JPH0220073B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lightning strike area detection method, and more particularly to a lightning strike area detection method suitable for detecting a lightning strike area using a polarization preserving optical fiber.

Since the damage caused by lightning to overhead power transmission lines is very large, it is important to explore the sections where lightning strikes occur. By the way, the conventional method for detecting areas struck by lightning has a system configuration in which a current transformer is installed on each tower to detect lightning current, and comprehensive monitoring is performed at a terminal station. However, in this case, not only a power source is required for each tower, but also a microcomputer or the like is required at the terminal station. Additionally, in order to avoid the effects of electromagnetic induction, it has been considered to convert the lightning signal into light and transmit it, but this would require an additional optical transmitter, which would generally be expensive. This results in the following drawbacks.

The present invention has been made in view of the above, and its purpose is to detect lightning strikes using a polarization-maintaining optical fiber that can detect lightning strikes without a power source and centrally monitor the lightning strike area. The object of the present invention is to provide a section detection method.

A feature of the present invention is that an optical transmission line made of a polarization-maintaining optical fiber is provided between a transmitting end and a receiving end, a linearly polarized light wave is transmitted through this optical transmission line, and a first optical fiber is provided in the middle of the optical transmission line. A plurality of optical systems each consisting of a microlens, a Faraday element, a polarizing beam splitter, and a second microlens are sequentially provided, and a lightning current is passed through the coil of the Faraday element to rotate the plane of polarization of the light wave passing through it by 90 degrees. There was no such thing,
The orthogonal polarization components from the polarization beam splitter are bypassed by a bypass section consisting of a third microlens, a polarization preserving optical fiber, and a fourth microlens, and the light waves from the fourth microlens are The polarizing beam is guided to the second microlens via a polarizing beam splitter or a separately provided polarizing beam splitter, and the length of the polarization maintaining optical fiber in the bypass section is changed for each optical system, and the receiving At the end, the delay time from when the received light wave is interrupted to when the light wave that has passed through the bypass section is received is measured, and from this delay time it is determined which of the above optical systems has been struck by lightning. , the point is that it detects lightning strike areas.

Examples of the method of the present invention will be described in detail below with reference to FIGS. 1 to 3.

FIG. 1 is a diagram of an apparatus for explaining one embodiment of the method of the present invention. In FIG. 1, 1 and 2 are relay terminal stations, 1 is a transmitting end, and 2 is a receiving end.
Reference numeral 3 denotes an optical cable having a built-in elliptical jacket-type polarization-maintaining optical fiber for the 1.3 μm band, which is provided between the transmitting end 1 and the receiving end 2, and constitutes an overhead or ground-wire optical transmission line. At the transmitting end 1, the semiconductor laser light is linearly polarized, and the linearly polarized light is incident on one of the two unique orthogonal polarization axes of the polarization-maintaining optical fiber, for example, in the long axis direction.

4 ₁ to 4n each indicate a steel tower, and the steel towers 4 ₁ to 4
An optical system consisting of a first microlens 5, a Faraday rotation element 6, polarization beam splitters 7a, 7b, and a second microlens 8 provided in the middle of the optical transmission line 3 is provided at each of the optical systems. and,
The coil 9 of the Faraday rotation element 6 is struck by lightning 10.
When a lightning strike occurs, a current clipper 11 causes a lightning current whose peak value is held constant to flow, thereby rotating the plane of polarization of the light wave passing through the Faraday rotation element 6 by 90 degrees. The light waves of orthogonal polarization components (light in the right angle direction) generated by the polarization beam splitter 7a due to the lightning strike are transmitted to the third microlens 12, the polarization preserving optical fiber 13, and the fourth microlens 14.
Bypass is provided by a bypass section consisting of: Note that the bypass light is linearly polarized light from the microlens 12 that is incident on the short axis direction of the polarization preserving optical fiber 13, and the light wave from the microlens 14 is guided to the second microlens 8 via the polarization beam splitter 7b. It's like this.

Therefore, when there is no lightning strike, the light wave from the optical transmission line 3 passes through the microlens 5, the Faraday rotation element 6, the polarizing beam splitters 7a and 7b, the microlens 8, and the optical transmission line 3. When lightning strikes, the light is transmitted to the microlens 5, the Faraday rotation element 6, the polarizing beam splitter 7a, the microlens 12, the polarization preserving optical fiber 13, the microlens 14, the polarizing beam splitter 7b, the microlens 8, and the optical transmission line 3. and proceed. Therefore, as shown in Fig. 2, the light output of the light wave received at the receiving end 2 becomes zero when the light is interrupted for the duration time t of the lightning current waveform for ₁ second, and then becomes the normal light when there is no lightning strike. After the time t ₂ seconds, which is determined mainly by the length l of the polarization-maintaining optical fiber 13 in the bypass section, the light wave that has passed through the bypass section is also received, so this is superimposed on the above normal optical output. . Note that if the propagation speed of light in the polarization-maintaining optical fiber 13 is V (=speed of light/1.46), then t ₂ =l/V. Therefore, the polarization preserving optical fiber 13 in the bypass section of the optical system provided for each steel tower 4 ₁ to 4n
If we change the length of and make t ₂ different, we get
By measuring _t2 , it is possible to determine which steel tower was struck by lightning and to detect the area where the lightning struck. Note that t ₁ is usually about 40μsec, and t ₂ is l=
At 1 km, it is 5 μsec.

According to the embodiment of the present invention described above, it is possible to reliably detect the lightning strike section, and moreover, the lightning strike section can be detected _reliably .
A power supply is not required for the optical system provided in the 4n for detecting lightning current, and central monitoring can be performed at the terminal station. Furthermore, since it uses light, it is not affected by electromagnetic induction.

FIG. 3 is a configuration diagram showing another example of the optical system installed in each steel tower in FIG. 1 for explaining another embodiment of the method of the present invention, and the same parts as in FIG. 1 are designated by the same reference numerals. , the explanation is omitted here. In Figure 3, there is only one polarizing beam splitter,
The light separated perpendicularly by the polarizing beam splitter 7 is sent to a microlens 12 and a polarization preserving optical fiber 1.
3. The light is returned to the polarizing beam splitter 7 through the microlens 14. Even in this case, the same effect as in the case of FIG. 1 can be obtained.

As described above, according to the present invention, lightning can be detected without a power source, and the lightning strike area can be centrally monitored.

[Brief explanation of drawings]

Fig. 1 is a device diagram for explaining one embodiment of the lightning strike zone detection method of the present invention, Fig. 2 is a waveform diagram of the received optical output during a lightning strike, and Fig. 3 is another embodiment of the method of the present invention. FIG. 2 is a configuration diagram showing another example of the optical system provided in each steel tower in FIG. 1 for explaining. 1: Transmitting end, 2: Receiving end, 3: Optical transmission line, 4 ₁
~4n: Steel tower, 5, 8, 12, 13: Microlens, 6: Faraday rotation element, 7, 7a, 7
b: Polarizing beam splitter, 9: Coil, 10:
Lightning strike, 11: Current clipper, 14: Polarization preserving optical fiber.

Claims (1)

[Claims] 1. An optical transmission line made of a polarization-maintaining optical fiber is provided between a transmitting end and a receiving end, a linearly polarized light wave is transmitted through the optical transmission line, and a first microlens, a Faraday element, A plurality of optical systems each consisting of a polarizing beam splitter and a second microlens are sequentially provided, and a lightning current is applied to the coil of the Faraday element to change the polarization plane of the light wave passing therethrough.
The orthogonal polarization components from the polarization beam splitter are bypassed by a bypass section consisting of a third microlens, a polarization preserving optical fiber, and a fourth microlens, and the fourth microlens is rotated by 90 degrees. The light wave from the microlens is guided to the second microlens via the polarization beam splitter or a separately provided polarization beam splitter, and the length of the polarization maintaining optical fiber of the bypass section is set to the length of each of the polarization maintaining optical fibers. At the receiving end, the delay time from when the received light wave is interrupted until the light wave that has passed through the bypass section is received is measured, and from this delay time it is determined which optical system among the optical systems is used. A method for detecting a lightning strike area, characterized by determining whether a lightning strike occurred and detecting a lightning strike area.