JPH10267984A - Detecting system for accident point in underground transmission line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detecting system, for an accident point in an underground transmission line, which can be realized at low costs. SOLUTION: An optical fiber 11 for a sensor is fixed to one or more connection parts 98 on an underground transmission line so as to be along them, and a detecting device 4 which detects the accident in any connection part 98 on the basis of a change in the optical characteristic of the optical fiber 11 for the sensor is connected optically to one end of the optical fiber 11 for the sensor. The optical characteristic of the optical fiber 11 for the sensor is changed due to the instantaneous expansion of any connection part 98 in which an accident is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for detecting a fault point on an underground transmission line, and more particularly to a fault detection system for an underground transmission line which can be realized at low cost.

[0002]

2. Description of the Related Art A conventional underground transmission line fault section locating system will be described with reference to FIG.

[0003] As shown in the figure, an underground transmission line is constituted by three power cables. Each power cable 97
Are connected by a connection part 98 every several hundred meters. An optical magnetic field sensor 91 is attached to each connection part 98 so that a current flowing through the connection part 98 at the time of an accident can be detected by magnetic field measurement. A signal detection unit 93 connected to the optical magnetic field sensor 91 by an optical fiber 92 measures the outputs of the optical magnetic field sensor 91 for three phases, and combines them to measure a zero-phase current. . The zero-phase current measured by the signal detection unit 93 is input by a transmission device 94 via a signal transmission optical fiber 95 to a central monitoring device 96 installed in a monitoring station. Central monitoring device 9
Reference numeral 6 designates a section in which an accident has occurred by comprehensively analyzing the zero-phase current measurement results at a plurality of locations.

[0004] A ground fault may occur anywhere along the entire length of the underground power transmission line, but generally has a low probability of occurrence in the cable section and almost always occurs in the connection section. Therefore, it is considered that the ground fault can be almost detected by knowing at which connection point the accident has occurred.

[0005]

However, in the conventional system, it was necessary to install a current sensor (optical magnetic field sensor in the above example) in the sinus and transmit the outputs of a plurality of optical magnetic field sensors to a monitoring station. The cost of the system was high. Although such a system can be applied to underground power transmission lines that are important and costly, there is a problem in terms of cost when used for general purposes.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide an underground transmission line fault point detection system which can be realized at low cost.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an optical fiber for a sensor fixed along one or more connecting portions of an underground power transmission line, and one end of the optical fiber for a sensor. In addition, a detection device for detecting an accident at the connection portion from a change in the optical characteristics of the sensor optical fiber is optically connected.

The sensor optical fiber may be sequentially connected to a common lead optical fiber, and the detection device may be connected to one end of the lead optical fiber.

[0009] At the opposite end of the sensor optical fiber, a fold-back means may be connected to fold the propagation light of the sensor optical fiber.

The detection device has a light source for transmitting light to the sensor optical fiber and a light receiving unit for receiving the return light, and has means for analyzing the received light in time in synchronization with the operation of the light source. Is also good.

[0011]

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

As shown in FIG. 1, an underground transmission line to which the accident point detection system of the present invention is applied has an outer diameter of about 150 m.
connection part 98 having an outer diameter of about 300 mm
Is provided. The sensor optical fiber 11 of the present invention is wound around the connection portion 98 while being shifted in the axial direction along the outer periphery. The winding pitch is about 10
0 mm. The optical fiber 11 for the sensor is connected to the connecting portion 98.
Are fixed at a plurality of locations by fixing bands (not shown). One end of the sensor optical fiber 11 is connected to a lead optical fiber via an optical branch (not shown).
To the opposite end of the optical fiber for sensor 11 is connected a folding means 21 for folding back the propagation light of the optical fiber for sensor 11.

As shown in FIG. 2, the sensor optical fiber 11 at the connection portion in FIG. 1 is connected to the lead optical fiber 1 via an optical splitter 31 provided on the lead optical fiber 1. . The splitting ratio of the optical splitter 31 is, for example, 10
In this case, 10 out of the light from the near end side (left side in the figure) of the optical fiber for lead 1 is used.
% Of the light is split into the sensor optical fiber, and the remaining 90%
% Light is branched toward the far end. The folding means 21 is provided with a reflector made of a vapor-deposited film of gold or the like at a portion where the tip of the optical fiber is cut at a right angle, and the light propagating through the sensor optical fiber in the direction of A is reflected by reflection to be folded. The propagation optical fiber propagates in the direction of B.

As shown in FIG. 2, sensor optical fibers 12, 13, provided at each connection portion in the same manner as in FIG.
Reference numeral 14 is connected to the lead optical fiber 1 via optical splitters 32, 33, and 34 which are sequentially provided on the far end side of the optical fiber 1 for read from the optical splitter 31. 22, 23,
Numeral 24 denotes each turning means.

At one end (near end) of the optical fiber 1 for reading, a detecting device 4 of the present invention is provided, and this detecting device 4 is composed of the optical fiber 1 for reading and the optical splitters 31 and 3.
Optical fibers 11, 1 for each sensor via 2, 33, 34
2, 13, and 14 are optically connected. Although not shown, the detection device 4 includes a light source for transmitting light to each sensor optical fiber and a light receiving unit for receiving return light thereof, and has a means for performing a time analysis in synchronization with the operation of the light source. And optical fibers 11, 12, 13, 14 for each sensor.
It has a function to detect an accident at each connection part from a change in the optical characteristics of the connection part. Specifically, the detection device 4 uses an OTDR that measures a loss distribution (light intensity distribution) of an optical fiber. The detection device 4 can detect a disconnection or an increase in loss of the sensor optical fiber.

Next, the operation will be described.

From the detection device 4 provided with the OTDR, pulsed light is emitted at regular time intervals. The pulsed light first enters the optical fiber 1 for reading, and is scattered in the optical fiber 1 by backscattered light (approximately 1 / 100,000 of the amount of light reached).
). The 10% light amount of the pulse light that has reached the optical splitter 31 is split into the sensor optical fiber 11. Then, it is almost 100
The pulse light returned after being% -folded is incident on the optical splitter 31 from the opposite direction. The pulse light returned in this way is received by the detection device 4 via the optical fiber for read 1. The pulse light branched toward the far end by the optical splitter 31 sequentially reaches the optical splitters 32, 33, and 34, and 10% of the amount of the light reaches the optical fibers 12, 13, and 10 for the sensor. 14 and return means 22 and 2
The pulse light returned at 3 and 24 and returned is received by the detection device 4 via the read optical fiber 1.

FIG. 3 shows a time change of the light received by the detecting device 4.
Shown in In FIG. 3, the horizontal axis represents time, and the vertical axis represents optical signal intensity (logarithm). In the OTDR, an optical signal intensity measured as a function of time is converted into a distance by an optical propagation speed in an optical fiber. The time axis and the distance axis are essentially the same. Therefore, in FIG. 3, the horizontal axis may be read as distance.

As shown in FIG.
The backscattered light returning from the optical fiber has a waveform 8 that attenuates at a constant rate with time (distance) due to the transmission loss of the optical fiber.
It becomes 0. Since the light propagating through the optical fiber for reading 1 is attenuated by the branching ratio in the optical branching unit in addition to the transmission loss of the optical fiber, a step is formed in the waveform 80 (for example, a step 831 generated in the optical branching unit 31). . On the other hand, the folding means 21, 21 of the optical fibers 11, 12, 13, 14 for each sensor are used.
The pulse light turned back at 2, 23, 24 has a higher intensity than the backscattered light, so that the peak 821,
822, 823, 824.

By the way, during normal times when no accident has occurred,
A waveform as shown in FIG. 3 is obtained. Next, an operation and a waveform when a ground fault occurs at a connection portion of the underground power transmission line will be described with reference to FIGS.

As shown in FIG. 4, when a ground fault occurs at the connection portion 98, the connection portion 98 instantaneously expands as shown by a dotted line due to the energy rapidly discharged in the connection portion 98. Then, a strong tension is instantaneously applied to the sensor optical fiber 11 wound around the connection portion 98, and the sensor optical fiber 11 cannot withstand this tension and breaks, for example, at a cross mark in the drawing. Then, the pulse light does not propagate to the sensor optical fiber 11 after the X mark part, and the pulse light does not reach the folding means 21. Accordingly, as shown in FIG. 5, the waveform of the light received by the detection device 4 is a waveform 80X in which the peak 821 due to the turning light from the turning means 21 has disappeared. Thus, it can be seen that the sensor optical fiber 11 corresponding to the peak 821 has been disconnected.

If the detection device 4 detects the presence or absence of the peaks 821, 822, 823, 824 due to the return pulse light from the return means 21, 22, 23, 24, the point at which the ground fault accident occurs (Connection part 98) can be located.

Next, another embodiment will be described.

As shown in FIG. 6, as a structure of the folding means 21, an optical splitter 38 is connected to the end of the sensor optical fiber 11 opposite to the detection device 4, The two ports may be connected to each other. The light from the detection device 4 may be output from the port C of the optical branching device 38 and returned to the port D, or may be output from the port D and returned to the port C. It will be folded back to the fiber 11.

Further, as shown in FIG.
As one configuration, the detecting device 4 for the sensor optical fiber 11
Alternatively, the optical circulator 39 may be connected to the opposite end, and the output port of the optical circulator 39 may be connected to another input port. Light from the detection device 4 is input from the port E of the optical circulator 39 and output to the port F. This light is input from the port G and output to the port E, and is returned to the sensor optical fiber 11. Optical splitter 3
Compared with the configuration of FIG.
Is expensive, but is advantageous in this respect because the insertion loss is small.

In the above embodiment, each optical splitter 3
Although the branching ratios of 1, 32, 33, and 34 were all the same,
The ratio of branching to the sensor optical fiber may be set to be smaller as the position is closer to the detection device 4. By doing so, it is possible to relatively increase the intensity of the reflected light from the distant return means, as compared with the case where all the branching ratios are kept constant.
It is also possible to make the returning light intensities from all the turning means substantially the same.

In the above embodiment, the case where the sensor optical fiber 11 wound around the connection portion 98 is broken due to a ground fault has been described.
If a loss of about dB or more occurs, the OT at the time of the accident
By comparing the DR waveform with the OTDR waveform before the accident, it is possible to locate the point (connection part 98) where the ground fault has occurred.

In the above embodiment, the OTDR which measures the loss distribution in the length direction of the optical fiber as a function of time is used as a detecting device for detecting a disconnection or an increase in loss of the optical fiber for the sensor. Other types of detection devices can be used as long as they can be used for measuring the loss distribution in the length direction. For example, an OFDR (Optical Frequency Domain Refl) that measures the loss distribution in the length direction of an optical fiber as a function of frequency.
ectometry) can be used.

Further, in the above-described embodiment, the sensor optical fiber 11 is wound around the connecting portion 98. However, the sensor optical fiber 11 may be fixed along the connecting portion 98 with a fixed band. A ground fault can be detected by causing a disconnection.

The lead optical fiber 1 used in the present invention can be used for transmitting information for other purposes. For example, as shown in FIG. 8, the optical splitters 51, 52,
53 is added to these optical splitters 51, 52 and 53.
The TV image transmission devices 71, 72 and 73 are connected. Further, the image receiving device 42 is installed at the monitoring station together with the detecting device 4 so that the optical switching device 41 can switch and use the image receiving device 42 and the detecting device 4. In this manner, the image receiving device 42 is normally connected to the lead optical fiber 1 and used for monitoring by an image, and when an accident occurs, the detecting device 4 is connected to the lead optical fiber 1 to detect an accident point. It can be operated as if it were.

[0031]

The present invention exhibits the following excellent effects.

(1) Since it is not necessary to install an expensive current sensor for each connecting portion as in the conventional case, and an inexpensive optical fiber for the sensor may be installed, the fault point detection of the underground power transmission line can be performed as compared with the conventional case. It can be performed at low cost.

(2) Further, since a transmission device for grasping the information of the sensor section at the monitoring station is not required, the cost can be reduced also in this respect.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a connection portion of an accident point detection system according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of an accident point detection system having a plurality of connection units in FIG.

FIG. 3 is a diagram of an OTDR waveform measured by a detection device of the fault point detection system of FIG. 2;

FIG. 4 is a diagram showing a behavior of the connecting portion of FIG. 1 at the time of an accident.

FIG. 5 is a diagram of an OTDR waveform at the time of an accident measured by a detection device of the accident point detection system of FIG. 2;

FIG. 6 is a configuration diagram of a folding unit according to another embodiment of the present invention.

FIG. 7 is a configuration diagram of a folding unit according to another embodiment of the present invention.

FIG. 8 is a configuration diagram of an application system of the present invention.

FIG. 9 is a configuration diagram of a conventional fault section locating system for an underground transmission line.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber for leads 4 Detector 11, 12, 13, 14 Optical fiber for sensor 21, 22, 23, 24 Folding means 98 Connection part

Claims (4)

[Claims] 1. An optical fiber for a sensor is fixed along one or more connection portions of an underground power transmission line along one end of the optical fiber for a sensor based on a change in optical characteristics of the optical fiber for a sensor. An underground transmission line fault point detection system, wherein a detection device for detecting an accident in a part is optically connected. 2. The underground power transmission line according to claim 1, wherein said sensor optical fiber is connected to a common lead optical fiber in sequence, and said detecting device is connected to one end of said lead optical fiber. Accident point detection system. 3. An underground transmission line path fault detection system according to claim 1, wherein a return means for turning back the propagation light of the sensor optical fiber is connected to the opposite end of the sensor optical fiber. system. 4. The detection device has a light source for transmitting light to the sensor optical fiber and a light receiving unit for receiving return light thereof, and has means for performing time analysis in synchronization with the operation of the light source. The underground power transmission line fault point detection system according to claim 1, wherein: