JPH04351973A - Detection method for failure point in underground electric wire - Google Patents

Abstract

PURPOSE:To enable determination of a failure point in a underground electric wire involving connection parts of cables in a short time and with high accuracy. CONSTITUTION:An optical fiber 1 is put inside a plastic pipe 8 installed in a tunnel 10 of an electric power cable 3, and a temperature distribution measuring apparatus 2 for measuring a longitudinal temperature distribution inside the tunnel 10 according to backward scattering light distribution in the optical fiber 1 is provided. A trigger signal is sent to a temperature distribution measuring apparatus 2 at the moment when a trip signal of a underground electric wire is received, the longitudinal temperature distribution of optical fiber 1 is directly measured. Differential values of the temperature distributions' been before and after the trip signal is received are obtained by a data Processor 7, and a position with the maximum differential value is detected as a failure point.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is directed to the failure point of an underground power transmission line,
In particular, the present invention relates to a fault point detection method that is effective for detecting ground fault points.

0002

[Prior Art] Conventionally, dielectric breakdown occurs in power cables due to the application of shock voltage due to lightning strikes, deterioration of the insulation that constitutes the power cable, or damage to the cable due to external trauma, and a large current flows into the grounding system at this point. So-called ground fault accidents, in which cables are severely damaged, are occurring. When such a ground fault occurs, electrical stations have systems in place to determine the fault by monitoring system current and automatically shut off relays and the like. In addition, the fault point can be located using the Murray loop method, which uses the bridge principle and measures the resistance up to the fault point with the core wire of the faulty cable as one side of the bridge, or the pulse pulse method, which captures the reflection of electrical pulses. Radar method is used.

[0003]More recently, many optical fibers have been laid inside or on the cable surface, and OTDR has been developed to detect the location of optical fiber breakage due to arc energy generated during a ground fault.
(Optical Time Domain Ref.
A method of locating the ground fault point from this rupture point has been considered.

0004

However, the prior art described above has the following drawbacks.

(1) In the Murray loop method and pulse radar method, it is necessary to know that a ground fault has occurred.
Because measuring equipment cannot be installed, it takes time to locate the ground after a ground fault occurs. Furthermore, the location accuracy of the accident point is poor, resulting in the need for patrol inspections, and the efficiency of accident recovery is poor.

(2) In the method of detecting the position of an optical fiber break using the OTDR method, the optical fiber may not break because the ground fault energy is small, and location may not be possible. Furthermore, if the optical fiber is not laid in the direction of the ground fault of the cable, the influence of the ground fault energy is small and the wire will not break, making it impossible to locate the cable. Therefore, in order to locate a position that is not affected by the ground fault direction or ground fault energy, it is necessary to arrange as many optical fibers inside the power cable as possible, which is difficult in practice.

An object of the present invention is to eliminate the drawbacks of the prior art described above and provide a ground fault point detection method that can locate the ground fault point of a power cable, including the cable connection, with high precision and in a short time. There is a particular thing.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention lays an optical fiber in a tunnel or conduit where a power cable is installed, and uses the backscattered light distribution of the optical fiber to determine the inside of the tunnel. Alternatively, in an underground power transmission line failure point detection method that measures the longitudinal temperature distribution in the conduit and detects the failure point from that temperature distribution, after receiving a trip signal of the underground power transmission line, this is immediately used as a trigger signal. The temperature distribution in the longitudinal direction of the optical fiber is measured, the difference value between the temperature distributions before and after receiving the trip signal is determined, and the failure point is detected from the position where this difference value is maximum.

In this case, a plastic pipe with excellent heat resistance is laid in advance in the tunnel or conduit where the power cable is laid, and the above-mentioned optical fiber is fed under pressure into the pipe to serve as a temperature distribution measurement sensor, and the optical fiber is used as a sensor for measuring temperature distribution. It is preferable to detect a failure point from the temperature distribution of the fiber.

0010

[Operation] An optical fiber is laid along the power cable installation route, and the longitudinal temperature distribution of the power cable installation route is measured from the backscattered light distribution of the optical fiber. In this case, the temperature distribution in the longitudinal direction inside the tunnel or pipe may differ even under normal conditions without any ground faults, and the highest temperature detection point of the measured temperature distribution should be determined to be the failure point. It is not possible. Therefore, first, it is determined that an accident has occurred when a trip signal of the underground power transmission line is received, and this is used as a trigger signal to immediately measure the temperature distribution in the longitudinal direction of the optical fiber. Then, the difference value of the temperature distribution before and after receiving the trip signal, that is, the instantaneous temperature rise, is determined, and the distance position corresponding to the position where this difference value is maximum is determined as the failure point. As a result, the influence of temperature distribution under normal conditions is removed, and the accident location, including the cable connection, can be accurately located.

[0011] With the arc energy etc. at the time of the earth fault energy,
Although it is possible that the optical fiber may be disconnected, in this case, the position of the disconnection, that is, the ground fault point can be detected from the measured backscattered light distribution. Therefore, according to this method, a ground fault point can be detected from the backscattered light distribution when the optical fiber is broken when a ground fault occurs, and from the temperature distribution when the optical fiber is not broken.

0012

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

FIG. 1 shows a configuration of an embodiment of the method for detecting a fault point in an underground power transmission line according to the present invention.

In the figure, 1 is an optical fiber, and 2 is an OT obtained from the distribution waveform of Raman backscattered light by this optical fiber 1.
This is a temperature distribution measuring device that measures temperature distribution along an optical fiber 1 using the DR method. Reference numeral 3 denotes a three-phase power cable that transmits power from the power transmission side to the power reception side, which is indicated by a power source 4, and in reality, as shown in FIG. 3, a plurality of lines are laid in the tunnel 10. In the tunnel 10 where this power cable 3 is laid,
A plastic pipe 8 having excellent heat resistance is attached to the center of the upper part and laid in advance along the tunnel 10. The optical fiber 1 is placed in advance in this plastic pipe 8 as shown in FIG.
The wire is then extended along the tunnel 10 as a sensor for measuring temperature distribution.

[0015] The temperature distribution measuring device 2 uses this optical fiber 1.
is connected to one end of the temperature distribution measuring device 2, and inputs laser pulse light into the optical fiber 1 from a light source inside the temperature distribution measuring device 2, and detects Raman scattered light pulses, which are backscattered light generated within the optical fiber 1, in a time-division manner. By doing this, the longitudinal distribution of Raman scattered light is obtained, and by utilizing the fact that the intensity of this Raman scattered light depends on temperature, the temperature distribution is obtained over the total length of the power cable 3 in which the optical fiber is installed. .

5 is a current transformer attached to each phase u, v, w of the 3-phase AC single circuit of the power cable 3; 6 is the current transformer 5;
This is a trigger signal generator that receives a trip signal in the underground transmission line system from the current value obtained from the current value, detects the occurrence of a fault such as a ground fault, and gives a trigger signal to the temperature distribution measuring device 2 to start measurement. . 7 is a data processing device that evaluates the temperature distribution signal obtained by the temperature distribution measuring device 2 and locates a fault point on the power cable 3;
compares the temperature distribution after receiving the trip signal, that is, the temperature distribution measured by the temperature distribution measuring device 2 upon receiving the trigger signal, with the temperature distribution signal that was already measured before receiving the trip signal, The difference value of the temperature distribution before and after receiving the trip signal is determined, and the position where this difference value is maximum is detected as the failure point.

[0017] If a ground fault occurs in the power cable 3 shown in Fig. 1 due to deterioration of the insulation or external trauma, a large current will flow into the ground system at the ground fault point, and the power cable 3 will be severely damaged by the energy generated at this time. At the same time, the ambient temperature rises temporarily due to the arc energy, reaching a peak at the ground fault point. Prior to this, the trigger signal generator 6 monitored the current value obtained from the current transformer 5 attached to the power cable 3, and current information corresponding to the failure was obtained as a trip signal for the underground power transmission line. If so, generate a trigger signal. Upon receiving this trigger signal, the temperature distribution measuring device 2 immediately starts measurement and measures the temperature distribution in the longitudinal direction of the optical fiber 1 laid along the tunnel 10. The data processing device 7 stores in advance the temperature distribution obtained from the temperature distribution measuring device 2 during normal times without any ground faults, etc. or the temperature distribution immediately before the trigger signal is generated, and the stored temperature distribution signal The temperature distribution measured after receiving the trigger signal is compared with the temperature distribution, the difference value between the two is determined, and the position where the difference value of the temperature distribution is the maximum is located as the failure point. FIG. 4 shows temperature distribution data obtained from a simulated ground fault accident experiment, and the ground fault point x can be found from the temperature peak position P.

[0018] In this way, the temperature distribution measuring device 2 starts measurement only when current information corresponding to the failure is obtained, and the instantaneous temperature rise is detected from the difference value of the temperature distribution before and after that. After clearly recognizing that a failure has occurred, it is possible to detect the failure point with high accuracy without being affected by temperature distribution during normal operation.

[0019] In order to determine the failure point from continuous temperature distribution information along the power cable installation section, underground power transmission lines in operation are constantly monitored and all failures are detected at all locations, including the power cable connection points. can be detected. In addition, if the optical fiber breaks due to arc energy during a ground fault,
The ground fault point, which is the position of the disconnection, can be determined from the measured backscattered light distribution. Therefore, reliability is high.

[0020] Since only one optical fiber is required to be installed along the power cable installation route, it is highly economical, and since the optical fiber is installed later under pressure into the pipe,
If only the optical fiber is damaged due to thermal effects during a ground fault, the optical fiber only in the vicinity of the ground fault can be easily replaced and reinstalled. Furthermore, since the failure point can be located simply by placing the device at the end of the installed optical fiber, there is no need for new construction and it can be easily applied to existing wire connections.

[0021] In the above embodiment, a case has been described in which an optical fiber is installed in a tunnel in which a power cable is installed, but the present invention can be similarly applied to a case in which an optical fiber is installed in a conduit.

[0022]

As described above, according to the invention as claimed in claim 1, (1) after receiving a trip signal of an underground power transmission line, an instantaneous temperature rise can be detected based on the difference value between the temperature distribution before and after the trip signal. Since the location of the fault is determined by detecting the location of the fault, it is possible to detect the fault point quickly and accurately without being affected by temperature distribution during normal conditions. (2) Since the failure point is determined from continuous temperature distribution information along the power cable installation section, all failures can be detected at all locations including the power cable connection section. In particular, even when an optical fiber is disconnected when a ground fault occurs, the ground fault point can be detected from the backscattered light distribution. (3) Only one optical fiber is required along the power cable installation route, which is highly economical. Furthermore, since the point of failure can be located simply by placing the device at the end of the installed optical fiber, there is basically no need for new construction, and it can be easily applied to existing wire connections.

Furthermore, according to the invention as claimed in claim 2, since the optical fiber can be force-fed and installed into the pipe later, if only the fiber is damaged due to the thermal effect at the time of a ground fault, only the area near the ground fault point is damaged. Optical fibers can be easily replaced.

[Brief explanation of drawings]

[Fig. 1] Block diagram of a device to which the underground power transmission line failure point detection method according to the present invention is applied.

[Figure 2] Cross-sectional view of the optical fiber temperature distribution measurement sensor used in Figure 1

[Figure 3] Cross-sectional view of a tunnel showing an example of optical fiber installation

[Figure 4]
Diagram showing an example of temperature distribution measurement results during a simulated ground fault accident

[Explanation of symbols]

1 Optical fiber 2 Temperature distribution measuring device 3 Power cable 4 Power supply 5 Current transformer 6 Trigger signal generator 7 Data processing device 8 Plastic pipe 10 Cave road

Claims (2)

[Claims] Claim 1: An optical fiber is installed in a tunnel or conduit where a power cable is installed, and the temperature distribution in the longitudinal direction inside the tunnel or conduit is measured from the backscattered light distribution of the optical fiber. In a fault point detection method for underground power transmission lines that detects fault points from distribution, after receiving a trip signal from an underground power transmission line, this is used as a trigger signal to immediately measure the temperature distribution in the longitudinal direction of the optical fiber, and the trip signal is detected. A method for detecting a fault point in an underground power transmission line, characterized in that the difference value of temperature distribution before and after reception is determined, and the fault point is detected from the position where the difference value is maximum. 2. A plastic pipe with excellent heat resistance is laid in advance in a tunnel or conduit where a power cable is laid, and the optical fiber is fed under pressure into the pipe to serve as a sensor for measuring temperature distribution, and the optical fiber is used as a sensor for measuring temperature distribution. 2. The method for detecting a fault point in an underground power transmission line according to claim 1, wherein the fault point is detected from the temperature distribution of the underground power transmission line.