JPH0641960B2 - Current detector using optical fiber - Google Patents

Description

The present invention relates to an improvement of a current detector using an optical fiber.

[Prior Art] Conventionally, as a detector for detecting a current flowing through a transmission line,
Winding type current transformers (CT) have been widely used as shown in FIG. This is composed of a primary winding 13, an iron core 14, a secondary winding 15, a measuring terminal 16, an insulating filler 17, and a current transformer 10 which are protected by an insulator 12.
However, as the transmission voltage became higher, this current transformer also became larger and the price was higher.

In recent years, the practical application of optical fibers has progressed rapidly, and a current detector as shown in FIG. 6 utilizing the electro-optical effect of magnetism, that is, the Faraday effect has been proposed and put into practical use. That is, the Faraday element 25 is provided in the vicinity of the magnetic field H generated by the current flowing through the electric wire 11, the light is emitted and guided to the optical fiber 21 connected to the detector 26, and the emitted light is emitted through the polarizer 23. The Faraday element 25 is made to enter light, and the light whose polarization plane is rotated by the magnetic field H in the Faraday element 25 is made to enter the optical fiber 22 through the analyzer 24, and the rotation angle of the light is detected to detect the current. The current value is to be detected from the rotation angle that is proportional to the intensity.

[Problems to be Solved by the Invention] The current detector using the above optical fiber is more compact and more economical than the conventional current transformer type shown in FIG. 5, but the following problems still remain. There is. That is, firstly, it is affected by a disturbance such as the influence of a magnetic field due to another phase current, and secondly, the accuracy of the distance from the transmission line to the installation position directly affects the detection accuracy. In addition, extra optical components such as a polarizer and an analyzer are required before and after the Faraday element.

In addition, by utilizing the Faraday effect of the optical fiber itself without using a Faraday element, etc., a part of one optical fiber loop is arranged in a coil around the power transmission line, and the bidirectional propagation light in the optical fiber loop is A current detector for detecting the phase difference between the two or detecting the rotation angle of the linearly polarized light has also been proposed (Japanese Patent Laid-Open No. Sho 61-206).
No. 56-55864, No. 57-190483. ) However, 1
Since the two optical fibers must be arranged in a coil around the power transmission line and both ends of the optical fibers must be optically coupled to form a loop, the installation work is cumbersome and impractical.

Further, there is a drawback that an error occurs in detecting the rotation angle due to a change in light intensity of the light source or a change in loss. Therefore, there has been a strong demand for the appearance of an optical current detector having the above-mentioned problems, accuracy higher than that of a conventional wire-wound detector, and 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 provide a light receiving element and a light source for the light emitting element. Polarization beamsplitters and polarization axes of 45 ° with respect to each other
Two polarization-maintaining optical fibers that are tilted and connected to each other, connected to the polarization-maintaining optical fiber, connected through a 1/2 corrugated plate at the terminal end, and housed in a plastic tube or non-magnetic metal tube Are integrated in the longitudinal direction, two single-mode optical fibers wound around the outer circumference of the electric wire to be measured, and the return light from the polarization-maintaining optical fiber are the two polarized beams. It is composed of two light receiving elements that receive light via a splitter and a detection device that subtracts, adds and divides the outputs of the light receiving elements, and divides the light from the light emitting element into two by two polarization beam splitters. At the same time, the polarization plane is rotated by the magnetic field of the electric wire to be measured in the single-mode optical fiber by bidirectionally propagating to the two single-mode optical fibers through the polarization-maintaining optical fiber. Rotation of Light is received by two light-receiving elements via a polarization-maintaining optical fiber and two polarization beam splitters, and the current value of the measured wire is obtained from the rotation of the polarization plane by dividing the difference and the sum of the received light output. A current detector using an optical fiber characterized by being configured as described above.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory view showing a state in which the detector according to the present invention is attached to the electric wire 11. Has a half-wave plate 8 at the end,
The two single mode optical fibers 31, 31 optically connected via the / 2 wave plate 8 are integrated in the longitudinal direction to form a reciprocal light guide path, which is spirally formed on the electric wire 11. Wrapped around. The structure of the two integrated optical fibers is, for example, as shown in the sectional view of FIG.
The structure is stored inside. It is natural from the nature of the present invention that plastic and non-magnetic metal are suitable as the material of the pipe to be stored. The polarization-maintaining optical fibers 4 and 4 are connected to one ends of the optical fibers 31 and 31 and are passed through the porcelain tube 12 filled with the insulating filler 17 to maintain high insulation performance, and are connected to the detection device 26. To be done.
In the detection device 26, 2 is a polarization beam splitter,
5 is a laser light source for emitted light, 61 and 62 are light receiving elements,
71 is a subtracting amplifier, 72 is an adding amplifier, and 73 is a divider.

The operation of the present invention will be described below with reference to FIGS. The polarization axes of the two polarization-maintaining single-mode fibers 4 and 4 are 45 degrees relative to each other when coupled to the polarization beam splitter 2.
It is installed at an angle. The arrow in the circle in FIG. 3 shows the installation state of the polarization axis of the polarization-maintaining optical fiber 4.

The light emitted from the laser light source 5 is split into two optical paths in the polarization beam splitters 2 and 2 and travels as shown by arrows. In FIG. 3, the light reflected by the polarization 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 during passage through the optical fiber. First, the reflected light shown with a solid line will be described. Since the polarization axis of the polarization-maintaining single-mode fiber 4 is tilted by 45 ° as described above, the incident angle is 45 °, and the angle in FIG.
It has an angle of 45 ° as shown. When the light enters the single mode optical fiber 31 portion, the optical fiber itself is glass, so that it receives the Faraday effect by itself, and the magnetic field H generated from the electric wire causes an angle φ in the direction of FIG.
Only can be rotated. In this state, it enters the half-wave plate 8 and causes a phase shift of 180 °, and when it leaves this (Fig. 3), it rotates in the direction of Fig. 4. (180
(It becomes a symmetrical position due to the phase shift of °). Here, while passing through the optical fiber, the magnetic field H
As described above, a rotation of -φ occurs in the same manner as described above, and the rotation is in the direction of FIG. The light thus passing through the optical fiber finally enters the polarization beam splitter 2 again and is reflected (the longitudinal component L of the emitted light having a polarization angle).
₁ ) and is incident on the light receiving element 61 of FIG.

Next, the behavior of the transmitted light shown by the dotted line will be described.
The polarization plane of the transmitted light of the polarization beam splitter 2 has a polarization plane of the reflected light and a polarization plane of 90 ° (as a property of the polarization beam splitter, 90 ° between the reflected light and the transmitted light).
Therefore, if the reflected light is the vertical axis in FIG. 4, the transmitted light corresponds to the horizontal axis in FIG. 4).
The polarization direction upon incidence coincides with the polarization axis of the polarization-maintaining optical fiber and is the direction shown in FIG. While passing through the optical fiber in this state, it is rotated by the magnetic field H, is rotated by the same φ, and is rotated in the direction of FIG. 4 at the position of FIG. Here, a phase difference of 180 ° is generated by passing through the half-wave plate, and the direction is as shown in FIG. 4, which is the axially symmetric direction. Further, while passing through the inside of the optical fiber, it is rotated by -φ, and at the position of FIG. 3, it becomes the direction of FIG. In this state, the light transmitted through the polarization beam splitter 2 is emitted as light having a polarization angle in the direction of FIG. 4, which is a direction of 45 ° with respect to the polarization angle of the emitted light of the reflected light, and is received in FIG. It is incident on the element 62.

The bidirectional light returning after passing through the two polarization-maintaining single-mode optical fibers 4 and 4 as described above is received by the light receiving elements 61 and 62.
Incident on the input signal and converted into an electric signal, and the ratio of each sum and difference is obtained by the subtraction amplification circuit 71, the addition amplification circuit 72, and the divider 73. That is, the size of the emitted light and L
₁ and L ₂ are as follows: L ₁ = K · sin (45 ° −2φ) ... (1) L ₂ = K · cos (45 ° −2φ) (2) Here, K is a constant including light intensity and loss. Considering this emitted light as the power of light, L ₁ ′ = K ′ · sin ² (45 ° −2φ) ... (3) L ₂ ′ = K ′ · cos ² (45 ° −2φ) ... (4) Becomes

Applying Eq. (3) and Eq. (4) to the theorem of trigonometric functions, L ₁ ′ = K ″ (1-sin4φ) ... (5) L ₂ ′ = K ″ (1 + sin 4φ) ... (6)

Here, when the values of the outputs L ₁ ′ and L ₂ ′ are summed by the adder circuit 72, the difference is taken by the subtraction circuit 71, and divided by the divider 73, And the constant K ″ is omitted.

When φ is small, −sin4φ≈4φ∝H∝ current value.

The output thus obtained is proportional to the current of the electric wire 11, so that the current can be detected.

As is clear from the above formula (7), the constant K is deleted by dividing the two outputs, so that the light intensity of the light source or the change of the transmission loss is not affected and is highly accurate. The rotation angle can be detected. In the configuration of the present invention, what is particularly important is the half-wave plate provided in the middle, and without this half-wave plate, the Faraday effect acts in the opposite direction in the reciprocating optical path to rotate the polarization plane. As a result, they cancel each other out, making detection impossible.

In the above-described embodiment of the present invention, the polarization-maintaining optical fiber 4 is provided between the single-mode optical fiber and the detection device, but this makes the polarization plane of the light incident on the single-mode optical fiber constant. This is because it is fake.

[Advantages of the Invention] As described above, according to the current detector of the present invention, since the current is detected in the form of circular integration around the wire, the influence of the magnetic field due to the current of the other phase or the other line, etc. It is less susceptible to external disturbances, does not require extra optical elements such as polarizers and analyzers in the measurement section, and can be realized as a very small current detector. Since it is integrated, it is extremely easy to install on the electric wire, and it is possible to detect current with high accuracy with such a simple structure, and the optical fiber for detection is wrapped around the electric wire. Its significance on the industry, such as the difficulty of snow accretion and the effect of low wind noise, should be highly evaluated.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a state in which an electric wire current detector according to the present invention is attached, FIG. 2 is a sectional view showing an embodiment of the structure of an optical fiber used in the present invention, and FIGS. 3 and 4 are FIG. 5 is an explanatory view showing the operation of the detector according to the present invention, FIG. 5 is an explanatory view showing an example of a conventional wire-wound type current detector, and FIG. 6 is an example of a conventional current detector using an optical fiber. FIG. 2: polarization beam splitter, 3: pipe, 4: polarization-maintaining optical fiber, 5: laser light source, 8: 1/2 wavelength plate, 11: electric wire, 26: detection device, 31: single-mode optical fiber, 61, 62: Light receiving element.

Claims (1)

[Claims] 1. A light emitting element, two polarization beam splitters for dividing the light source of the light emitting element into two, and two polarization plane preserving light connected to the beam splitters with their polarization axes inclined at 45 °. The fiber and the polarization-maintaining optical fiber are connected to each other through a half-wave plate at the end, and they are housed in a plastic tube or a non-magnetic metal tube and integrated in the longitudinal direction to be measured. Two single mode optical fibers wound around the outer circumference of the target electric wire, and two light receiving elements for receiving the return light from the polarization-maintaining optical fiber via the two polarization beam splitters. ,
It comprises a detection device for subtracting, adding and dividing the output of the light receiving element, and splits the light from the light emitting element into two by two polarization beam splitters, and through the polarization maintaining optical fiber, By bidirectionally propagating in the single-mode optical fiber, the plane of polarization is rotated by the magnetic field of the measured wire in the single-mode optical fiber, and the rotation of the plane of polarization is maintained by the polarization-maintaining optical fiber and the two polarizations. Light is received by two light receiving elements via a beam splitter, and the current value of the measured electric wire is obtained from the rotation of the polarization plane by dividing the difference and the sum of the received light output. Current detector using optical fiber.