between the average temperature of the predetermined length and the measurement point is equal to or more than a predetermined value, and a third determination whether or not the temperature decreases for each measurement in the predetermined measurement of the measurement point. Is determined for each measurement point in the power cable longitudinal direction. Further, based on the result of the determination, the fault point of the power cable is located. Therefore, the failure point is located based on the second and third criteria other than the temperature rise, so that the failure point can be located even when the temperature rise is small due to the failure.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an explanatory view of a fault locating device compatible with multiple lines according to an embodiment of the present invention, FIG. 2 is a detailed configuration diagram of each optical path switch 2b, 3b of the fault locating device, and FIG. It is a detailed explanatory view of 17, 18, and 19.

The fault point locating device shown in FIG. 1 is a temperature distribution measuring optical fiber 2a (2a1-2a) disposed along three power cables 1 (1.1, 1.2, 1.3).
3) First and second fiber detectors 2 and 3 having 3a (3a1 to 3a3), and laser pulse light incident on the first and second fiber detectors 2 and 3 and light for temperature distribution measurement. Fibers 2a (2a1-2a3), 3a (3a1-3a)
3), the sensor main body 4 for detecting the Raman scattered light, the digital averager 20 for averaging the detected Raman scattered light signal, and converting the averaged data to temperature distribution data. A computer 21 for outputting a control command to the point location device.

The first and second fiber detectors 2 and 3 are temperature distribution measuring optical fibers 2a (2a1-2a3), 3a
In addition to (3a1-3a3), a first 1 × N optical path switch 2b for switching each temperature distribution measuring optical fiber 2a (2a1-2a3) and injecting laser pulse light, and the optical path switch 2b as a sensor body 4 And a first connection portion 2c connected to each of the optical fibers 3a (3a1-2).
a1) to switch laser pulse light by switching a3)
It has an xN optical path switch 3b and a second connection part 3c for connecting the optical path switch 3b to the sensor body 4.

The configuration of the optical path switches 2b and 3b of the first and second fiber detectors 2 and 3 is shown in FIG.
As shown in FIG. 2B, the light emitting device includes reflecting mirrors 33 and 34 for reflecting light from the connecting portions 2c and 3c, and a motor 30 for rotating the reflecting mirrors 33 and 34 via rotation shafts 31 and 32. I have. The incident side ends of the optical fibers 2a, 3a are arranged along a circumference centering on the reflecting mirrors 33, 34, and the connection parts 2c,
The light from 3c is switched so as to be incident on the incident end of each of the optical fibers 2a, 3a.

Note that, as shown in FIG.
An overcurrent sensor for detecting that an overcurrent has occurred in 1, 1, 2, and 1 is provided, and an overcurrent sensor signal is input to the overcurrent signal processing device 22. ing. The overcurrent signal processing device 22 outputs a contact relay signal to the computer 21.

Here, the laser pulse light emitted from the light source 5 of the sensor main body 4 is incident on an optical splitter 6, which splits the incident light into two directions. One of these two split lights (laser pulse light) is incident on the first fiber detection unit 2 via the first splitter 7. Further, the branched light is incident on the optical fibers 2a1-2a3 from the first fiber detection unit 2, and the optical fibers 2a1-2a.
The backward Raman scattered light is emitted from 3, and the backward Raman scattered light enters the first splitter 7 via the first fiber detector 2.

The first demultiplexer 7 demultiplexes the backward Raman scattered light into a first Stokes light (1) and a first anti-Stokes light (1 '). Incident. The light receiving elements 9 and 10 convert the first Stokes light (1) and the first anti-Stokes light (1 ′) into Stokes electric signals and anti-Stokes electric signals, respectively, and output the signals to the amplifiers 13 and 14, respectively. Each of the amplifiers 13 and 14 amplifies the Stokes electric signal and the anti-Stokes electric signal and guides the amplified electric signal to the first electric switch 17.

On the other hand, the other of the two branched lights (laser pulse light) enters the second fiber detector 3 via the second splitter 8. In addition, the split light is the second light.
The optical fiber 3a1-3a3 is incident on the optical fibers 3a1-3a3 from the fiber detection unit 3, and the backward Raman scattered light is emitted from the optical fibers 3a1-3a3. It is incident on the wave device 8. The second demultiplexer 8 demultiplexes the backward Raman scattered light into a second Stokes light (2) and a second anti-Stokes light (2 ′), and makes them enter the light receiving elements 11 and 12, respectively.

The light receiving elements 11 and 12 respectively provide a second Stokes light (2) and a second anti-Stokes light (2 ').
Is converted into a Stokes electric signal and an anti-Stokes electric signal and output to the amplifiers 15 and 16. Amplifier 15 amplifies the Stokes electrical signal and directs it to a second electrical switch 18. Amplifier 16 amplifies the anti-Stokes electrical signal and directs it to a third electrical switch 19.

The first electric switch 17 has two input terminals 17a, 17a and two output terminals 17b, 17b. These two input terminals 17a, 17a are connected to amplifiers 13, 14, respectively. The two output terminals 17b, 17b are connected to a second electric switch 18 and a third electric switch 19, respectively. The second electric switch 18 has two input terminals 18a, 18a.
a and one output terminal 18b. One of the two input terminals 18a, 18a is connected to the output terminal 17b of the first electric switch 17, and the other is connected to the amplifier 15. The third electric switch 19 has two input terminals 19a, 19a and one output terminal 19b. One of the two input terminals 19a, 19a is connected to the output terminal 17b of the first electric switch 17, and the other is connected to the amplifier 16.

Outputs from the second electric switch 18 and the third electric switch 19 are input to the digital averager 20 as an output signal from the sensor body 4, and an averaging process is performed to reduce noise. Data is transferred from the digital averager 20 to the computer 21,
The computer 21 converts the data into temperature distribution data. The digital averager 20 is, for example, a general-purpose two-channel type. Also, digital averager 2
“0” sends a trigger signal to the light source 5.

By the way, each of the electric switches 17, 18, 1
Numeral 9 is controlled by an electric switch control signal from the computer 21, and is configured to switch to the first, second and third systems as shown in FIGS. 3 (a), 3 (b) and 3 (c). I have. The first and second systems are used for normal temperature measurement, and the third system is used when a cable fails.

As shown in FIG. 3A, the first system includes a Stokes light (1) output from the first fiber detection unit 2.
From the first electric switch 17 to the second electric switch 1
8 to the digital averager 20. At the same time, the anti-Stokes light (1 ′) output from the first fiber detection unit 2 is input from the first electric switch 17 to the digital averager 20 via the third electric switch 19. Further, as shown in (b), the second system inputs the Stokes light (2) output from the second fiber detection unit 3 to the digital averager 20 via the second electric switch 18. At the same time, the anti-Stokes light (2 ′) output from the second fiber detector 3 is input to the digital averager 20 via the third electric switch 19. Also,
As shown in (c), the third system converts the anti-Stokes light (1 ′) output from the first fiber detector 2 from the first electric switch 17 to the digital average through the second electric switch 18. Input to the keyer 20. At the same time, the anti-Stokes light (2 ′) output from the second fiber detector 3 is input to the digital averager 20 via the third electric switch 19.

FIG. 4 is a basic flowchart of the fault locating apparatus according to the present embodiment. As shown in FIG. 4, first, at all times, the power cables 1, 1, 1, 2, 1.
The temperature distribution in step 3 is measured to determine whether an accident has occurred (step 1). If it is determined that an accident has occurred, the measurement is instantaneously switched from the continuous measurement to the temperature measurement in the accident occurrence phase. It is determined whether or not the optical fiber cable is disconnected (step 2). If there is a disconnected part, it is regarded as a disconnected part due to an accident, and a fault point is located (step 5). . If there is a place where the temperature has risen by 5 ° or more than the steady state even when there is no core break (step 3), the fault point is located (step 5). If the optical fiber cable is not disconnected and there is no place where the temperature rises by 5 ° C. or more, a failure is determined according to the present invention when the temperature rise is less than 5 ° C. (step 4). If a failure is determined, a failure point is located (step 5).

Steps 1 to 5 will be described in detail.
The normal temperature measurement procedure in step 1 will be described. The first temperature distribution measuring optical fiber 2a and the second temperature distribution measuring optical fiber 3a disposed on the power cable 1 are optically connected (optical connector connection, optical fusion connection). A switching control signal is sent from the computer 21 to the first fiber detection unit 2 and the second fiber detection unit 3. By this signal, the first 1 × N optical path switch 2b and the second 1 × N optical path switch 2b
xN optical path switch 3b is connected to first power cable 1.1
Is optically connected to the temperature distribution measuring optical fibers 2a1 and 3a1. The computer 21 includes the electric switch 1
The electric switch control signal is sent to 7, 18, and 19. This signal causes the electric switches 17, 1 and 1 to operate as in the first system.
8 and 19 are controlled. As a result, the temperature distribution of the temperature distribution measuring optical fiber 2a1 of the first power cable 1.1 is measured.

Next, an electric switch control signal is transmitted from the computer 21 to the electric switches 17, 18, and 19. The electric switches 17, 18, and 19 are controlled by this signal as in the second system. As a result, the temperature distribution measuring optical fiber 3a1 of the first power cable 1.1
Is measured.

Next, a switching control signal is transmitted from the computer 21 to the first fiber detection unit 2 and the second fiber detection unit 3. By this signal, the first 1 × N optical path switch 2b and the second 1 × N optical path switch 3b
Is optically connected to the temperature distribution measuring optical fibers 2a2 and 3a2 of the second power cables 1 and 2. The computer 21 sends out electric switch 17, 18, and 19 electric switch control signals. With this control signal, the electric switches 17, 18, and 19 are controlled as in the first system. As a result, the temperature distribution of the temperature distribution measuring optical fiber 3a2 of the second power cables 1 and 2 is measured.

Next, an electrical switch signal is sent from the computer 21 to the electrical switches 17, 18, and 19.
The electric switches 17, 18, and 19 are controlled by this signal as in the second system. As a result, the temperature distribution of the temperature distribution measuring optical fiber 3a1 of the second power cables 1 and 2 is measured.

Thereafter, by the same procedure as described above, the temperature distribution measuring optical fibers 2a3,
The temperature distribution of 3a3 is measured.

Here, the procedure for measuring the temperature at the time of cable failure in steps 1 to 3 is as follows. In step 1, the occurrence of an accident is detected by, for example, an overcurrent sensor. That is, the overcurrent signal processor 22 monitors the occurrence of an overcurrent in at least one of the power cables 1, 1, 1, 2, and 1 by a signal from the overcurrent sensor provided in the power cable 1. ing. When an overcurrent occurs, a contact relay signal is sent from the overcurrent signal processing device 22 to the computer 21. The computer 21 recognizes the failed power cable 1 based on the signal.

Description will be made on the assumption that the third power cables 1 and 3 are out of order. A switching control signal is sent from the computer 21 to the first fiber detection unit 2 and the second fiber detection unit 3. With this signal, the first 1x
N optical path switch 2b and second 1 × N optical path switch 3
b measures the temperature distribution of the temperature distribution measuring optical fibers 2a3 and 3a3 of the third power cable. Based on the temperature measurement result, a cable fault point is located.

Further, the failure detection in step 4 when the temperature rise is less than 5 ° C. is as follows. If there is a temperature rise due to a failure, there should be the following features in that point. [1] The temperature is higher than in a steady state. [2] The temperature is higher in the longitudinal direction than before and after. [3] The temperature drops every measurement 1 → 2 → 3 times after the occurrence of the failure.

At each point of the optical fiber, for each of these three conditions [1] to [3], a function f _i () indicating the possibility that the point of the optical fiber length x (m) is a failure point is high. x) (0 ≦ f _i (x) ≦ 1) (1) is introduced, and P (x) = w ₁ f ₁ (x) + w ₂ f ₂ (x) + w ₃ f ₃ (x) (2) Where w ₁ , w ₂ , w ₃ : conditions [1], [2], [3]
It is determined that the possibility of a failure point is higher in the order of the weight with respect to.

[1] Temperature rise from steady state. The temperature of the optical fiber at m (m) in a steady state (before the failure) is t (m, 0), and the temperature measurement result at the n-th time after the failure is t (m,
As n), f ₁ (x) is determined as in the following equation and FIG.

(Equation 1)

[2] Comparison with average before and after. For example, by the temperature difference between the average of 3 m before and after and the point, f
₂ Determine (m). Here, it is assumed that if there is a temperature difference of 5 ° C. or more, there is a high possibility of a failure point.

(Equation 2)

[3] The temperature decreases every measurement, ie, 1 → 2 → 3 times. This condition is either true or false.
It becomes street.

(Equation 3)

(Determination of Failure) In order to confirm the effect of the present invention, the present inventor applied to four samples (TNos. We examined whether the method could determine the failure point. The sample in this case is a 77 k VCV cable 1 × 40
At 0 mm ² (copper tape shielding), four optical fibers θ1 to θ4 are compounded around the power cable 1 so as to be equally distributed in the circumferential direction as shown in FIG. The lengths of the optical fibers θ1 to θ4 provided on the power cable are approximately 6 to 7 (m), respectively, and a wire is driven into the power cable at a substantially central position in the longitudinal direction to generate a ground fault. This was tested. Further, the optical fibers θ1 to θ4
Is connected to the series, and the optical fibers θ1 to θ4
The temperature distribution is measured for the total extension of. Optical fibers θ1 and θ2 are optically coupled at one end, and optical fibers θ2 and θ3
Are optically coupled at the other end, θ3 and θ4 are optically coupled at one end, and laser pulse light is incident from the end of the optical fiber θ1 to measure the temperature distribution.

Table 1 and FIGS. 7 to 9 show the results of temperature measurement during the ground fault test for the four examples examined. 7 to 9, the temperature distribution of the optical fiber θ4 broken by the ground fault of the power cable is omitted. As a result of the test, the optical fiber was broken at θ4 in all samples (TNo. 815, 817, 818, and 819), and the temperature rise of θ1 to θ3 was 5 ° C.
Is less than. This time, three conditions [1] to [3]
Weight w ₁ to w ₃ for was a _{w 1 = 0.4 w 2 = 0.4} w 3 = 0.2.

[0040]

[Table 1]

(Discrimination Results) The discrimination results are shown in Tables 2 to 5.
The shaded portions in the table indicate the positions of the optical fibers θ1 to θ3 corresponding to the positions near the ground fault portion. The table on the right shows P
(M). From this result, 4
In both samples, P (m) is the largest at θ1 or θ3, which indicates that the method of the present invention is useful as a method for determining a failure point.

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

[Table 4]

[0045]

[Table 5]

In the above-described embodiment, the device for locating the fault point with respect to a plurality of power cables has been described. However, the scope of the present invention can be implemented with a single power cable. The numerical values of the (3) to (5) and the weights w ₁ to w ₃ functions f _i that indicates the possibility of height of fault point is an example of the present invention, appropriate other formulas or numeric Can be used.

[0047]

As described above, according to the present invention, it is possible to determine the fault of the power cable by taking in factors other than the temperature rise, and to more accurately locate the fault point even when the temperature rise is small.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an overall configuration of a fault point locating device according to an embodiment of the present invention.

FIG. 2 is a detailed configuration diagram of each optical path switch of the fault point locating device of FIG. 1;

FIG. 3 is a detailed explanatory diagram of each electric switch of FIG. 1;

FIG. 4 is a basic flowchart of a failure point evaluation method according to the embodiment.

FIG. 5 shows a graph that defines one of the functions f ₁ (m) indicating the possibility of being a failure point in the embodiment.

FIG. 6 is an explanatory diagram of a cable and an optical fiber installation of a sample for locating a fault according to the present invention.

FIG. 7 is a graph showing an example of a result obtained by performing the fault locating according to the present invention on one sample.

FIG. 8 is a graph showing an example of a result obtained by performing the fault locating according to the present invention on another sample.

FIG. 9 is a graph showing an example of a result obtained by performing the failure point localization according to the present invention on another sample.

FIG. 10 is a graph showing an example of a result obtained by performing the fault locating according to the present invention on another sample.

FIG. 11 is an explanatory diagram of arranging optical fibers in a general power cable.

[Explanation of symbols]

1 (1.1, 1.2, 1.3) Power cable 2, 3 First and second fiber detector 2a (2a1-2a3), 3a (3a1-3a3) Optical fiber for temperature distribution measurement 2b, 3b 1st, 2nd 1xN optical path switch 2c, 3c 1st, 2nd connection part 4 Sensor main body 5 Light source 6 Optical splitter 7,8 First, 2nd demultiplexer 9,10,11,12 Light reception Element 20 Digital averager 21 Computer 22 Overcurrent signal processing device

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Chino 2-6-1 Nagasaka, Yokosuka City, Kanagawa Prefecture, Central Research Institute of Electric Power Industry

Claims (1)

[Claims] 1. A method for detecting a temperature distribution in a longitudinal direction of a power cable by a distributed temperature sensor disposed along a power cable to be measured, and locating a fault point of the power cable based on the detected temperature distribution. A first criterion for determining whether the temperature rise of the measurement point is equal to or more than a predetermined value as compared with the steady state, based on the detected temperature distribution, and the temperature difference between the average temperature of the predetermined length before and after the measurement point and the measurement point; The second criterion for determining whether or not the temperature is equal to or more than a predetermined value and the third criterion for determining whether the temperature decreases at each measurement in the predetermined measurement of the measurement point are determined for each measurement point in the longitudinal direction of the power cable. A method for locating a fault point of a power cable, comprising: determining a fault point of the power cable based on a result of the determination.