JPS61107169A - Current detector using optical fiber - Google Patents

Abstract

PURPOSE:To enable the detection of a current with high accuracy and to simplify a structure, by detecting a current in such a mode that the magnetic field around an electric wire is subjected to perimetric integration. CONSTITUTION:The polarizing axes of two polarization surface preserving optical fibers 4, 4 are arranged so as to be mutually inclined by 45 deg. in the coupling with polarization beam splitters 2, 2 and the beam emitted from a laser beam source 5 is divided into two beam paths by the splitters 2, 2. When the beams passed through the fibers 4 are incident to single mode optical fibers 31, said beams are rotated by an angle phi by the magnetic field generating from an electric wire 11 to enter an 1/2 wavelength plate 8 to generate phase shift of 180 deg. and further propagated through the fibers 31 to be rotated by the angle phi to be incident to light receiving elements 61, 62 through the fibers 4 and the splitters 2. The ratio of the sum and difference of orthogonal components of the optical signals from the elements 61, 62 is calculated by a subtraction amplifying circuit 71, an addition amplifying circuit 72 and a divider 73 and the obtained output is proportional to the current of the electric wire 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a current detector using an optical fiber.

[Prior Art] Conventionally, a wire-wound current transformer (CT), as shown in FIG. 5, has been widely used as a detector for detecting the current flowing in a power transmission line. This consists of a primary winding 1 protected by an insulator 12.
3, an iron core 14, a secondary winding 15, a measurement terminal 16, an insulating filling 17, and a current transforming element 10. However, as power transmission voltages have increased, current transformers have also become larger and more expensive.

In recent years, the practical use of optical fibers has progressed rapidly, and a current detector as shown in FIG. 6, which utilizes the electro-optical effect of magnetism, that is, the Faraday effect, has been proposed and put into practical use. That is, a Faraday element 25 is provided close to the magnetic field H generated by the current flowing through the electric wire 11, and the light is emitted and guided to the optical fiber 21 connected to the detector 26, and the emitted light is transmitted through the polarizer 23. The light enters the Faraday element 25, and the light whose polarization plane has been rotated by the magnetic field H within the Faraday element 25 enters the optical fiber 22 via the analyzer 24. By detecting the rotation angle of the light, the current is This attempts to detect the current value from the rotation angle, which is proportional to the strength.

[Problems to be Solved by the Invention] The optical fiber-based current detector described above is smaller and more economical than the conventional current transformer type shown in FIG. 5, but it still has the following problems. There is.

In other words, the first is that it is affected by disturbances such as the influence of magnetic fields due to other phase currents, the second is that the accuracy of the distance from the power transmission line to the installation position directly affects the detection accuracy, and the third is that 7? The problem is that extra optical components such as a polarizer and an analyzer are required before and after the Radday element.

Therefore, there has been a strong demand for an optical current detector that does not have the above-mentioned problems, has the same accuracy as the conventional wire-wound detector, and has a simple structure.

[Means for Solving the Problems] The present invention has been made in view of the above-mentioned circumstances, and its gist is to connect two single-mode optical fibers with a wave plate at their terminal ends. These optical fibers are optically connected to each other to form a reciprocating light guide path, the two optical fibers are wound around the outer circumference of an electric wire, and these optical fibers are connected to an optical transmitting/receiving device and a detection device to form an optical fiber. It is in the current detector used.

[Example] The present invention will be explained below based on examples.

FIG. 1 is an explanatory diagram showing a state in which a detector according to the present invention is attached to an electric wire 11. A single mode optical fiber optically connected to the terminal end via a 172 wavelength plate 8 (in this example, a 1/2 wavelength plate is used, but a 1/4 wavelength plate can also be used). 31.31 is wound around the electric wire 11. The structure of this optical fiber is such that, for example, the optical fiber 31, 31 is housed in the pipe 3 together with a protective inclusion 32, as shown in a cross-sectional view in FIG. It is natural from the nature of the present invention that plastics and non-magnetic metals are suitable materials for the pipe to be housed. A polarization maintaining optical fiber 4 is connected to one end of the optical fiber 31.
．． 4 is connected, passes through the insulating tube 12 filled with an insulating filling 17 to maintain high insulation performance, and is connected to the detection device 26. In the detection device 26, 2 is a polarizing beam splitter, 15 is a laser light source for emitted light, 61 and 62 are light receiving elements, 71 is a subtraction amplifier, 72 is a summing amplifier, and 73 is a divider.

The operation of the present invention will be explained below with reference to FIGS. 3 and 4. The polarization axes of the two polarization-maintaining optical fibers 4°4 are 45° apart from each other when coupled to the polarizing beam splitter 2.
° Installed at an angle. The arrow in the circle in FIG. 3 indicates the installation situation of the polarization axis of the polarization-maintaining optical fiber 4.

The light emitted from the laser beam [5 is divided into two optical paths by the polarizing beam splitters 2, 2, and each travels as shown by the arrow. In FIG. 3, the light reflected by the polarizing beam splitter is shown by a solid line, and the transmitted light is shown by a dotted line. FIG. 4 shows how the plane of polarization rotates while passing through the optical fiber. First, the reflected light indicated by the solid line will be explained. Since the polarization axis of the polarization-maintaining optical fiber 4 is tilted at 45 degrees as described above, the angle at the time of incidence is 45 degrees, and at the 0 part in FIG.
It has an angle of 45° as shown by ■ in the figure.

When light enters the single mode optical fiber 31 section (■), since the optical fiber itself is made of glass, it is subject to the Faraday effect, and is rotated by an angle φ in the direction of (■) in Figure 4 due to the magnetic field H generated by the electric wire. I am forced to do it. In this state 1
/2 wavelength plate 8, a phase shift of 180° occurs, and when it leaves this place (Fig. 3 -), it has rotated in the direction shown in Fig. 4 - (■).

(Due to a phase shift of 180°, it becomes the symmetrical position shown in ■.) After passing through the optical fiber further, the magnetic field H rotates by φ in the same manner as described above, while it reaches the position shown in Fig. 3 (■).
is rotating in the direction of The light that has passed through the optical fiber in this way is finally sent to the polarizing beam splitter again.
2, is reflected, and is emitted as an output light having a polarization angle of 2, and enters the light receiving element 61 shown in FIG.

Next, the behavior of the transmitted light indicated by the dotted line will be explained.

Since the polarization plane of the transmitted light of the polarizing beam splitter 2 has a phase difference of 90° with the polarization plane of the reflected light, it coincides with the polarization axis of the polarization-maintaining optical fiber, and the polarization direction at the time of incidence is The direction is shown in Figure 4 ■.

While passing through the optical fiber in this state, it is rotated by the magnetic field H, rotates by the same φ, and reaches the position shown in Figure 3 (■).
It is rotating in the direction shown in figure ■. Here, the light passes through the 1/2 wavelength plate, producing a phase difference of 18 degrees, and becomes the direction shown in FIG. While roughly passing through the optical fiber, it rotates by one φ, and at the position shown in Figure 3 ■, it becomes as shown in Figure 4 ■
The direction will be In this state, the light (2) transmitted through the polarizing beam splitter 2 is emitted as light having a polarization angle in the direction shown in FIG. The light enters the light receiving element 62 shown in FIG. The bidirectional light that has passed through the two polarization-maintaining optical fibers 4.4 and returned as described above enters the light receiving element 61.62 as orthogonal components, and is converted into an electrical signal. The sum and difference ratio of each orthogonal component is determined by a subtraction amplifier circuit 71, an addition amplifier circuit 72, and a divider 73. Since the output thus obtained is proportional to the current in the wire 11, the current can be detected using this.

What is particularly important in the configuration of the present invention is the wavelength plate provided in the middle; if this wavelength plate is not present, the Faraday effect will act in opposite directions in the round-trip optical path, and the rotations of the planes of polarization will cancel each other out. As a result, detection becomes impossible.

In the above embodiment of the present invention, a polarization-maintaining optical fiber 4 is provided between the single-mode optical fiber and the detection device, which keeps the polarization plane of light incident on the single-mode optical fiber constant. If a means for making the polarization axis of light incident on a single mode optical fiber in a fixed direction is developed separately, the polarization maintaining optical fiber can be omitted. Furthermore, the protective vibrator 3 can also be omitted if the protective coating of the optical fiber itself is strong.

[Effects of the Invention] As described above, according to the current detector of the present invention, since the current is detected by integrating the magnetic field around the electric wire, the magnetic field due to the current of other phases or other lines is detected. It is less susceptible to disturbances such as influences, there is no need to install extra optical elements such as polarizers and analyzers in the measurement section, and it can be realized as an extremely compact current detector. It is capable of accurate current detection, and the optical fiber for detection is wrapped around the electric wire, making it difficult for snow to accumulate and reducing wind noise, making it highly valued for its industrial significance. There is something to be done.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the state in which the wire current detector according to the present invention is installed, FIG. 2 is a sectional view showing an example of the structure of the optical fiber used in the present invention, and FIGS. 3 and 4 are An explanatory diagram showing the operation of the detector according to the present invention, FIG. 5 is an explanatory diagram showing an example of a conventional wire-wound type IR current detector, and FIG. 6 is an explanatory diagram showing an example of a conventional current detector using an optical fiber. It is an explanatory diagram. 2; Polarizing beam splitter 3: Pipe 4; Polarization maintaining optical fiber 5: Laser light source 8: 1/2 wavelength plate 11
: [Line 26; Detector @ 31; Single mode light)/Iba 61.6
2: Light receiving element

Claims (1)

[Claims] One or two single mode optical fibers are optically connected to each other via a wavelength plate at the terminal ends thereof to form a reciprocating light guide path, and the two optical fibers are connected to the outer periphery of the electric wire. A current detector 2 using an optical fiber is formed by winding the optical fibers around the fibers and connecting these optical fibers to an optical transmitting/receiving device and a detecting device. Current detection device 3 according to claim 1, which is formed by connecting wavefront preserving optical fibers; Claim 1, which is formed by housing two single mode optical fibers in a plastic tube or a non-magnetic metal tube. Alternatively, the current detector 4 described in Section 2, two polarizing beam splitters are installed at the ends of the optical fibers, and the light from a single light source is split into two and input into two optical fibers. Claims 1 to 3 constitute a bidirectional optical path for separating and detecting the return light of the
Current detector according to any of paragraphs