JPS6236414B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transmission path fault location detection method for detecting the location of faults such as electrical leakage and damage in a transmission path.

When a failure such as electric leakage or damage occurs in the transmission line,
It is necessary to detect the location of the leakage or damage, and to switch the transmission path.

Therefore, as a conventional method for detecting the location of a fault in a transmission line, ammeters are installed at appropriate intervals on the transmission line, and when excessive current flows due to leakage or damage, the corresponding section is detected using the ammeter. A heat detection method was used in which heat detectors were installed at appropriate intervals on the transmission line to detect the location of the heat generated due to electrical leakage, damage, etc.

However, the conventional current monitoring method and heat detection method for detecting the location of electric leakage, damage, etc. in a transmission line have the following drawbacks. That is, since ammeters or heat detectors are provided at appropriate intervals along the transmission line, there is a drawback that the location of leakage or damage in the transmission line changes only over a general section.

The present invention aims to eliminate such conventional drawbacks as described above and to accurately detect the location of faults such as electric leakage and damage in the transmission line, and provides a transmission line fault location detection method for detecting the location of the fault in the transmission line. ,
An optical fiber covered with a coating that shrinks due to heat is provided near the transmission line, a pulsed optical signal is inputted to the optical fiber from a terminal station, and changes in the amount of light of the optical signal traveling backwards are detected at the terminal station. The system is characterized in that it monitors and detects the location of a fault in the transmission path.

An embodiment of the present invention will be described in detail with reference to FIGS. 1 to 3.

FIG. 1 is a diagram showing an example in which an optical fiber covered with a heat-shrinkable coating is provided near a transmission line. In the figure, 1 is a transmission path, 2 is a heat-shrinkable coating, and 3 is an optical fiber.

FIG. 2 is a diagram showing an example of an optical fiber bent due to a failure in a transmission path. In the figure, 1
3 are the same numbers as in FIG. 1, and 4 is the faulty part.

FIG. 3 is a block diagram of a device on the optical input side that detects the location of a fault in a transmission line. In the figure, 5 is an input terminal, 6 is an optical-to-electrical converter, 7 is a processing section, and 8
is a position indicator.

FIG. 4 is a diagram showing the characteristics of the amount of light of a retrograde optical signal and the round trip time from the time of optical signal input to the light input side. In the figure, a shows the characteristics when the transmission path is normal, and b shows the characteristics when a failure occurs in the transmission path. Further, the horizontal axis x represents the round trip time from the input of the optical signal to the arrival of the optical signal traveling backward to the optical input side, and the vertical axis y represents the amount of light of the optical signal traveling backward.

As shown in FIG. 1, an optical fiber 3 covered with a heat-shrinkable coating that shrinks due to heat is placed near the transmission line 1.
is provided to input a pulsed optical signal to the optical fiber 3. This optical signal is transmitted through the optical fiber 3 while being refracted. Further, at this time, the optical signal collides with the particles constituting the optical fiber 3, which causes Lilley scattering, and a phenomenon occurs in which a portion of the signal travels backward. The more the optical signal collides with the particles of the optical fiber near the optical input end, as shown in Figure 4a, the more
That is, the shorter the round trip time from the input of the optical signal to the arrival of the optical signal traveling backward to the optical input side, the greater the amount of light. This is because the longer the distance at which the optical signal collides with the particles of the optical fiber, that is, the longer the round trip time, the more times the retrograde optical signal will collide with the particles of the optical fiber again, and the amount of light will attenuate.

The above-mentioned retrograde optical signal is extracted by a half mirror at the optical input end and input to the optical-to-electrical converter 6. The retrograde optical signal is converted into a current value by an optical-to-electrical converter 6 and input to a processing section 7. Processing section 7
Now, the change in the current value of the retrograde optical signal per pulse is monitored while corresponding this current value to the round trip time from the optical input terminal to the retrograde point of the optical signal. That is, as can be seen from FIG. 4a, the current value and the round-trip time are inversely proportional, so by differentiating the current value with respect to the round-trip time, rapid changes in the differential value are monitored.

Now, as shown in FIG.
When a fault such as electrical leakage or damage occurs in the faulty part 4, heat is generated. The heat shrinks the heat-shrinkable coating 2 and applies tension to the optical fiber 3, causing the optical fiber 3 to bend. When the optical fiber 3 is bent in this way, mode scattering occurs at the bending point,
The optical signal attenuates rapidly. For this reason, the retrograde optical signal due to Leeley scattering occurring after the bending point also rapidly attenuates. As a result, the amount of light of the optical signal that goes backwards after the bending point of the optical fiber 3 input to the optical input section is also attenuated, as shown in FIG. 4b.
Therefore, the value obtained by differentiating the current value in the processing section 7 also decreases. In the processing unit 7, when the round trip time when this differential value decreases is t, and the speed of light in the fiber is c, the distance l from the optical input end to the failure point is calculated as l=1/2t・c, and the calculated distance l is displayed on the position display 8.

With the above, the location of a fault in the transmission path can be detected. That is, according to the present invention, since the location of a fault in a transmission path is accurately detected, it is possible to obtain the effect of immediately dealing with the problem in terms of security.

[Brief explanation of the drawing]

Fig. 1 shows an example of an optical fiber covered with a heat-shrinkable coating provided near the transmission path, and Fig.
A diagram showing an example of an optical fiber bent due to a fault in the transmission line. Figure 3 is a block diagram of a device on the optical input side that detects the position of a fault in the transmission line. Figure 4 shows the amount of light of a backward optical signal. FIG. 4 is a diagram showing the characteristics of the round trip time from the time of optical signal input to the optical input side. In the figure, 1 is a transmission line, 2 is a heat-shrinkable composite,
3 is an optical fiber, 4 is a failure part, 5 is an input terminal, 6
is an optical-to-electrical converter, 7 is a processing unit, 8 is a position indicator, x is a round trip time from the time of optical signal input to the optical input side, and y is the amount of light of the optical signal traveling backward.

Claims (1)

[Claims] 1. In a transmission line fault location detection method that detects the location of a fault in a transmission line, an optical fiber covered with a coating that shrinks due to heat is provided near the transmission line, and pulses are transmitted from the end of the optical fiber to the optical fiber. 1. A method for detecting a fault position of a transmission line, characterized in that the position of a fault in the transmission line is detected by inputting an optical signal and monitoring changes in the amount of light of the optical signal traveling backward at the end of the transmission line.