JP2000266787A - Optical current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a current sensor stable against a temperature change and influenced little by a noise generated on a circuit, without requiring a temperature control mechanism. SOLUTION: This sensor is so composed that a sensor fiber 2 is fixed on a position encircling a conductor 1, and that linear polarized light is propagated, and that light is branched into orthogonal two components by propagating linear polarized light, and that a current is detected by intensities thereof. In this case, a curvature of the sensor fiber 2 and material of a fixing frame 3 are selected, so that the ratio between an alternating current component having the intensity of either of the orthogonal two components and a direct current component is not changed relative to a temperature. The ratio between an alternating current component of the orthogonal two components and a direct current component is operated, and the sum or the difference thereof is corrected from the time-average value of the ratios between the alternating current component and the direct current component, to thereby detect the current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of measuring a magnitude of a current flowing through a conductor from a Faraday rotation angle of light propagating in the sensor fiber by circulating a sensor fiber around a conductor through which a current to be measured flows. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocurrent sensor, and more particularly to a photocurrent sensor that stably detects current with respect to environmental temperature changes.

[0002]

2. Description of the Related Art A photocurrent sensor utilizing a fact that a sensor fiber causing a Faraday effect is wound around a conductor through which a current to be measured flows and the Faraday rotation angle of light propagated through the sensor fiber is proportional to the current to be measured. Is disclosed in
270505, JP-A-35994, JP-A-8-11
0357.

[0003] In these known examples, light is branched into two orthogonal components, and a current is detected from the light intensity.
This component is called linearly polarized light (P-polarized light, P component) whose electric field vector oscillates in the plane of incidence and linearly polarized light (S-polarized light, S component) whose electric field vector oscillates perpendicular to the plane of incidence.

[0004]

Generally, in the above-described photocurrent sensor, when the temperature changes, the measurement accuracy decreases due to the following two factors. When mounting a photocurrent sensor on power equipment, the sensor fiber is fixed to the mounting frame, so if the mounting frame is thermally deformed due to temperature changes, the curvature or twist of the sensor fiber wound around the outside of the conductor will change. appear. The change in the curvature or the twist of the sensor fiber acts in the same manner as the Faraday effect, causing a change in the rotation angle of the polarization plane, resulting in a measurement current detection error.

[0005] Hereinafter, the effect when the sensor fiber is bent will be described with reference to FIG. When the direction of the current to be measured is Z and the sensor fiber 2 is arranged in a circle on the X and Y planes as indicated by the dotted line, no change in the polarization angle due to bending occurs.

However, the sensor fiber 2 shown by a solid line
Has an angle γ with respect to the X and Y planes, the polarization angle changes. For this reason, in Japanese Patent Application Laid-Open No. 8-35994, the change in the polarization angle due to the bending of the sensor fiber is canceled out by reciprocating propagation in the sensor fiber, or in Japanese Patent Application Laid-Open No. 7-270505,
The influence of bending is reduced by branching into components, P-polarized light and S-polarized light, and calculating the average value of both.

On the other hand, the Verdet constant V representing the sensitivity of the sensor fiber to the current changes with a change in temperature and causes an error. In JP-A-8-35994, the sensor fiber is surrounded by a heat insulating material to suppress the temperature change of the sensor fiber itself. In JP-A-8-110357, a cooling device is provided to control the temperature of the sensor fiber to be constant. However, it is difficult to completely suppress the temperature change even if a heat insulating material is used, and if a cooling device is used, the structure of the sensor unit may be complicated.

Accordingly, an object of the present invention is to suppress measurement errors due to temperature changes as described above with simpler means.

[0009]

In order to achieve the above object, the present invention provides a conductor through which an alternating current to be measured flows, a sensor fiber having a Faraday effect and installed around the conductor, and An optical current sensor comprising: means for causing light to enter the sensor fiber; and means for detecting the magnitude of the current to be measured from the light propagated through the sensor fiber. The light is branched into two components, a P-component linearly polarized light that oscillates in the inside and an S-component linearly polarized light that oscillates in a plane perpendicular to the input surface, and one of the components is supplied to a low-pass filter to detect a DC component. An AC component is detected by subtracting the DC component from one component, a ratio between the AC component and the DC component is calculated, and a magnitude of the measured current is detected. , In which the ratio between the AC component and a DC component the sensor fiber material so as to be constant with respect to temperature change, the curvature, selecting the material of the fixed frame.

Further, the present invention provides a conductor through which an alternating current to be measured flows, a sensor fiber having a Faraday effect and disposed so as to surround the conductor, and means for causing light from a light source to enter the sensor fiber; In a photocurrent sensor comprising means for detecting the magnitude of the current to be measured from light transmitted through the sensor fiber, a P-component linearly polarized light that propagates linearly polarized light through the sensor fiber and vibrates in an input plane; Split into two components, an S component and linearly polarized light oscillating in a plane perpendicular to the plane, supplying the P component to a low-pass filter to detect a DC component, and subtracting the DC component from the P component to obtain an AC component. , The ratio between the AC component and the DC component is calculated, the magnitude of the measured current is detected, and the ratio between the AC component and the DC component changes with temperature. The material of the sensor fiber to be constant for the curvature, and selects the material of the fixing frame.

Further, a conductor through which the measured AC current flows;
A sensor fiber having a Faraday effect and disposed so as to surround the conductor, means for causing light from a light source to enter the sensor fiber, and detecting the magnitude of the measured current from the light propagated through the sensor fiber In the photocurrent sensor, means for transmitting linearly polarized light through the sensor fiber and oscillating in the input plane into two components, a P component linearly polarized light and an S component linearly polarized light that oscillates in a plane perpendicular to the input surface. The S component is supplied to a low-pass filter to detect a DC component, an AC component is detected by subtracting the DC component from the S component, and a ratio between the AC component and the DC component is calculated. The sensor fiber material, curvature, and fixed frame are set so as to detect the magnitude of the measurement current, and to make the ratio between the AC component and the DC component constant with respect to temperature change. It is to select the material.

Further, the present invention provides the photocurrent sensor described above, wherein the means for calculating the sum or difference of the ratio between the AC component and the DC component and the means for calculating the time average of the AC component and the DC component are provided. And correcting the sum or difference of the ratio between the AC component and the DC component by using the time average value of the ratio between the AC component and the DC component.

The light intensities P and S of the P component and the S component when the linearly polarized light propagating in the sensor fiber and inclined at 45 degrees are branched into two orthogonal components are expressed by the following equations.

[0014]

## EQU1 ## where P = A (1-sin2.theta.)-(1) S = B (1 + sin2.theta.)-(2) where A and B are constants determined by light intensity and circuit constants.

Here, θ is the rotation angle of the polarization plane, and is given by the sum of the Faraday rotation angle φ and the rotation angle δ due to the bending of the sensor fiber as shown in the following equation.

[0016]

## EQU2 ## θ = φ + δ-(3) φ = nVI-(4) where n is the number of turns of the sensor fiber, V is the Verdet constant,
I is the current to be measured.

The photocurrent sensor of the present invention measures an AC current, φ is an AC component proportional to the measured current, and δ is caused by a change in temperature and can be considered as a DC component.

The ratio between the AC component and the DC component of the P component and the S component is expressed by the following equation in a region where θ is small and can be approximated to θ = sin θ.

[0019]

P (ac) / P (dc) =-2φ / (1-2δ) --- (5) S (ac) / S (dc) = 2φ / (1 + 2δ) --- (6) Verde Assuming that the temperature coefficient of the constant V is positive and the temperature coefficient of the rotation angle δ is also positive, from the equations (5) and (6), P (ac) /
It is clear that P (dc) has a large change with temperature and S (ac) / S (dc) has a small change with temperature.

Conversely, if the temperature coefficient of the rotation angle δ is negative, P (a
c) The change in / P (dc) with temperature is reduced. Therefore,
If the change of the AC component due to the temperature change of the Verdet constant V is made equal to the DC component of the temperature change of the same magnitude, the ratio of the AC component and the DC component of one of the P component and the S component becomes It will not change even if the temperature changes.

Since the change rate of the polarization angle δ with respect to the bending of the sensor fiber and the Verdet constant V representing the sensitivity to the current are determined by the material of the sensor fiber, the ratio of the AC component to the DC component is determined by the sensor fiber. The rate of change of the bending with respect to the temperature may be adjusted.

This can be achieved by selecting the radius of curvature of the sensor fiber and the coefficient of thermal expansion of the frame material for fixing the sensor fiber.

[0023]

Embodiments of the present invention will be described below with reference to FIG. The sensor fiber 2 is provided so as to go around the outer periphery of the conductor 1 through which the measured AC current flows, and the sensor fiber 2 is fixed to the fixed frame 3. The sensor fiber 2 is made of quartz glass or lead glass, and the fixed frame 3 is
For example, it is made of stainless steel (SUS).

The light emitted from the light source 4 propagates through the light transmitting fiber 5, is converted into linearly polarized light by the polarizer 6, and propagates through the sensor fiber 2. The propagated light passes through the optical lens 7
a) Only one of orthogonal components of linearly polarized light is transmitted through the analyzer 8, and is input to the photodetector 11 through the lens 7b and the light receiving fiber 10.

In the following description, two orthogonal directions are determined by the analyzer 8.
The case where the S component is detected when the components are P and S will be described. However, the P component can also be detected. Photodetector 11
Is separated into a DC component S (dc) and an AC component S (ac). As shown in FIG. 2, one of the optical signals is input to the low-pass filter 12 and the DC component S
By detecting (dc) and subtracting the output S (dc) from the S component, the AC component S (ac) can be detected. And
The divider 13 calculates the ratio S (ac) / S (d
c) can be calculated to obtain the output of Equation 6.

[0026]

S (ac) / S (dc) = 2φ / (1 + 2δ) (6) The temperature coefficient of the Verdet constant V of the sensor fiber giving the Faraday rotation angle φ has a positive value, and the fiber material Although it depends, it is about 0.01% / ° C. Since the numerator of Equation 6 changes with temperature according to the temperature coefficient of the Verdet constant V, if the value of the denominator also changes at the same ratio as the numerator, the output will be constant with respect to temperature.

Therefore, when the polarization angle δ due to the bending of the sensor fiber 2 is determined by selecting the curvature of the sensor fiber 2, the material of the fixing frame 3 and the method of fixing the sensor fiber 2,
It is possible to make the value of Equation 6 constant with respect to temperature.
The larger the curvature of the sensor fiber, the larger the polarization angle δ,
Since the change in the curvature of the sensor fiber increases as the coefficient of thermal expansion of the fixed frame 3 increases, the rate of change of the AC component and the change in the DC component with respect to the temperature can be made equal by selecting the curvature of the sensor fiber and the coefficient of thermal expansion.

In the embodiment of FIG. 2, when the temperature coefficient of the DC component caused by the change in the polarization angle due to the bending of the sensor fiber is the same as that of the AC component caused by the Verdet constant V, and the coefficient is positive. Was explained.

When the temperature coefficient of the change in the polarization angle due to the bending of the sensor fiber is negative, the ratio between the AC component and the DC component is output using only the other orthogonal light intensity component P, and A stable output with respect to temperature can be obtained. The selection of the two orthogonal components can be easily made depending on the direction of the optical axis passing through the analyzer 8. As described above, according to the present invention, a stable output with respect to the temperature can be obtained without controlling the temperature of the sensor fiber, so that the current can be detected with high accuracy.

Next, another embodiment of the present invention will be described with reference to FIG. In FIG. 1, the light output from the light source 4 is such that linearly polarized light propagates through the sensor fiber 2 via the light transmitting fiber 5, and the propagated light is split into two orthogonal polarization components by the polarization beam splitter 9. Then, the photodetectors 11a,
11b.

Assuming that the optical signal is a P component and an S component, the ratio between the DC component and the AC component can be obtained from the dividers 13a and 13b by the above-described circuit configuration. Divider 13b
The signal VI is obtained by inverting the sign of the output of (1) and averaging the added value.

[0032]

## EQU5 ## VI = -2φ / (1-4δ ² )-(7) Since δ is much smaller than 1, the denominator of VI can be regarded as 1. Therefore, VI varies with temperature because it is proportional to the temperature coefficient of the Verdet constant. But,
Since the P and S signals are averaged, common mode noise due to power supply fluctuations and electromagnetic noise generated on the circuit can be canceled out, so that highly accurate current detection becomes possible.

The current to be measured according to the present invention is an alternating current, and the Faraday rotation angle φ can be expressed by the following equation using Equation 4.

[0034]

Φ = nVKsin (ωt) (8) where K is the current amplitude, ω is the angular frequency, and t is time.

In FIG. 1, each output of the dividers 13a and 13b is used as an rms circuit 15a for calculating an effective value of an AC signal.
15b, and calculating each effective value, the output is as follows.

[0036]

│P│ = 2nVK / (1-2δ) --- (9) │S│ = 2nVK / (1 + 2δ) --- (10) If the time period for calculating the effective value is increased, the circuit becomes Is random in time, the effect can be reduced. Therefore, when the detection amount of the photocurrent sensor is the effective value of the alternating current, one of the P component and the S component that is stable with respect to the temperature may be output.

When the detection amount of the photocurrent sensor is the instantaneous value of the alternating current and the P component is stable with respect to the temperature, the correction circuit shown in FIG. , Signal VI, the output V2 is obtained.

[0038]

Ε = 2 | P | / (| P | + | S |) (11) V2 = −2nVKsin (ωt) / (1-2δ) (12) Denominator of Equation 12, Since the rate of change of the molecule with respect to the temperature is the same, it is possible to configure a current sensor that is stable with respect to the temperature change and is less affected by noise generated on the circuit.

1 and 2, which are the embodiments of the present invention, realize the light intensity signal by an analog circuit. Needless to say, such a signal processing method can also be configured with a digital circuit.

FIG. 3 shows a configuration diagram of an embodiment of the present invention. The configuration of the optical system is the same as the configuration shown in FIG. 1 described above. The P and S signals may be converted into digital signals by the A / D converters 18 a and 18 b, and Equation 12 may be calculated on a computer 19 program.

[0041]

According to the present invention, it is possible to realize a current sensor that is stable against temperature changes and is less affected by noise generated on a circuit without requiring a temperature control mechanism.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a current sensor of the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the current sensor of the present invention.

FIG. 3 is a configuration diagram showing another embodiment of the current sensor of the present invention.

FIG. 4 is a schematic diagram illustrating an arrangement state of a sensor fiber.

[Explanation of symbols]

Reference numeral 1: a conductor through which a current to be measured flows, 2: a sensor fiber, 3
... Fixed frame, 4 ... Light source, 5 ... Transmission fiber, 6 ... Polarizer, 7 ... Lens, 8 ... Analyzer, 9 ... Polarized beam splitter,
10: light receiving fiber, 11: photodetector, 12: low-pass filter, 13: divider, 14: amplifier, 15: rm
s circuit, 16: correction coefficient operation circuit, 17: multiplier, 18
... A / D, 19 ... Calculator.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiyuki Kubota 7-2-1, Omika-cho, Hitachi City, Ibaraki Pref. Hitachi, Ltd. Power & Electricity Development Division (72) Inventor Tokio Yamagoku Hitachi, Ibaraki 1-1-1, Kokubuncho Kokubu Plant, Hitachi, Ltd. (72) Inventor Kiyoshi Kurosawa 4-1 Egasakicho, Tsurumi-ku, Yokohama, Kanagawa Prefecture Inside Tokyo Electric Power Company (72) Inventor Kazunori Yamashita Kanagawa Prefecture 4-1, Egasakicho, Tsurumi-ku, Yokohama-shi Tokyo Electric Power Company F-term (reference) 2G025 AA09 AA11 AB10 AC06

Claims (4)

[Claims] 1. A conductor through which an alternating current to be measured flows, a sensor fiber having a Faraday effect and disposed so as to surround the conductor, means for causing light from a light source to enter the sensor fiber, and the sensor fiber A light current sensor having means for detecting the magnitude of the current to be measured from the light propagated through the sensor fiber, wherein linearly polarized light that propagates linearly polarized light through the sensor fiber and vibrates in the input plane is perpendicular to the input plane. It splits into two components, the S component and linearly polarized light oscillating on the surface, supplies one of the components to a low-pass filter to detect a DC component, and subtracts the DC component from the one component to obtain an AC component. Detecting, calculating the ratio between the AC component and the DC component, and detecting the magnitude of the current to be measured, and the ratio between the AC component and the DC component with respect to a temperature change. The photocurrent sensor is characterized by selecting the material of the sensor fiber, the curvature, and the material of the fixed frame so as to be constant. 2. A conductor through which an alternating current to be measured flows, a sensor fiber having a Faraday effect and disposed so as to surround the conductor, means for causing light from a light source to enter the sensor fiber, and the sensor fiber A photocurrent sensor comprising means for detecting the magnitude of the current to be measured from the light propagated through the P-component linearly polarized light that oscillates in the input plane by propagating linearly polarized light through the sensor fiber; Branched into two components with linearly polarized S-component oscillating on a flat surface, supplying the P-component to a low-pass filter to detect a DC component, and subtracting the DC component from the P-component to detect an AC component. Calculating the ratio between the AC component and the DC component to detect the magnitude of the current to be measured, and ensuring that the ratio between the AC component and the DC component is constant with respect to a temperature change. A material, a curvature, and a material of a fixed frame of the sensor fiber are selected as described above. 3. A conductor through which an alternating current to be measured flows, a sensor fiber having a Faraday effect and disposed so as to surround the conductor, means for causing light from a light source to enter the sensor fiber, and the sensor fiber A light current sensor having means for detecting the magnitude of the current to be measured from the light propagated through the sensor fiber, wherein linearly polarized light that propagates linearly polarized light through the sensor fiber and vibrates in the input plane is perpendicular to the input plane. Branching into two components with an S component linearly polarized light oscillating on the surface, supplying the S component to a low-pass filter to detect a DC component, and subtracting the DC component from the S component to detect an AC component, The ratio between the AC component and the DC component is calculated to detect the magnitude of the measured current, and the ratio between the AC component and the DC component becomes constant with respect to temperature change. So that the material of the sensor fiber,
A photocurrent sensor characterized by selecting a curvature and a material of a fixed frame. 4. The photocurrent sensor according to claim 1, wherein a means for calculating a sum or difference of a ratio between the AC component and the DC component, and a means for calculating a time average value of the AC component and the DC component. Wherein the sum or difference of the ratio between the AC component and the DC component is corrected using a time average value of the ratio between the AC component and the DC component.