JPH0735809A - Method and aparatus for detecting fault point of power cable - Google Patents

Abstract

PURPOSE:To eliminate erroneous detection by factors other than faults by extracting a point with a variation of temperature larger than a specified value as a fault candidate point to detect a fault point based on the change with time in the temperature at the candidate point and the temperature distribution in front and in rear of the candidate point. CONSTITUTION:When a fault is generated, a trip signal is detected with a trigger signal generator 4. The trigger signal is inputted to a temperature distribution measuring device 3 to start the location of a fault point. The measuring device 3 measures a temperature distribution along the length of an optical fiber 2 based on a detection light from the optical fiber 2 along a pipeline or the like where a power cable 1 is installed. The temperature distribution measured is inputted into a fault location device 5 and when a variation of the temperature exceeds a specified value at a point, the point is extracted as fault candidate point. As the rise in the temperature as caused in case of a ground fault is faster in the rising as compared with the temperature rise by other factors, faster rise in the temperature at the candidate point indicates that the candidate point is the fault point. When a temperature rise occurs in a narrow range before and after the candidate point, the candidate point is identified as a fault point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for measuring a temperature distribution in a longitudinal direction of a power cable and detecting a failure point of the power cable based on the measurement, and more particularly to a method and a device other than the failure. The present invention relates to a power cable fault point detection method and apparatus for eliminating false detection.

[0002]

2. Description of the Related Art In a power cable, when a shock voltage due to a lightning strike is applied, the insulator forming the power cable is deteriorated, or the power cable is damaged by damage, the damaged portion is damaged. There is a case where a so-called ground fault (fault) occurs in which a large current flows in the grounding system due to dielectric breakdown, and the power cable is severely damaged. For example, as shown in FIG. 6, an underground cable 6 for transmitting power
Although No. 1 is laid in the cave 62, a large current may flow to the ground system due to a ground fault and may cause a serious damage.

At the electric station 63, the occurrence of a failure is detected by monitoring the system current, and when the failure occurs, the relay and the like are automatically shut off. In addition, the location of the failure is also detected. This is called fault location. The Murray loop method and the pulse radar method are used for locating the failure point. The Murray loop method is based on the principle of the bridge, and measures the resistance up to the failure point by using the core of the failed cable as one side of the bridge. The pulse radar method captures the reflection of electrical pulses from a fault point.

In recent years, a large number of optical fibers are arranged in or on the surface of a power cable, and the broken position of the optical fiber broken by arc energy generated at the time of ground fault is measured by the OTDR method, and the failure point is located from this broken point. How to do it is considered.

Further, an optical fiber is laid along the power cable, the temperature distribution in the longitudinal direction of the optical fiber is measured using a temperature distribution measuring device, and the temperature rise caused by a ground fault from the change in the temperature distribution. There has been considered a method of detecting a fault and locating a failure point.

[0006]

In the Murray loop method and the pulse radar method, a measuring device cannot be installed until it is known that a failure has occurred. Therefore, it takes time to locate the failure point after the failure occurs. . Further, the location accuracy of the fault location is poor, and it is necessary to conduct a patrol inspection after the location to identify the fault point. Therefore, failure recovery will be slower if these methods are used.

In the method of detecting the disconnection position of the optical fiber by the OTDR method, when the ground fault energy is small, the optical fiber may not be disconnected and the orientation may not be possible. Also,
When the direction in which the ground fault occurs is the direction in which the optical fiber is not arranged, the influence of the ground fault energy received by the optical fiber is small. In this case as well, the optical fiber is not broken, and orientation cannot be performed. It is necessary to arrange as many optical fibers as possible inside the power cable in order to perform fault location without being affected by the ground fault direction or the ground fault energy, but this is difficult in practice.

The method of locating a fault point from the temperature distribution in the longitudinal direction is superior to the above method, but it is accompanied by a temperature rise caused by a ground fault and other temperature fluctuations, such as a change in the temperature in a cave. It is difficult to distinguish it from the temperature change and the like due to the operation of the ventilation fan, and if it becomes worse, the wrong place may be located as the failure point.

Therefore, an object of the present invention is to solve the above problems and provide a power cable fault point detection method and apparatus for eliminating erroneous detection due to factors other than a fault.

[0010]

In order to achieve the above object, the present invention provides an optical fiber along an electric power cable or a cavern, a duct or the like in which the electric power cable is installed. In the power cable failure point detection method, in which light is incident from one end of the cable, the temperature distribution in the longitudinal direction of the optical fiber is measured from the backscattered light distribution, and the failure point of the power cable is detected from the temperature distribution. Is extracted as a failure candidate point that is larger than a predetermined amount, and the failure point is detected based on the temporal change in temperature at the candidate point and the temperature distribution before and after the candidate point.

In order to extract the failure candidate point, first, a trip signal of the power cable is received, the temperature distribution is measured immediately after the trip signal is received, and the change amount of the temperature distribution before and after the trip signal is received is obtained. You may do it.

The power cable fault point detecting device is composed of an optical fiber along an electric power cable or a cavern, a conduit, etc. in which the electric power cable is laid, and a backscattered light distribution of light incident from one end of the optical fiber. In the power cable fault point detecting device having a temperature distribution measuring device for measuring the temperature distribution in the longitudinal direction of the optical fiber, the extracting means for extracting the fault candidate points in the descending order of the temperature change amount, and the extracted candidate points. Detects whether or not the candidate point is a failure point by comparing the temporal change in temperature with preset temporal data and comparing the temperature distribution before and after the candidate point with preset distribution data. And a failure point detecting means for performing the operation.

[0013]

With the above structure, the temperature distribution in the longitudinal direction of the optical fiber can be detected. If the temperature distribution changes, the amount of change in temperature along the optical fiber can be known. When the amount of change in temperature at a certain point is larger than a predetermined amount, there is a possibility that a failure has occurred at that point, so this is extracted as a failure candidate point. At a candidate point, the temporal change in temperature at that point and the temperature distribution before and after the candidate point are examined. Since the rise in temperature caused by a ground fault rises faster than the rise in temperature due to other factors, if the rise in temperature at a candidate point is fast, it can be determined that this candidate point is a failure point. In addition, the temperature rise that occurs during a ground fault occurs more locally than the temperature rise due to other factors, so if the temperature rise appears in a narrow range before and after the candidate point, it is determined that this candidate point is a failure point. You can Reliable orientation can be obtained by using each orientation result in combination. For example, candidate points are narrowed down to one point by orientation based on temperature change, and confirmation is performed by orientation based on temperature distribution.

By receiving the trip signal generated in the power cable at the time of the ground fault, it can be known that the ground fault has occurred somewhere in the power cable when the trip signal is received. If the temperature distribution is measured from this point in time, the temperature change before and after the ground fault can be captured, so that the candidate points can be extracted and the fault points can be located quickly and accurately.

Further, the extraction of the candidate points may be performed in descending order of the amount of change. In order to locate the failure point from the temporal change of the temperature at the candidate point, the temperature change or its characteristic amount caused by the ground fault is set in advance as the time data, and the measured value and the time data are compared. Good. In order to locate the failure point from the temperature distribution before and after the candidate point, it is preferable to set the temperature distribution generated by the ground fault or its characteristic amount in advance as distribution data and compare the measured value with the distribution data. Reliable orientation can be obtained by using each orientation result in combination. For example, only when the orientation based on the temperature change and the orientation based on the temperature distribution match, the candidate point is set as the failure point.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, the power cable fault point detection system is installed mainly along the power cable 1 and cable installation equipment such as a cave and a pipeline to detect the temperature distribution. An optical fiber 2 that transmits light, a temperature distribution measuring device 3 that measures the temperature distribution in the longitudinal direction based on the detection light from the optical fiber 2, and a power cable 1 when a ground fault occurs.
It comprises a trigger signal generator 4 for detecting a trip signal flowing through and generating a trigger signal for locating start, and a fault point locating device 5 for locating a fault point based on the measured temperature distribution.

In the present embodiment, the power cable has three conductors and is supplied with three-phase power from the power supply section. The optical fiber 2 and the temperature distribution measuring device 3 may be known ones. The trigger signal generator 4 is configured as a receiving unit that receives the trip signal of the power cable 1 from the CT (current conversion coil) 6 attached to the conductor of each phase. Also, a trigger signal can be generated to reset the temperature distribution measuring device 3 and restart the measurement.

A specific operation of this system will be described.

The operation of this system is roughly divided into two. First, the first is the operation before the failure occurs, and the second is the operation after the failure occurs.

In the first operation before the failure occurs, the system can monitor the operating status of the power cable equipment. That is, by measuring the temperature of the surface of the power cable and the temperature of various power facilities, it is possible to monitor the abnormal temperature during the operation of the transmission line, and to constantly monitor the fire in the cave. Specifically, the temperature distribution measuring device 3 measures the temperature distribution of the transmission line, and the measured temperature data of each point of the line is transferred to the fault point locating device 5. The fault point locator 5 sets an abnormal temperature at each point in advance, and points beyond this are set as abnormal points and an alarm is issued. In order to detect an abnormality quickly, it is desirable that the measurement time of the temperature distribution measuring device 3 be as short as possible. In the case of this system, the measurement time was set to several tens of seconds. In addition, the failure point locator 5 obtains an average temperature value at each point based on the temperature data sent, and compares the average temperature value with one measurement value to detect an abnormal temperature. To do. The reason why the average temperature value is used is to reduce the influence of the measurement error of the measured temperature value and accurately detect the abnormal temperature. In this system, the averaging time width was set to several tens of minutes in order to make it considerably smaller than the daily fluctuation time of the power equipment temperature.

In the second operation when a failure occurs, the trip signal is detected by the trigger signal generator 4.
In this case, as the trigger signal generator 4, it is preferable to use the CT 6 which can be configured by simple parts. Now, the trigger signal generator 4 inputs the trigger signal to the temperature distribution measuring device 3, and the fault point localization is started from this. The temperature distribution measuring device 3 immediately resets the temperature distribution measurement data during the measurement up to that point and restarts the measurement by the trigger signal. Since the ground fault occurrence time and the measurement start time of the temperature distribution measuring device 3 are the same, the temperature rise at the time of the ground fault can be measured more accurately and efficiently.

Next, the operation of the fault point locating device 5 will be described.

After receiving the trigger signal, the fault point locating device 5 first checks (1) whether or not the optical fiber is broken, and (2) extracts a ground fault candidate point, and (3) The ground fault point is located from the candidate points based on the rise time of the temperature rise and (4) the spread of the temperature rise near the candidate point. When it cannot be located by this, the candidate points are re-extracted and the ground fault points are located by the same processing as in (3) and (4).

Each item will be described below.

(1) Detection of Break Point of Optical Fiber When the optical fiber 2 is broken, the temperature distribution measuring device 3 has a large temperature change at points after the break point as shown in FIG. 3 (a). The measurement result is as follows. In order to detect this variation, a temperature difference is set in advance (Ta is set: several tens to several hundreds of degrees). That is, the temperature difference (difference between the past average temperature and the current temperature) at each point on the optical fiber 2 before and after the generation of the trip signal is obtained, and when the absolute value of this temperature difference exceeds the set value Ta, Optical fiber 2
Is determined to be broken, and the near end on the temperature distribution measuring device 3 side is located as a ground fault point.

(2) Extraction of Candidate Point When the optical fiber 2 is not broken, a candidate point as a ground fault point is extracted as shown in FIG. 3 (b). For this, the temperature rise value that occurs at the time of a ground fault is set in advance (Tb: several tens of degrees as an example). A point where the difference between the average temperature distribution before the trip signal is generated and the temperature difference after the trip signal obtained in (1) exceeds the set temperature value Tb is picked up as a candidate point.
Here, the set temperature value Tb is initially set to several tens of degrees in order to distinguish it from the temperature increase due to various factors other than the ground fault. If there is no point that exceeds this setting, the set value is gradually lowered and this is repeated until a candidate point is extracted.
If no candidate point is found at the end, then the candidate point is absent.

(3) Evaluation of Temporal Characteristics of Temperature of Candidate Point The temperature change of the candidate point with time is obtained, and the rise time thereof is obtained. As shown in FIG. 3C, the rise time of the temperature rise due to the ground fault is the temperature rise due to other factors (temperature change in the cavern, temperature fluctuation due to ventilation fan operation, etc.).
Since it is shorter than that of, the candidate points are narrowed down using this as a criterion.

(4) Evaluation of spread of temperature rise near the candidate point (referred to as distance characteristic) The narrowed candidate point is evaluated for spread of temperature rise near the candidate point and confirmed as a ground fault point. Figure 3 (d)
As shown in (3), the spread of the temperature rise at the ground fault is used as compared with that due to other factors.

Next, another embodiment of the present invention will be described.

As shown in FIG. 2, the failure point detection device 20
Is the same optical fiber 2 and temperature distribution measuring device 3 as in FIG.
The temperature holding circuit 21 holds the temperature distribution information measured by the temperature distribution measuring device 3, the difference in the held temperature distribution information at a predetermined time is obtained, and the temperature difference at the point where the difference appears. Difference detection circuit 22 that detects the position information and the position information, a rearrangement circuit 23 that rearranges the position information in order of increasing temperature difference, a ground fault condition check circuit 24 that checks the ground fault condition, and an orientation result display device that displays the orientation result. Two
It consists of 5.

The temperature holding circuit 21, the temperature difference detection circuit 22, and the rearrangement circuit 23 are the extraction means 7 for extracting the failure candidate points in the descending order of the temperature change amount. The ground fault condition check circuit 24 compares the temporal change of the temperature at the extracted candidate point with preset time-dependent data, and compares the temperature distribution before and after the candidate point with preset distribution data. The failure point detection means 8 detects whether or not the candidate point is a failure point.

In FIG. 2, the temperature distribution data at the point where the optical fiber 2 is divided by 1 m is inputted every 1 minute.
The temperature holding circuit 21 holds these data in order to detect the temperature change at each point. The temperature difference detection circuit 22 calculates the amount of temperature change at each point for each minute. Since the point with a large temperature difference is likely to be a failure point, the rearrangement circuit 2
In 3, the position information is rearranged in the order of increasing temperature difference. As described above, the number of candidate points is not limited to one, and therefore the order in which the orientation is performed must be determined, but it is preferable to perform the order in which the amount of change is large.

In the ground fault condition check circuit 24, the temperature distribution before and after the candidate point is compared with preset distribution data in the order arranged by the rearrangement circuit 23. That is, it is checked whether the spread of the temperature rise has the characteristic at the time of the ground fault. If there is a characteristic at the time of a ground fault, the temporal change of the temperature at the candidate point is compared with preset time-dependent data. That is, the data of the candidate points are arranged in time order from the temperature distribution information held by the temperature holding circuit 21. Then, it is checked whether the state of the temperature change has the characteristic at the time of the ground fault. When both the characteristics of the temperature distribution and the characteristics of the temporal change have the characteristics at the time of the ground fault, the orientation result display device 25 displays the orientation result of the failure point.

In the above embodiment, the fault point is always located, but the fault point may be located after the occurrence of the ground fault is detected by the trip signal. Further, in the rearrangement circuit 23, the points may not be rearranged over the entire length of the cable, but the necessary number may be rearranged from the one having the largest temperature difference.

Next, another embodiment will be described.

In the energy generated at the time of the ground fault, not only the heat generated by the arc energy of the ground fault, that is, the temperature rise, but also some tension (for example, the expansion of the cable connection portion) is applied to the optical fiber laid on the power cable. is there. It is conceivable that the tension causes microbending in the optical fiber, resulting in a change in the transmission loss of the optical fiber at the place where the ground fault occurs.

As a result, the transmission loss changes after the microbend occurs. Looking at the transmission loss measurement result shown in FIG. 4, both of the scattered lights A and S for determining the temperature change. When this is converted into temperature, the temperature at the point after the ground fault point changes as compared with that up to the ground fault point as shown in FIG. As shown in FIG. 5, the temperature may be low or may be high. Therefore, in the orientation procedure, there are a method of using the absolute value of the temperature value as a reference when checking the disconnection of the optical fiber, and a method of checking the transmission loss of the optical fiber every time. This method is effective for detection under the ground fault condition where the temperature rise value is small.

[0039]

The present invention exhibits the following excellent effects.

(1) Temperature fluctuations other than the ground fault are distinguished from the temperature fluctuations of the ground fault, and only the ground fault points are accurately located.

(2) Since the fault point can be located accurately and instantaneously, the fault can be quickly recovered.

[Brief description of drawings]

FIG. 1 is a block diagram of a power cable fault point detection system showing an embodiment of the present invention.

FIG. 2 is a block diagram of a fault point detection device showing another embodiment of the present invention.

FIG. 3 is a graph for explaining the operation of the fault point locating device.

FIG. 4 is a graph showing a change in transmission loss due to generation of a microbend.

FIG. 5 is a graph showing measurement results of temperature distribution when microbends occur.

FIG. 6 is an explanatory diagram of a power cable.

[Explanation of symbols]

 1 Power Cable 2 Optical Fiber 3 Temperature Distribution Measuring Device 4 Trigger Signal Generator 5 Fault Point Locating Device 7 Extracting Means 8 Fault Point Detecting Means

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shunichi Iida 1-3-3 Uchisaiwaicho, Chiyoda-ku, Tokyo Within Tokyo Electric Power Company (72) Mannobu Yokoyama 1-3-1 Uchisaiwaicho, Chiyoda-ku, Tokyo Inside the Tokyo Electric Power Company (72) Inventor Yasuhiro Miyata 5-1-1 Hidaka-cho, Hitachi City, Ibaraki Prefecture Hitachi Cable Co., Ltd. Optro System Research Laboratory (72) Inventor Yoshio Ichi 5 Hidaka-cho, Hitachi City, Ibaraki Prefecture 1-1-1 Hitachi Cable Co., Ltd. Optro System Research Center

Claims (3)

[Claims] 1. An optical fiber is laid along a power cable or a cavern, a duct or the like in which the power cable is laid, and light is made incident from one end of the optical fiber and distributed from its backscattered light distribution. In the power cable fault point detection method of measuring the temperature distribution in the longitudinal direction of the fiber and detecting the fault point of the power cable from the temperature distribution, a point where the amount of change in temperature is larger than a predetermined amount is extracted as a fault candidate point, and A method for detecting a fault point in a power cable, which detects a fault point based on a temporal change in temperature at the candidate point and a temperature distribution before and after the candidate point. 2. In order to extract the failure candidate point, first, a trip signal of the power cable is received, the temperature distribution is measured immediately after the trip signal is received, and the change amount of the temperature distribution before and after the trip signal is received. The power cable fault point detection method according to claim 1, wherein 3. An optical fiber along a power cable or a cavern, pipe or the like in which the power cable is laid,
In a power cable fault point detection device having a temperature distribution measuring device for measuring the temperature distribution in the longitudinal direction of the optical fiber from the backscattered light distribution of the light incident from one end of this optical fiber, a failure candidate in descending order of temperature variation The extraction means for extracting the points and the temporal change of the temperature at the extracted candidate points are compared with preset time data, and the temperature distribution before and after the candidate points is compared with preset distribution data. And a fault point detecting means for detecting whether or not the candidate point is a fault point.