JPS6165168A - Optecal fiber type current sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fiber optic current sensor for protection purposes.

[Conventional technology]

Optical fiber current sensors that utilize the Faraday effect are known. In the well-known Faraday effect, the plane of polarization of a linearly polarized ray of light in a particular light-guiding material changes from an axis extending parallel to the ray under the influence of a magnetic field extending along the ray. rotated around. The angle of rotation of the plane of polarization is approximately proportional to the strength of the magnetic field.

Optical switches for optical fiber communication lines are known which require little optical energy. This light switch is 1
It includes one movable optical fiber, two fixed optical fibers, one coil, and a pair of permanent magnets. The movable optical fiber is provided with a magnetic alloy layer within the coil. Furthermore, the coil is placed within the magnetic field of the permanent magnet. The movable optical fiber and one fixed optical fiber are axially arranged. The axial magnetization of the magnetic alloy layer can be reversed by a coil. In this way, the movable optical fiber switches between the two fixed optical fibers (Magazine Electronics (E
electronics) J, February 9, 1984, p. 62).

[Problem that the invention seeks to solve]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical fiber current sensor for protection purposes that is simple in structure and has sufficient sensitivity and potential insulation ability. Furthermore, it is an object of the present invention to provide a fiber optic current sensor which allows the distance between the sensor and the evaluation electronics to be selected almost arbitrarily and which is capable of evaluating currents with a bandwidth of several k tlz. It is to provide.

[Means for solving problems]

This object is achieved according to the invention by an optical fiber current sensor according to claim 1. One end of at least one optical fiber is provided with a magnetic layer and is placed in the magnetic field of the current-carrying conductor, thereby exerting a force on this end. This force causes a shift in the ray path of the light exiting this end of the optical fiber. This deviation is a measure of the current Φ flowing through the conductor. at least 1
The use of one optical fiber and one optical device provides potential isolation for almost any potential difference. One advantageous application of fiber optic current sensors is therefore the current measurement of high voltage installations for protection purposes. The fiber length and the mass of the magnetic layer at the end of the optical fiber determine the bandwidth of this fiber optic current sensor.

In one advantageous embodiment of the fiber optic current sensor,
The ends of the first and second optical fibers are arranged axially opposite and parallel to the axis of symmetry of the current-carrying conductor and are each provided with one permanent magnet layer. A light emitting diode LED is provided as a light source. In this arrangement, the respective forces acting on the magnetic ends and the resulting rotational torques on the holding device are equal and opposite in direction. The effective magnetic field for the magnetic end of the optical fiber is, for example, uniform.

Another advantageous implementation! In the third type, one reflective surface is provided opposite the end of the optical fiber provided with the magnetic layer. The percentage of light that is reflected back into the optical fiber is one measure of the ray path deviation of the light exiting the optical fiber. Since the branching into the light-transmitting and light-receiving optical fibers takes place outside the sensor element, the geometric dimensions of the fiber-optic current sensor can be significantly reduced.

In one particularly advantageous embodiment, the reflective surface is formed by one of the end faces of the second optical fiber arranged in the holding device. Because it affects the characteristic curve, that is, the relationship between optical fiber deflection and the ratio of transmitted light amount to reflected light amount,
The optical fiber end face or reflective surface may be curved.

In a further advantageous embodiment, the current sensor is arranged inside a current-carrying conductor that is partially designed as a U-shaped loop or coil. The magnetic field is thereby strengthened and equalized at the location of the sensor element, and the sensitivity of the device is increased.

〔Example〕

The invention will be explained in more detail below by means of embodiments shown in the drawings.

According to FIG. 1, one end 48 of the optical fiber 46 has a magnetic Ji
i20 and is placed in the magnetic field of the current-carrying conductor 26. The force acting on the magnetic layer 20 from the magnetic field causes the optical fiber 46 stretched within the holding device 80 to
The free end of 4 days is swung from its rest position in the case of no current. The optical ray path deviation α of the light exiting the optical fiber 46 is measured by the optical device 90, and this deviation is one measure of the current I flowing through the conductor 26.

In the embodiment according to FIG. 2, the fiber optic current sensor has one
It includes two light sources 2. two optical fibers 4 and 6. one photodetector 8 and evaluation electronics 10. One end 12 of the first optical fiber 4 is connected to a light source 2, and one end 14 of the second optical fiber 6 is connected to a photodetector 8, which may for example be a photodiode. Both other ends 16 and 18
are magnetic layers, preferably permanent magnet layers 20 or 2, respectively.
2 is provided. The ends 16 and 18, which are provided with permanent magnetic layers 20 and 22, are each placed in close proximity to the current-carrying conductor 26 by a holding device 24. Permanent magnetic layers 20 and 22 are located at ends 16 and 1, respectively.
8 with an axial magnetization direction. The ends 16 and 18 are arranged axially opposite and parallel to the axis of symmetry 28 of the conductor 26 such that maximum transmission of light 42 occurs, for example in the currentless conductor 26. The light source 2 is an incandescent lamp, preferably a laser,
In particular, light emitting diodes LEDs are provided. When a current I flows through conductor 26, a force acts on m16 and 18 of optical fibers 4 and 6, respectively, as a result of the resulting magnetic field. This field is uniform for ends 16 and 18. That is, the forces acting on ends 16 and 18 and the resulting rotational torques are equal.

The forces acting cause the ends 16 and 1 to be displaced in the opposite direction relative to their rest position. That is, the direction of motion at end 16 is out of the page, and the direction of motion at end 18 is into the page. This weakens the transmission of light. The transmitted light is detected by a photodetector 8. Evaluation electronic circuit 10 connected after the photodetector
(which may be a microcomputer, for example) associates the detected amount of light with one current value within a predetermined current range of, for example, 10 times the rated current. If the value of the current ■ flowing through the conductor 26 at the time of a short circuit is, for example, 100 times the rated current, the evaluation electronic circuit 10
The value of the current I that actually flows is determined from the slope of the change in the amount of transmitted light from 0% to 0%.

In another embodiment according to FIG. 3, the ends 16 and 18 of the optical fibers 4 and 6, which are provided with permanent magnet layers 20 and 22 and are arranged axially opposite each other, are aligned with the axis of symmetry 28 of the current-carrying conductor 26. is placed perpendicular to the The magnetic field lines caused by the current flowing through the conductor 26 are indicated by the dashed circle 30. The ends 16 and 18 of the optical fibers 4 and 6 are acted upon by forces F and F2 of different magnitude and opposite direction. The different magnitudes of the forces Fl and F2 are indicated in the drawing by different lengths of the arrows.The directions of action of the forces Fl and F2 are such that the magnetic field due to the current ■ is applied to the magnetic dipole at the end 16 or 18 of the optical fiber 4 or 6. It is the result of the combination of the forces exerted. The end 16 closer to the axis of symmetry 28 swings significantly from its rest position as a result of the large forces. Therefore, the permanent magnet layer 20 is only attached to the end 16 of the optical fiber 4 that is closer to the current-carrying conductor 2G.
It is advantageous to provide The different forces are applied to the current-carrying conductor 26
This is caused by the forces being unequal with respect to the ends 16 and 1.

This configuration provides a fiber-optic current sensor that can be placed in the vicinity of a current-carrying conductor 26, for example a high-voltage conductor, and that can be used with the same construction for different current ranges. The current of il with no potential
l [IJ can be determined, and the distance between the sensor and the evaluation electronic circuit 10 can be selected almost arbitrarily, for example from several meters to lkm. With this simple configuration of the current sensor, it is possible to measure both alternating current and, in some cases, direct current. In the case of alternating current, there is no need to place high requirements on the light source 2, such as stability or light intensity. This is because there is one reference point when the magnetic field passes through the zero point. This reference point makes it possible to compensate for the influence of environmental conditions on the transmission line and the influence of aging of the light source and photodetector in a simple manner.

In the embodiment according to FIG. 4, the fiber optic current sensor has one
2 light sources 2. 1 photodetector 8. 1 optical fiber 40
．． It includes one evaluation electronics lO and one fiber coupler 60. Light source 2 and photodetector 8 are connected to fiber coupler 60 by optical fibers 62 or 64, respectively.
is connected to. The fiber coupler 60 connects the optical fiber 4
It is connected to one end 42 of 0. The optical fiber 40 is provided with a magnetic layer 20 at the other end 44 . The end 44 of the optical fiber 40 is arranged, for example, in the holding device 24 parallel to the axis of symmetry 28 of the conductor 26. A reflective surface 54 opposite the end 44 is provided in the holding device 24 such that, for example, when no current is flowing through the conductor 26, light exiting the optical fiber 40 at the end 44 is incident on the reflective surface 54 and at least partially It is arranged to be reflected back into the optical fiber 40. When a current (1) is flowing through the conductor 26, the force acting on the magnetic layer 20 causes the m44 of the optical fiber 40 to be moved one arm from a position parallel to the axis of symmetry 28. As a result, the proportion of the light that is reflected back into the 1-Iha 40 is reduced. The branching into the optical fiber halo 2 for transmitting the light and the optical fiber halo 4 for receiving the light is performed by a single fiber coupler 60 outside the sensor element. In this way, it is sufficient to lead a single optical fiber 40 to the current-carrying conductor 26 to be monitored, so that the geometric dimensions of the fiber-optic current sensor are
Compared to the embodiment according to FIGS. and FIG. 3, further reductions can be made. That is, in these embodiments, at least one of the two optical fibers 4 or 6 must be curved so that it can be led to the control electronics in common with the other optical fiber halo or 4. The smallest possible bending radius of the optical fiber limits the miniaturization of the sensor.

The magnetic layer 20 is made of, for example, a permanent magnetic material.

However, in applications where the current flowing through the conductor is large and therefore does not place very high demands on the sensitivity of the sensor,
It is also advantageous to provide the end 44 of the optical fiber 40 with a soft magnetic material. The use of soft magnetic materials has the advantage that, in addition to ease of processing, the accuracy requirements during the mechanical assembly of the sensor are reduced. This is because the orientation of the end 44 of the optical fiber 40 is independent of the direction of current flow in the conductor 26 when using the soft magnetic layer 20, and therefore, when moving the optical fiber, the magnetic field in the alternating current is transmitted. This is because it is always given as the maximum or minimum when passing the zero point of . Increased sensitivity of the sensor is achieved by having the reflective surface 54 and/or the optical fiber end face 442 have appropriate curvature.

In the embodiment according to FIG. 5, one optical fiber 56 is arranged in the holding device 24 opposite the end 44 of the optical fiber 40. In the embodiment according to FIG. Both end faces 562 and 5 of the optical fiber 56
One of 64 is provided with one reflective layer. This results in a simple manner in which a reflection area is not larger than the area of the exit aperture 442 of the optical fiber 40 and thus also increases the sensitivity of the entire sensor compared to the sensor according to FIG. By suitably curving at least one of the end faces 562, 564 and 442, the characteristic curve can be influenced as desired.

In the embodiment according to FIG. 6, the current-carrying conductor 26 to be monitored is U
It has the shape of a letter loop. A fiber optic current sensor is mounted between the substantially parallel legs 262 and 264 of the current-carrying conductor 26, and the end 44 of the optical fiber 40 and the optical fiber 56, which is provided with a reflective end face 564, are also connected to the legs 262 and 264.
64 and is arranged to extend substantially parallel to 64.

Thereby, the strength of the magnetic field prevailing at the location of the magnetic layer 20 is increased and the spatial gradient of the magnetic field is reduced compared to sensors with straight conductors.

A portion of the current-carrying conductor 26 is 1 as in the embodiment according to FIG.
The optical fiber sensor is connected to the end 44 of the optical fiber 40 inside the coil 266.
The sensitivity of the sensor can be further increased by arranging the coils 266 to extend substantially perpendicular to the magnetic field inside the coil 266.

[Brief explanation of the drawing]

1 is a schematic diagram of one embodiment of the invention, FIGS. 2 and 3 are schematic diagrams of an advantageous embodiment of the invention, and FIGS. 4 and 5 are other advantageous embodiments of the invention. Example Schematic Diagrams FIGS. 6 and 7 are schematic diagrams of particularly sensitive embodiments of fiber optic current sensors according to the invention. 2... Light source, 4.6... Optical fiber, 8... Photodetector, 10... Electronic circuit for evaluation, 12-1 day... End of optical fiber, 20.22... Magnetic layer, 24... Holding device, 26... Current-carrying conductor, 40... Optical fiber,
44... End of optical fiber, 54... Reflective surface, 56...
...Optical fiber, 60...Fiber coupler, 62.6
4... Optical fiber, 80... Holding device, 262.2
64... Leg portion, 442.562.564... End face of optical fiber. FIo 1 FIG 4 FIo 5

Claims (1)

[Claims] 1) At least one optical fiber (46) is provided, one end (48) of which is provided with a magnetic layer (20) and placed within the magnetic field of the current-carrying conductor (26). and
Further, an optical device (9
0) is provided. 2) Two optical fibers (4, 6) are provided, the first optical fiber (4) having a light source (2) at its end (12);
A second optical fiber (6) is provided at one end (14) with a photodetector (8) to which is later connected an evaluation electronic circuit (10), and at least one of the other ends (16 or 18) is provided with a permanent magnet layer (20 or 22), the ends (16, 18) of which are arranged axially opposite each other in the magnetic field of the current-carrying conductor (26), and a retaining device (24) ) The optical fiber type current sensor according to claim 1, wherein the optical fiber type current sensor is provided with: 3) The end (1) provided with a permanent magnet layer (20, 22)
6, 18) are arranged parallel to the symmetry axis (28) of the current-carrying conductor (26). 4) The end (1) provided with a permanent magnet layer (20, 22)
6, 18) are arranged perpendicularly to the axis of symmetry (28) of the current-carrying conductor (26). 5) One optical fiber (40) is provided, one end (42) of which is connected to a fiber coupler (60), which connects the light source (2) with the optical fiber (62, 64). The other end (44) is provided with a magnetic layer (20) and is connected to a current-carrying conductor (26). ) is positioned by the holding device (24) in the magnetic field of the reflective surface (
54) is located in the optical fiber type current sensor according to claim 1. 6) The reflective surface is one of the end faces (562 or 5) of the second optical fiber (56) arranged in the holding device (24).
64) The optical fiber type current sensor according to claim 5, characterized in that it is formed by: 7) End face (442) of the end (44) of the optical fiber (40)
The optical fiber type current sensor according to claim 5, characterized in that the reflecting surface (54) is curved. 8) End surface (442) of the end (44) of the optical fiber (40)
7. The optical fiber type current sensor according to claim 6, wherein one of the end faces (562 or 564) of the second optical fiber (56) is curved. 9) a portion of the current-carrying conductor (26) has a U-shaped loop with at least substantially parallel legs (262 and 264), and the end (44) of the optical fiber (40) has a U-shaped loop with legs (262 and 264) that are at least substantially parallel; The optical fiber type current sensor according to any one of claims 5 to 8, wherein the optical fiber current sensor is arranged parallel to (262 and 264). 10) A portion of the current-carrying conductor (26) is a coil (266), and the end (44) of the optical fiber (40) is arranged inside the coil (266) perpendicular to the magnetic field. An optical fiber type current sensor according to any one of claims 5 to 8. 11) The optical fiber type current sensor according to claim 2 or 5, characterized in that a microcomputer is provided as the evaluation electronic circuit (10).