JPH09281154A - Optical fiber current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize accurate current measurement by preventing the physical shape change of a sensing fiber and reducing the influence of vibration. SOLUTION: The optical fiber current sensor is provided with a sensing fiber 1 wound on the periphery of a conductor 4 through which a current to be measured flows, a polarizer 21 which is incident to linear polarization at the incident end of the fiber 1, and an analyzer 12 for separating the emitted light from the emitting end of the fiber 1 to polarized components. An annular frame 2 of high rigidity crossing the conductor 4 is provided at the conductor 4. Cutouts 22, 32 are formed in the frame 2, the analyzer 12 and polarizer 21 are embedded, and rigidly fixed to the frame 2. The fiber 1 is wound to be brought into close contact with the frame 2, and connected to the analyzer 12 and polarizer 21 without separating from the outer periphery of the frame 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current sensor utilizing the principle that the plane of polarization of linearly polarized light propagating in an optical fiber is rotated by the Faraday effect.

[0002]

2. Description of the Related Art There is known a current measuring method utilizing the Faraday effect in which the plane of polarization of light is rotated by the action of a magnetic field.

An optical fiber current measuring device using an optical fiber in an optical path that circulates around a conductor through which a current to be measured flows is disclosed in, for example, Optics and Laser Technology, February (1).
980), pp.25, the principle composition is shown.

As shown in FIG. 11, the light from the light source 71 passes through the polarizer 72, is shaped into linearly polarized light, and then enters the sensing fiber 73 from the incident end. The linearly polarized light propagating in the sensing fiber 73 has its polarization plane rotated by the Faraday effect due to the magnetic field created by the current flowing in the conductor 74, and the light emitted from the emitting end of the sensing fiber 73 is divided into two orthogonal polarization components by the analyzer 75. The intensity of each polarization component is divided and the light receiving elements 76 and 77
Is measured and converted into a current value by the optical signal calculation device 78.

By the way, when such an optical fiber current sensor is installed on the outer periphery of the current through which the current to be measured flows, the circumference of the conductor 74 should be circulated by the sensing fiber 73 so as not to be affected by the external magnetic field. Is desirable.
In a practical current measuring device, a light guide fiber (incident fiber) 79 that guides the light from the light source 71 to the polarizer 72, and a light guide fiber (exit fiber) 80 that guides the light from the analyzer 75 to the light receiving elements 76 and 77 are also provided. Required and these are the Polarizer 7
2. It is necessary to realize a module optically connected to the analyzer 75 and the sensing fiber 73.

Therefore, the present inventors have developed a structure in which an annular frame body is installed on the outer periphery of a conductor and a sensing fiber is fixed to this frame body, and at the National Meeting of the Institute of Electrical Engineers held in 1995, Announced (Yoshida et al .: The 1995 Institute of Electrical Engineers of Japan, 28
-3a).

FIG. 12 shows a structure for fixing the sensing fiber, the polarizer and the analyzer of the optical fiber current sensor presented at this conference. In FIG.
The member indicated by 1 is a sensing fiber, and this sensing fiber 81 is arranged so as to circulate around the outer circumference of an annular frame body 82 installed on the outer circumference of a conductor (not shown).

The mounting base 83 is integrally fixed to the outer peripheral side surface of the frame body 82, and a polarizer 84 including a holder and an optical box 85 are held on the mounting base 83. The polarizer 84 is
The linearly polarized light is guided to the sensing fiber 81, and the outgoing end side thereof is the incident end 8 of the sensing fiber 81.
1a and an incident fiber 86 that guides light from the outside to the polarizer 84 on the incident end side of the polarizer 84.
Is arranged.

The optical box 85 has a built-in analyzer, prism, etc. for converting the rotation of the plane of polarization into the intensity of light, and an output fiber for extracting an optical signal containing such information to the outside. 87 is connected. However, the fixing structure of the sensing fiber 81 having such a structure has the technical problems described below.

[0010]

That is, in the fixed structure of the sensing fiber 81 having the above structure, the polarizer 84 extends in the tangential direction of the frame 82 relatively long when the holder is included, and the optical box 85 is Since the connecting portion on the output end 81b side of the sensing fiber 81 is provided near the center of its thickness, the input and output ends 81a, 81b of the sensing fiber 81 are separated from the outer periphery of the frame 82 by floating. I need to guide you.

In this case, since it is difficult to form the shape of the mounting base 83 on the peripheral end side so as to follow the curvature of the frame 82, and the strength of the sensing fiber 81 is limited,
Due to the possibility of cutting if this is placed while being pulled with a large force, the sensing fiber 81
The vicinity of the connecting portion between the mount 83 and the frame 82, and the optical box 85
It was floating up to the mount 83.

If the sensing fiber 81 has such a float, the physical shape of the sensing fiber 81 changes when an external force such as vibration is applied, which causes a problem that the measurement accuracy decreases. That is, in this type of optical fiber current sensor, the rotation of the polarization plane due to the Faraday effect is detected and the magnitude of the current is measured, but the polarization plane rotates even when the physical shape of the sensing fiber 81 changes. However, it is difficult to distinguish this rotation due to the Faraday effect and the physical shape change of the sensing fiber 81, which causes an error.

Further, since the optical box 85 containing the polarizer 84 and the analyzer is projected outward in the radial direction from the outer periphery of the frame body 82, these are compared with the vibration of the frame body 82 itself.
It was more likely to vibrate, which also caused a decrease in measurement accuracy.

Further, since the pedestal of the sensing fiber is required, the number of parts is increased, and there are many parts protruding from the frame body, and the sensor is increased in size.

The object of the present invention is to solve the above-mentioned problems of the prior art, prevent the physical shape of the sensing fiber from changing, and reduce the influence of vibration, so that highly accurate current measurement can be realized. An object is to provide a compact optical fiber current sensor.

[0016]

A first aspect of the present invention is directed to a sensing fiber wound around a conductor through which a current to be measured flows, a polarizer section for injecting linearly polarized light into an incident end of the sensing fiber, and a sensing section. In an optical fiber current sensor having an analyzer for separating light emitted from an emitting end of a fiber into polarized components, a high-rigidity annular frame body interlinking with the conductor is provided, and the frame body is provided. A notch is formed in this, and the analyzer part and the polarizer part are embedded in this and fixed to the frame body, and the sensing fiber is closely attached to the frame body and wound, and the analyzer part is not separated from the outer periphery of the frame body. And connected to the polarizer section.

Since the frame body is made of high rigidity as described above, the frame body itself is unlikely to be deformed and the physical shape of the sensing fiber wound around the frame body is unlikely to change. Also,
Since the analyzer section and the polarizer section are embedded in the notch provided in the frame and fixed to the frame, the displacement of the input / output end of the sensing fiber can be suppressed. Further, since the sensing fiber is brought into close contact with the frame, the amplitude of the fiber becomes extremely small, and the influence of vibration on the sensor output can be reduced. Further, since the sensing fiber is connected to the analyzer section or the polarizer section without being separated from the outer periphery of the frame body, the sensing fiber is not separated from the frame body even at the connection part at the input / output end.

According to a second aspect of the present invention, in the first aspect of the present invention, a sensing fiber is embedded in the vicinity of an analyzer section to which the input / output ends of the sensing fiber are connected, and the sensing fiber measured from the center of the annular frame. The angle difference between the entrance and exit ends of
It is an integral multiple of radians. Since the angle difference between the input and output ends of the sensing fiber is set to an integral multiple of 2π radians in this way, the relative displacement between the input and output ends of the sensing fiber becomes extremely small, and the measurement error becomes extremely small.

A third invention is that in the first or second invention, a groove is formed on the outer periphery of the frame, and the sensing fiber is wound along the groove. When the sensing fiber is wound along the groove formed in the frame, it can be easily attached to the frame.

In a fourth aspect of the invention, in the first to third aspects of the invention, an extra length accommodating portion for accommodating and fixing the extra length of the fiber is provided in the frame. When the extra length storage portion is provided, it is possible to prevent excessive tension from being applied to the fiber.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall external view of an optical fiber current sensor according to an embodiment of the present invention. Reference numeral 4 is a conductor through which a current to be measured flows. Reference numeral 2 denotes a ring-shaped frame body that interlinks with the conductor 4, and has a metal having high rigidity, for example, metal having high rigidity such as stainless steel or aluminum alloy, or fiber reinforced with glass fiber, ceramic fiber, carbon fiber or the like. Made of plastic etc. The sensing fiber 1 is fixed to the outer periphery of the frame body 2. Reference numeral 12 is an analyzer unit. The polarizer 21 is not shown because it is arranged in the vicinity of the analyzer 12 and the frame 2 in the axial direction. Both the analyzer section 12 and the polarizer section 21 are partially embedded in the notches 22 and 32 of the frame body 2, and in FIG. 1, only the upper portion of the analyzer section 12 projects from the outer periphery of the frame body 2.
Reference numeral 13 denotes an extra length storage unit that stores the extra length of the sensing fiber. Two output fibers 14a and 14b are connected to the analyzer section 12, and an input fiber 15 is connected to the polarizer section 21.

FIG. 2 is a sectional view showing a mounting structure of the polarizer portion 21 to the frame body 2. The polarizer unit 21 is an optical unit having a hermetically sealed structure in which the sensing fiber 1 and the incident fiber 15 are butt-connected with each other with the thin film polarizer element interposed therebetween, and the whole is housed in a thin cylindrical sleeve. The V-groove-shaped notch 22 for holding the polarizer 21 is used as the sensing fiber 1
The dimensions are selected so that the depth does not separate from the outer periphery of the frame body 2, and the polarizer portion 21 is firmly fixed by the holding plate 23 so as to be held by this. The holding plate 23 is fixed to the frame body 2 by a bolt (not shown).

FIG. 3 is a sectional view showing the mounting structure of the analyzer portion 12 to the frame body 2. The analyzer unit 12 has a rectangular parallelepiped casing structure including a birefringent crystal or the like as an analyzer element therein, and has a sensing fiber 1 and two emitting fibers 14a and 14a.
b is connected. The analyzer portion 12 is fitted into a rectangular cutout portion 32 formed in the frame body 2, and is firmly fixed to the frame body 2 by a bolt (not shown). The size of the notch 32 into which the analyzer unit 12 is fitted is determined so that the sensing fiber 1 connected to the analyzer unit 12 does not separate from the outer periphery of the frame body 2.

The polarization components separated by the analyzer element of the analyzer section 12 are received by the two emitting fibers 14a and 14b, and their light intensity signals are converted into electric signals by a light receiving element (not shown), A current value is calculated by an optical signal calculation device (not shown).

FIG. 4 shows the polarizer section 21 and the analyzer section 1 described above.
It is the figure which looked at the attachment structure of 2 to the frame body 2 from the outer peripheral surface direction of the frame body 2. The ends of the analyzer section 12 and the polarizer section 21 are arranged so that the sensing fiber 1 makes one round. That is, the incident end face of the sensing fiber 1 in the polarizer portion 21 measured from the center of the annular frame 2,
The angle difference between the exit end face of the sensing fiber 1 in the analyzer unit 12 is 2π radians. In order to make this angle difference just 2π radians, the notch 22 for housing the polarizer 21 is formed.
The notch 32 into which the analyzer portion 12 is fitted is provided with a length that allows movement in the outer peripheral direction, and the arrangement is adjusted and then fixed.

The sensing fiber 1 has a diameter of about 0.5 mm.
1 mm wide and 1 mm deep formed on the outer periphery of the frame body 2
It is wound along the groove 53, and the gap between the grooves 53 is filled with silicone resin, and the sensing fiber 1 is fixed so as not to move. Due to the mounting structure of the polarizer section 21 and the analyzer section 12, the sensing fiber 1 is fixed without being separated from the outer periphery of the frame body 2 even in the vicinity of the polarizer section 21 and the analyzer section 12.

Further, in order to arrange the polarizer portion 21 and the analyzer portion 12 as shown in FIG. 4, the groove 53 for fixing the sensing fiber 1 is provided with a step on a part of the outer periphery of the frame body 2 to form the frame body 2. The sensing fiber 1 is made to move to the step and return to a different position on the outer periphery of the frame 2 when the circuit is rotated once. The groove 53 may be formed in a spiral shape instead of providing the step.

When the analyzer portion 12 and the polarizer portion 21 are arranged so that the sensing fiber 1 makes one round as described above, the length of the sensing fiber 1 is slightly longer.
Can be longer than the perimeter of the. An extra length storage portion for the sensing fiber 1 is provided to fix the elongated portion. FIG. 5 is a conceptual diagram showing a mounting state of the extra length storage portion 13, in which the pedestal 51 is mounted on the outer peripheral surface of the frame body 2 along the groove 53 formed in the frame body 2 for accommodating the sensing fiber 1. The sensing fiber 1 placed is clamped by the upper lid 52 and fixed. This fixing is bolt 54
Done by

However, when the sensing fiber 1 has a short surplus and can be accommodated in the groove 53, the extra length accommodating portion 13 need not be provided as a matter of course.

In the above description, the case where the sensing fiber 1 goes around the frame 2 once has been described, but it may be wound two times or more. In that case, the angular difference between the input end and the output end of the sensing fiber is set to be 2π radians times the number of turns.

[Mode for Carrying Out the Invention] The mode and operation of the present invention will be described by analyzing vibration characteristics.

The rotation amount of the polarization plane direction of the linearly polarized light propagating in the optical fiber is Ross (JNRoss; Optical and Quantum Elec
The formula is given by toronics, 16 (1984) 455).
According to it, the optical fiber connects the point p and the point q in space to the curve c.
When the light travels from point p to point q, the rotation amount ΔF of the plane of polarization is the line integral from p to q along the curve c.

[Equation 1] It is represented by

Here, τ is the twist rate of the curve c, and s is the arc length.

[0035]

[Equation 2] According to the above equation, the rotation of the polarization plane of the fiber wound around the annular frame is calculated. Assuming that the outer circumference of the frame is circular, the curve formed by the fiber is

(Equation 3) Is represented by However, the parameter u was replaced with the angle θ from the center of the frame. a is the radius of the frame.

[0036]

(Equation 4) _{a (cos θ + δ x)} , a (sin θ + δ y), represented as a [delta] _Z. Δ _x , δ _y , and δ _z corresponding to the amplitude are dimensionless quantities.

When δ _z is zero, the curve of the optical fiber is a plane curve, and the twist is zero irrespective of the values of δ _x and δ _y , so that the equation (2) is always zero. . Therefore, δ _z has the greatest effect on the twist, so δ _x
= Δ _y = 0. At this time

(Equation 5) The amount of deformation caused by the vibration is a δ _z, etc., but even if the acceleration is as large as 10 G at 50 Hz, the amplitude is about 1 mm and the radius of the frame is several tens of meters.
If m is set to 100 mm, δ _x , δ _y , and δ _z are all in the order of 10 ⁻² to 10 ⁻³ .

Δ is a minute amount, and terms of squares or more can be omitted, but the derivative of δ is not always a minute amount.
However, if these are also very small quantities, the squared terms or more can be omitted, and the following simple formula can be obtained.

ΔF = δ _z (θ _in ) −δ _z (θ _out ) + δ _z ″ (θ _in ) −δ _z ″ (θ _out ) (8) θ _in and θ _out are the incident end and the output end. Is the angle. In this case, the amount of rotation of the plane of polarization is determined only by the difference between the amount of displacement at the entrance and exit of the light and the second derivative, regardless of the shape in the middle.

When small amounts of δ _x and δ _y are added to the x component and the y component, respectively, the formula of τ (θ) becomes very complicated, but under the condition that the derivative up to the third order is small. Then, it was derived by calculation that Eq. (8) holds similarly. Therefore, it has become clear that it is at least important that the relative positions of the entrance end and the exit end of the sensing fiber and their secondary differential coefficients do not fluctuate.

Considering on the basis of the above theory, there are the following three points in the process in which the vibration applied to the frame causes the change in the physical shape of the fiber. In an actual current sensor, these are combined. Can be considered

(1) The sensing fiber is released from the frame and only the sensing fiber vibrates to change the physical shape of the fiber.

(2) Even if the sensing fiber is firmly fixed to the frame body, the physical shape of the sensing fiber changes due to the vibration of the fiber mount.

(3) Even if the sensing fiber is firmly fixed to the frame and the vibration of the fiber mount is prevented, the deformation of the frame itself causes the sensing fiber in close contact with the frame to deform in the same manner as the frame. As a result, the physical shape of the sensing fiber changes.

The results of experiments conducted on the above three points will be described below.

[Experiment 1] The influence of the vibration of the sensing fiber released from the frame on the output was examined.

FIG. 6 shows the experimental method.

From the vibration generator 61 to the rigid rod-shaped vibrator 62
Is extended, and the sensing fiber 63 of the portion separated from the mounting base of the current sensor shown in FIG. 12 is placed on the tip of the rod-shaped vibrator 62, and only the sensing fiber 63 is vibrated vertically at 50 Hz, and the optical signal calculation device The output waveform of 64 was measured with the oscilloscope 65. At the same time, the vibration sensor was bonded and fixed to the rod-shaped vibrator 62, and the amplitude was monitored by the vibration measuring device 66. 67 is a light source, 14a and 14b are outgoing fibers, and 15 is an incoming fiber.

The length of the loose sensing fiber 63 is about 30 mm, and the radius of curvature is about 60 mm. The center of the sensing fiber 63 serves as the contact point between the rod-shaped vibrator 62 and the sensing fiber 63.

According to the invention of the present inventors (Japanese Patent Laid-Open No. 7-270505), the optical signal arithmetic unit 64 separates the electric signals obtained by the two light receiving elements into an AC component and a DC component, and separates each AC component. Minute and DC divided signals were obtained, and then the difference between the divided signals was measured as the final output.

FIG. 7 shows the relationship between the output and the amplitude. The output was almost proportional to the amplitude. The magnitude was 360 mV at an amplitude of 0.1 mm, which was a large value equivalent to about 130 A when converted from the current sensitivity of this current sensor.

From the above, it was found that the vibration of the sensing fiber has a serious problematic level even if the amplitude is about 0.1 mm. In other words, it was found that a structure in which the sensing fiber is free in the air should be avoided, and it is extremely important to fix the sensing fiber to the frame.

[Experiment 2] The influence of the relative displacement of the incident end and the outgoing end of the sensing fiber on the output was examined.

An experiment was conducted to examine the rotation of the plane of polarization by changing the z coordinate of the incident end of the sensing fiber by displacing the polarizer in the z direction.

As shown in FIG. 12, the polarizer 84 is mounted on the mounting base 83, and the mounting base 83 is fixed to the frame 82 by bolts 88. By changing the z-axis coordinate of the incident end of the polarizer, that is, the sensing fiber 81, by loosening the bolt 88 of the mount 83 and inserting a gap gauge under the mount 83, the change in both polarization component ratio at that time is changed. By investigating, the rotation angle of the plane of polarization was calculated. The position of the emission end, that is, the analyzer unit is fixed. In FIG. 8, the horizontal axis represents the amount of displacement at the incident end, and the vertical axis represents the rotation angle of the plane of polarization. This ratio changes linearly with respect to the z-axis coordinate, and the rotation of the polarization plane per 0.1 mm reaches 3.3 × 10 ⁻³ radian. This was a size corresponding to 130 A in the current sensor.

That is, in Equation (8), if the contribution of only the first term is observed, the amount of rotation of the plane of polarization is proportional to the z-axis coordinate of the entrance end of the fiber. It was found that it is important to suppress the displacement of the entrance end and the exit end. This experiment is an experiment in which displacement is statically applied, but in the case of vibration, vibration will appear in the output corresponding to the amplitude.

Based on this fact, in the present invention, the polarizer section and the analyzer section are embedded in the frame body and firmly fixed to the frame body, so that the input / output section is not easily displaced.

[Experiment 3] Even if the sensing fiber is in close contact with the frame, the physical shape of the sensing fiber in close contact with the frame changes due to the deformation of the frame itself. The effect on output at this time was investigated by computer simulation.

[0059]

(Equation 6) Is represented by However, since the fiber closely attached to its outer circumference is extremely thin, it can be expressed only by the angle θ from the center, and its deformation may be small, so equation (7) can be used as the expression for the rotation amount of the polarization plane. . At this time, since the frame body is annular, the displacement of the fiber can be basically described by a trigonometric function by the periodic boundary condition. In general, displacement is series-expanded by trigonometric functions, but here we have calculated the case where there is only a single mode. That is, if p is a natural number and δz = εsinpθ

(Equation 7) Is represented. Regarding the entrance end and the exit end of the sensing fiber, θ _in = 0 at the entrance end, and θ _out = 2π × ξ (ξ = 0.97 to 1.
Equation (9) was calculated by the Simpson formula in the range of 0).

The results for ε = 10 ^-3 and ε = 10 ^-2 are
9 and 10 (p is plotted for 2 and 3). From these figures, it was found that the larger ε or P, the larger the rotation angle of the plane of polarization. More importantly, when the angle difference between the entrance end and the exit end is 2π radians, the rotation amount of the polarization plane is 1 × 10 ^-12 radians or less, which is substantially zero within the error range of the numerical calculation. θ _out = 2
When π × 0.995 and the entrance end and the exit end are slightly separated from the complete circulation, a relative displacement between the entrance end and the exit end of the sensing fiber occurs. This can be interpreted as a situation similar to that described in [Experiment 2].

The rotation amount of the plane of polarization becomes large when the amplitude is large or the vibration mode is of a higher order, but the actual vibration includes various vibration modes, and among them, the one with large p is inevitable. It is difficult to suppress this. Therefore, it has been found that it is important to make the angle difference between the entrance end and the exit end as close as possible to an integral multiple of 2π radians and to prevent the fiber amplitude from increasing.

When the calculation is performed according to the equation (7) on the assumption that δ _z = ε cos θ, the same conclusion can be obtained.

In the present invention, since the sensing fiber is fixed to the frame without being separated from the outer periphery of the frame, the amplitude of the fiber, that is, ε in equation (9), becomes extremely small, and the sensing fiber is accurately framed. The relative displacement of the input and output ends of the sensing fiber is extremely small because the polarizer and the analyzer are arranged so as to circulate the body by an integral multiple of 2π radians.
The measurement error due to the cause indicated by is extremely small.

According to the above analysis and experiment, the embodiment of the present invention is not limited to what has been described so far. For example, the polarizer portion is directly fixed to the analyzer portion, and the relative displacement between the two is fixed. It is also effective to make it smaller.

It is also preferable to weld and fix the polarizer part and the analyzer part to the frame in order to integrate them with the frame.

The method of closely winding the fiber around the frame is not only by embedding it in the groove formed in the frame but also by fixing the fiber to a band-shaped metal or the like by adhesive bonding and fixing the band-shaped metal to the outer periphery of the frame. The same method can be adopted.

As the sensing fiber used here, any one having a Faraday effect such as quartz glass fiber, lead glass fiber and plastic fiber can be used. However, since the silica glass fiber has a large photoelastic constant and its birefringence easily changes due to temperature change and external stress, it is made of lead glass having a small photoelastic constant as disclosed in Japanese Patent Publication No. 3-13177. The use of the sensing fiber is advantageous in overcoming the problem of birefringence and achieving higher measurement accuracy.

As described above, the present invention is particularly useful for a photocurrent sensor used in an environment where vibration is applied, such as substation equipment, current transformers for gas insulated switches in power transmission equipment, and fault zone detectors in power transmission systems. .

The present invention is a system in which light enters from one end of the sensing fiber, light reflected at the end of the sensing fiber returns in the sensing fiber, and the polarization state of the light emitted from the sensing fiber is measured. It is also clear from the above description that it is also effective for the reflection type current sensor.

[0070]

【Example】

Example 1 The vibration error of the current sensor of the present invention was measured. FIG. 13 shows a block diagram of the experimental method. In the experiment, the current sensor was vibrated while the current to be measured was not applied, and the output of the optical signal calculation device at that time was measured.

Vibration tester F-300, manufactured by EMIC Corporation
-The current sensor 92 of the present invention is fixed to the vibration device 91 of the BM, and vibration of a frequency of 50 Hz is applied to the optical signal calculation device 9
The output of 3 is the data recorder 95 and the data analyzer 9
Measured at 6. In addition, Rion Co.
Made by piezoelectric vibration pickup PV-90B pickup 98
Was fixed with an adhesive tape, and its vibration was measured by an accelerometer 94 (VM-80, manufactured by Rion Co., Ltd.).

The light source 97 has a wavelength of 850 nm, manufactured by Anritsu Corporation, and is a super luminescent diode (SLD).
Was used.

According to the invention of the present inventors (Japanese Patent Laid-Open No. 7-270505), the optical signal calculation device 93 separates an electric signal obtained by two light receiving elements into an AC component and a DC component, and each AC This is an electronic circuit that obtains the division signal of the minute component and the direct current component and then outputs the difference between the respective division signals as the final output.

FIG. 14 shows an output waveform of the optical signal arithmetic unit when vibration of 1.0 G acceleration is applied at 50 Hz. The output vibrates following the applied vibration and its amplitude is about 10 m.
It was V. In actual current measurement, the vibration output generated by vibration is superimposed on the original AC current value to be measured, resulting in a measurement error.

The current sensitivity of this current sensor is about 0.37A.
/ MV, the measurement error of the current due to vibration was about 3.7 A in amplitude and about 2.6 A in effective value.

This error has sufficient accuracy for a current transformer such as a substation that measures an alternating current of 1000 A or more.

Comparative Example 1 The vibration error of the current sensor shown in FIG. 12 was measured by the same method as in Example 1. FIG.
Shows the output waveform of the optical signal calculation device when a vibration with an acceleration of 1.0 G is applied at 50 Hz. Output amplitude is about 300
It was mV, which was about 30 times that of Example 1. This corresponds to 100 A or more, and it must be said that the error is too large even for a current transformer such as a substation that measures an AC current of 1000 A or more.

[Embodiment 2] The frame of the current sensor of the present invention was hit with a hammer, and the output of the optical signal calculation device was measured. The vibration sensor was attached to the frame near the analyzer with an adhesive tape, and the hammering point was set on the frame approximately 10 cm from the analyzer.

FIG. 16 shows an acceleration waveform (a) monitored by an accelerometer and an output waveform (b) of the optical signal calculation device at that time. In Fig. 16 (a), the impact from the hammer is 0.02.
It starts at the second position. The maximum acceleration immediately after hitting was about 15G, but the output corresponding to this was 0.
It was about 1 V and was 40 A or less when calculated from the current sensitivity.

Comparative Example 2 The vibration characteristic of the current sensor shown in FIG. 12 was measured by the same method as in Example 2.

FIG. 17 shows an acceleration waveform (a) monitored by an accelerometer and an output waveform (b) of the optical signal calculation device at that time. The maximum acceleration immediately after impact is about 15 G, which is about the same as in Example 1, but the output waveform of the optical signal calculation device fluctuates greatly, and a peak of about 7 V appears at the maximum.
This is probably because the physical shape of the fiber was significantly deformed by the impact.

[0082]

According to the invention as set forth in claim 1, the sensing fiber is wound in close contact with the frame body and is connected to the analyzer or the polarizer without being separated from the outer periphery of the frame body, thereby performing sensing. Since the fiber is not separated from the frame, the measurement error due to the vibration of the fiber is reduced,
Highly accurate current measurement can be realized.

Further, a notch portion is formed in the frame body, and the analyzer portion and the polarizer portion are embedded and fixed in the notch portion,
Since the pedestal of the sensing fiber is unnecessary, the number of parts is reduced, and the sensor can be downsized because there are few parts protruding from the frame.

According to the second aspect of the invention, the angle difference between the entrance end and the exit end of the sensing fiber measured from the center of the annular frame is set to an integral multiple of 2π radians, and the sensing fiber is completely circulated. In this case, in addition to reducing the measurement error due to vibration, it is possible to eliminate the influence of the external magnetic field and the external current, and it is possible to measure the current with higher accuracy.

According to the third aspect of the invention, the groove is formed in the frame body, and the sensing fiber is wound in close contact with the frame body along the groove. The sensing fiber can be wound more closely on the frame more easily than in the case where the band-shaped metal or the like is fixed by adhesion and fixed to the outer periphery of the frame.

When the extra length storage portion for the sensing fiber is provided as in the fourth aspect of the invention, it is possible to prevent excessive tension from being applied to the sensing fiber.
Accidents such as fiber cutting and damage can be effectively prevented.

[Brief description of drawings]

FIG. 1 is an overall external view of a current sensor according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an attachment structure of a polarizer portion to a frame body according to the present embodiment.

FIG. 3 is a cross-sectional view showing a structure for attaching an analyzer unit to a frame body according to the present embodiment.

FIG. 4 is a view of a structure of attaching the polarizer section and the analyzer section to the frame body according to the present embodiment, as viewed from the outer peripheral surface direction of the frame body.

FIG. 5 is a conceptual diagram showing a mounting state of an extra length storage section according to the present embodiment.

FIG. 6 is an explanatory diagram showing an experimental method for examining the influence of the vibration of the sensing fiber released from the frame on the output.

7 is a diagram showing the relationship of the output to the amplitude of the fiber of the output of the optical signal calculation device in FIG.

FIG. 8 is a diagram showing a rotation angle of a plane of polarization with respect to a displacement amount of an incident end of a sensing fiber.

FIG. 9 is a diagram showing a rotation angle of a polarization plane with respect to an angle difference between an incident end and an emitting end of a sensing fiber when ε = 10 ⁻³ .

FIG. 10 is a diagram showing a rotation angle of a polarization plane with respect to an angle difference between an entrance end and an exit end of a sensing fiber when ε = 10 ⁻² .

FIG. 11 is a principle configuration diagram of a conventional optical fiber current sensor.

12A and 12B are views showing a structure for fixing a sensing fiber, a polarizer and an analyzer of a conventional optical fiber current sensor, wherein FIG. 12A is a front view and FIG. 12B is a bottom view.

FIG. 13 is an explanatory diagram showing an experimental method for measuring a vibration error of a current sensor.

14 is an acceleration of 1.0 at 50 Hz in Example 1. FIG.
It is a figure which shows the output waveform of an optical signal arithmetic unit when G vibration is added.

15 is an acceleration of 1.0 at 50 Hz in Comparative Example 1. FIG.
The output waveform of an optical signal arithmetic unit when G vibration is applied is shown.

16A and 16B show striking characteristics of the current sensor in Example 2, where FIG. 16A is an acceleration waveform monitored by an accelerometer, and FIG.
FIG. 4 is an output waveform diagram of the optical signal arithmetic unit at that time.

FIG. 17 shows a striking characteristic of a current sensor in Comparative Example 2, (a) is an acceleration waveform monitored by an accelerometer, and (b) is a graph.
FIG. 4 is a diagram showing an output waveform of the optical signal arithmetic unit at that time.

[Explanation of symbols]

 1 Optical Fiber Sensor 2 Frame 3 Extra Length 4 Conductor 12 Analyzer 15 Incident Fiber 16 Output Fiber 21 Polarizer 22 Notch 23 Notch

Claims (4)

[Claims] 1. A sensing fiber wound around a conductor through which an electric current to be measured flows, a polarizer section for injecting linearly polarized light into an incident end of the sensing fiber, and an outgoing light from an outgoing end of the sensing fiber. In an optical fiber current sensor having an analyzer section for separating into wave components, a high-rigidity annular frame body interlinking with the conductor is provided on the conductor, and a notch section is formed in the frame body. The analyzer part and the polarizer part are embedded in a part and fixed to a frame body, and the sensing fiber is closely wound around the frame body, and the analyzer part is kept without being separated from the outer periphery of the frame body. An optical fiber current sensor connected to the above-mentioned polarizer. 2. An analyzer part and a polarizer part, to which the entrance and exit ends of the sensing fiber are connected, are buried in the vicinity, and the entrance end and the exit end of the sensing fiber are measured from the center of the annular frame. The optical fiber current sensor according to claim 1, wherein the angle difference between them is an integral multiple of 2π radians. 3. The optical fiber current sensor according to claim 1, wherein a groove is formed on the outer periphery of the frame body, and the sensing fiber is wound along the groove. 4. An extra length accommodating portion for accommodating and fixing an extra length of the fiber is provided in the frame body.
The optical fiber current sensor according to any one of 1.