JP7038925B1 - Optical voltage sensor - Google Patents

Abstract

The optical voltage sensor (1) is attached to the light source (21), the electro-optical crystal (11) to which the light emitted from the light source (21) is incident, and the end faces (11a, 11b) of the electro-optical crystal (11) facing each other, respectively. It has a first electrode (12a) and a second electrode (12b) provided, and applies an electric field in the direction perpendicular to the traveling direction of light (Y-axis direction) in the electro-optical crystal (11). An electro-optical crystal is provided with an electrode pair (12) applied to (11) and a detector (41) that receives light emitted from the electro-optical crystal (11) and outputs a detection signal based on the received light. The beam size (W) in the vertical direction (Y-axis direction) of the light at the time of incident on (11) is equal to or larger than the distance (D) between the first electrode (12a) and the second electrode (12b). ..

Description

The present disclosure relates to an optical voltage sensor.

An optical voltage sensor using the Pockels effect, which is an electro-optic effect, has been developed as a method that can measure high voltage at low cost while maintaining high insulation. Although the change in the refractive index due to the Pockels effect is slight, it can be measured as a change in the polarization state of the transmitted light by utilizing the characteristic that anisotropy occurs in the refractive index. For example, an electric field applied to an electro-optical crystal by injecting linearly polarized light into the electro-optical crystal using a polarizing element and measuring the change in the polarization state of the emitted light from the electro-optical crystal as a change in light intensity. That is, the potential difference between both ends of the electro-optical crystal can be obtained.

An optical voltage sensor using the Pockels effect has been put into practical use in AC voltage measurement applications, but has not been put into practical use in DC voltage measurement applications. This is because, in DC voltage measurement applications, the voltage cannot be measured stably for a long time due to the influence of output drift caused by the spatial charge polarization inside the electro-optical crystal. When a DC voltage is applied to an electro-optical crystal, the space charge in the electro-optical crystal moves over time, and the electric field distribution inside the electro-optical crystal changes. In the horizontal modulation method in which the traveling direction of light and the direction in which the electric field is applied are perpendicular to each other, the electric field applied between the electrodes is affected by the phenomenon (DC drift) in which the electric field in the part through which light is transmitted changes with time (DC drift). The voltage cannot be measured stably for a long time.

As a method of measuring the DC voltage while avoiding the influence of the DC drift, a method of adopting a vertical modulation method in which the traveling direction of light and the direction in which the electric field is applied in the electro-optical crystal are in the same direction has been proposed. (See, for example, Patent Document 1). In the vertical modulation method, light is applied between the electrodes because the light passes through both the strengthened and weakened parts of the electro-optic crystal and the integrated value along the direction of the electric field is constant. The voltage can be stably measured for a long time without being affected by the DC drift.

JP-A-2015-11019

However, in the vertical modulation method, since the sensitivity to voltage does not depend on the shape of the electro-optic crystal, it is difficult to set a high sensitivity and realize highly accurate measurement. On the other hand, in the horizontal modulation method, it is difficult to stably measure the DC voltage due to the influence of the DC drift.

The present disclosure has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide an optical voltage sensor capable of stably measuring a DC voltage for a long period of time with high accuracy.

The optical voltage sensor of the present disclosure has a light source, an electro-optical crystal to which light emitted from the light source is incident, and a first electrode and a second electrode provided on the end faces of the electro-optical crystal facing each other, respectively. An electrode pair that applies an electric field in the electro-optical crystal in a direction perpendicular to the traveling direction of the light to the electro-optical crystal, and the light emitted from the electro-optical crystal is received and received by the light. A detector that outputs a detection signal based on the light is provided, and the vertical beam size of the light at the time of incident on the electro-optical crystal is equal to or larger than the distance between the first electrode and the second electrode. Moreover, the light transmitted through the electro-optical crystal is collimated light .

According to the optical voltage sensor of the present disclosure, the DC voltage can be stably measured for a long time with high accuracy.

It is a schematic diagram which shows the structure of the optical voltage sensor which concerns on Embodiment 1. FIG. (A) is a perspective view which shows the light emitting part of the optical voltage sensor which concerns on Embodiment 1, and (B) is a figure which shows the function of the light emitting part. (A) is a perspective view showing a mask as a light-shielding member arranged upstream of an electro-optical crystal, and (B) is a schematic view showing a configuration of an optical voltage sensor provided with a mask. (A) is a perspective view showing an array light source as a light source and a lens array as a beam shaping optical system, and (B) is a schematic diagram showing a configuration of an optical voltage sensor including an array light source and a lens array. .. (A) is a perspective view showing a mask as a light-shielding member arranged downstream of an electro-optical crystal, and (B) is a schematic view showing a configuration of an optical voltage sensor provided with a mask. It is a figure which shows the example of the hardware composition of the control system of the optical voltage sensor which concerns on Embodiment 1. FIG. (A) to (C) are diagrams showing the relationship between the light incident on the electro-optical crystal and the electric field distribution in the electro-optical crystal when a DC voltage is applied to the electro-optical crystal for a long time. It is a figure which shows the example of the time change of the measured voltage by the influence of DC drift. It is a schematic diagram which shows the structure of the optical voltage sensor which concerns on Embodiment 2. It is a perspective view which shows the array detector as the detector of the optical voltage sensor which concerns on Embodiment 2. FIG. (A) is a diagram showing the intensity distribution of the detection signal output from the array detector, and (B) is a diagram showing the intensity distribution of the detection signal homogenized by the signal processing device. It is a schematic diagram which shows the structure of the optical voltage sensor which concerns on Embodiment 3. It is a figure which shows the electrical equivalent circuit of the voltage application part of the optical voltage sensor which concerns on Embodiment 3. FIG. It is a figure which shows the relationship between the applied voltage and the bias voltage which concerns on Embodiment 3. FIG.

Hereinafter, the optical voltage sensor according to the embodiment will be described with reference to the drawings. The following embodiments are merely examples, and the embodiments can be changed as appropriate.

The figure shows the coordinate axes of the XYZ Cartesian coordinate system. The Z-axis is a coordinate axis parallel to the traveling direction of light, and the X-axis and the Y-axis are coordinate axes in a direction orthogonal to the Z-axis. Further, the Y-axis direction is the electric field direction in the electro-optical element. In the figure, the same or similar configurations are designated by the same reference numerals.

Embodiment 1.
FIG. 1 is a schematic diagram showing the configuration of the optical voltage sensor 1 according to the first embodiment. The optical voltage sensor 1 according to the first embodiment is provided on the light source 21, the electro-optical crystal 11 to which the light emitted from the light source 21 is incident, and the end face 11a and the end face 11b of the electro-optical crystal 11 facing each other, respectively. An electrode pair having an electrode 12a and a second electrode 12b of the above, and applying an electric field in a direction (Y-axis direction) perpendicular to the traveling direction (Z-axis direction) of light in the electro-optical crystal 11 to the electro-optical crystal 11. 12 and a detector 41 that receives light emitted from the electro-optical crystal 11 and outputs a detection signal. The first electrode 12a and the second electrode 12b are also referred to as "first and second electrodes 12a and 12b" or "a pair of electrodes 12a and 12b".

In the photovoltage sensor 1, the beam width W, which is the beam size in the vertical direction (Y-axis direction) of light at the time of incident on the electro-optical crystal 11, is equal to or larger than the distance D between the first and second electrodes 12a and 12b. It is configured as follows. Further, in FIG. 1, the first and second electrodes 12a and 12b are in close contact with the end faces 11a and 11b of the electro-optical crystal 11, respectively.

Further, the optical voltage sensor 1 includes a beam shaping optical system 22, a polarizing element 31, a 1/4 wave plate (wave plate 32), an analyzer 33, and a lens 42. Further, the optical voltage sensor 1 includes a voltage application unit 10 that applies a voltage V to the electro-optical crystal 11.

Further, the optical voltage sensor 1 has a voltage (for example, a DC voltage) applied between the first and second electrodes 12a and the second electrode 12b based on the detection signal output from the detector 41. Further, a signal processing unit 50 for calculating V50 is provided. In FIG. 1, the signal processing unit 50 includes a signal processing device 51 and an output device 52.

The light source 21 and the beam shaping optical system 22 form a light projecting unit 20 that projects light onto the electro-optical crystal 11. The lens 42 and the detector 41 form a light receiving unit 40. Further, a decoder 31 and a 1/4 wave plate (wave plate 32) that control the polarization state of the incident light on the electro-optical crystal 11 and an analyzer 33 that controls the polarization state of the light emitted from the electro-optical crystal 11. Form the polarization control optical system 30.

The voltage application unit 10 includes an electro-optical crystal 11 and first and second electrodes 12a and 12b provided on opposite end faces 11a and 11b of the electro-optic crystal 11. The electro-optical crystal 11 is an optical crystal having a Pockels effect, which is a primary electro-optical effect. The Pockels effect is an effect in which when an electric field is applied to the electro-optical crystal 11 from the outside, the polarization state of the electro-optical crystal 11 changes, and the refractive index of the electro-optical crystal 11 changes in proportion to the electric field. When the Pockels effect occurs in the electro-optical crystal 11, the refractive index of the electro-optical crystal 11 becomes anisotropic. Light is generally represented by the synthesis of two polarization components whose vibration directions are orthogonal to each other, and when transmitted through an electro-optical crystal 11 having an anisotropic refractive index, the two polarization components have a phase difference (that is, a polarization phase difference). Occurs. In the Pockels effect, the polarization phase difference is proportional to the strength of the electric field applied to the electro-optical crystal 11, so by measuring the change in the polarization state of the light transmitted through the electro-optic crystal 11 using a polarizing element, The potential difference between the first and second electrodes 12a and 12b provided on the end faces 11a and 11b of the electro-optical crystal 11 facing each other can be obtained. The electro-optical crystal 11 includes optical crystals having a Pockels effect, such as LiNbO ₃ , LiTaO ₃ , ADP (NH ₄ H ₂ PO ₄ ), KDP (H ₂ PO ₄ ), SiO ₂ (crystal), and Bi ₁₂ . Crystals such as SiO ₂₀ , Bi ₁₂ GeO ₂₀ , Bi ₄ Ge ₃ O ₁₂ , ZnS, ZnTe, etc. can be used.

The first and second electrodes 12a and 12b function as electrodes for applying a voltage V to the electro-optical crystal 11, and the traveling direction of the light incident on the electro-optical crystal 11 and the electric field direction applied to the electro-optical crystal 11 are set. It is formed in close contact with two opposing end faces 11a and 11b of the electro-optical crystal 11 so as to be vertical. For example, when the distance between the first and second electrodes 12a and 12b is set to 10 mm, a voltage up to about 10 kV that does not cause dielectric breakdown in the atmosphere can be applied to the electro-optical crystal 11. When there is a spatial gap between the electro-optical crystal 11 and the first and second electrodes 12a and 12b, the voltage to be measured is divided between the electro-optical crystal 11 and the spatial gap, and the voltage V is accurately determined. It becomes difficult to measure. Therefore, it is desirable that the first and second electrodes 12a and 12b are formed in close contact with the electro-optical crystal 11 by vapor deposition or sputtering. The constituent materials of the first and second electrodes 12a and 12b may be any material having conductivity. For example, the constituent materials of the first and second electrodes 12a and 12b are aluminum (Al), gold (Au), silver (Ag), copper (Cu), chromium (Cr), or any of these. Or an alloy of two or more metals can be used.

The light projecting unit 20 includes a light source 21 and a beam shaping optical system 22. As the light source 21, a light emitting diode, a semiconductor laser, a solid-state laser, a gas laser, or the like can be used. The light emitted from the light source 21 has a long wavelength so as not to cause an internal photoelectric effect (that is, an effect that the electric resistance of the insulator is lowered by irradiation with light having a short wavelength and the current easily flows). It is desirable to use infrared light with a wavelength of 750 nm or more. The beam shaping optical system 22 collimates the light emitted from the light source 21 (that is, converts the light emitted from the light source into parallel light rays), and the beam size is equal to or larger than the distance between the first and second electrodes 12a and 12b. Generates a beam that is. Here, the beam size is a beam size (that is, a beam width W) on an XY plane orthogonal to the traveling direction of light. Further, the beam shaping optical system 22 generates a beam having a spatially uniform light intensity distribution between the first and second electrodes 12a and 12b.

FIG. 2A is a perspective view showing the light projecting unit 20 of the optical voltage sensor 1, and FIG. 2B is a diagram showing the function of the light projecting unit 20. As shown in FIGS. 2A and 2B, for example, the beam shaping optical system 22 has a collimator lens 221 that collimates the light emitted from the light source 21 and a top having a uniform intensity distribution of the collimated Gaussian beam. It can be configured using a beam shaper 222 that converts to a hat-shaped beam. The beam shaper 222 can be configured by using, for example, a diffractive optical element or an aspherical lens. The light emitted from the beam shaper 222 has a beam size (that is, a beam width W) that is the same as or a distance D between the first and second electrodes 12a and 12b via a mask (first mask) 223. It may be adjusted to a slightly larger size.

FIG. 3A is a perspective view showing a mask 223 as a light-shielding member that shields a part of light (for example, a portion on the outer side in the radial direction) arranged upstream of the electro-optical crystal 11. ) Is a schematic diagram showing the configuration of the optical voltage sensor 1a provided with the mask 223. In the example of FIGS. 3A and 3B, the beam shaping optical system 22 is emitted from the light source 21 by using a collimator lens 221 having an outer diameter sufficiently larger than the distance between the first and second electrodes 12a and 12b. By collimating the light and extracting only the beam near the center using the mask 223, a beam having a desired cross-sectional shape is generated. Except for this point, the examples of FIGS. 3A and 3B are the same as those of FIG.

FIG. 4A is a perspective view showing an array light source 211 as a light source and a lens array 224 as a beam shaping optical system, and FIG. 4B is a photovoltage sensor including an array light source 211 and a lens array 224. It is a schematic diagram which shows the structure of 1b. As shown in FIGS. 4A and 4B, a beam diameter is used by using an array light source 211 having a plurality of two-dimensionally arranged light emitting elements and a lens array 224 having a plurality of two-dimensionally arranged microlenses. A beam with a desired intensity distribution with a flattened intensity distribution in the direction may be generated. Except for this point, the examples of FIGS. 4A and 4B are the same as those of FIG.

The polarization control optical system 30 includes a polarizing element 31, a wave plate 32, and an analyzer 33. The splitter 31 is an optical element that is arranged between the light source 21 and the electro-optical crystal 11 and extracts linearly polarized light from the light emitted from the light projecting unit 20. The wave plate 32 is an optical element that is arranged between the polarizing element 31 and the electro-optical crystal 11 and converts linearly polarized light that has passed through the substituent 31 into circular or elliptically polarized light. As the wave plate 32, a 1/4 wave plate that converts linearly polarized light into circularly polarized light is generally used. However, when the electro-optical crystal 11 or other optical element has natural birefringence, a wave plate other than the 1/4 wave plate or a variable wave plate whose polarization state can be adjusted may be used as the wave plate 32. The analyzer 33 is an optical element arranged between the electro-optical crystal 11 and the detector 41 and extracting linearly polarized light from the light transmitted through the electro-optical crystal 11. The analyzer 33 is arranged so as to transmit linearly polarized light in a direction parallel to or perpendicular to the linearly polarized light transmitted through the polarizing element 31. As the analyzer 33, a polarizing element that transmits only a polarization component in one direction of light, a polarization beam splitter that splits light into two orthogonal polarization components, or the like can be used.

The light receiving unit 40 includes a detector 41 and a lens 42. The detector 41 is a photodetector that detects light intensity as an electric signal by light-electric conversion (O / E conversion). As the detector 41, for example, a photodiode having high sensitivity to the wavelength of the light emitted by the light source 21 can be used. The lens 42 is an optical element that collects the light transmitted through the electro-optical crystal 11 on the detector 41. When the detector 33 is a polarization beam splitter, the detector 41 and the lens 42 may be provided with two sets in order to detect the light of two separated orthogonal polarization components.

FIG. 5A is a perspective view showing a mask (second mask) 43 as a light-shielding member that shields a part of light (for example, a portion outside in the radial direction) arranged downstream of the electro-optic crystal 11. 5 (B) is a schematic view showing the configuration of the optical voltage sensor 1c provided with the mask 43. When there is a possibility that the light that is not incident on the electro-optical crystal 11 is received by the detector 41, as shown in FIGS. 5A and 5B, only the light that is incident on the electro-optical crystal 11 is the detector 41. A mask 43 may be provided upstream of the lens 42 so that light can be received by the lens 42. In that case, the mask 43 may be inserted not only upstream of the lens 42 but also at any position between the light source 21 and the detector 41.

The signal processing unit 50 includes a signal processing device 51 and an output device 52. The signal processing device 51 calculates the voltage V applied between the first and second electrodes 12a and 12b based on the electric signal output by the detector 41. When the light that is not incident on the electro-optical crystal 11 is received by the detector 41, the signal processing device 51 removes the signal component of the light that is not incident on the electro-optical crystal 11 as an offset to reduce the voltage V. It is desirable to calculate.

The output device 52 converts the voltage V calculated by the signal processing device 51 into an analog or digital value and outputs the voltage V. Further, the output device 52 may display the voltage V calculated by the signal processing device 51 in analog or digital using a display.

FIG. 6 is a diagram showing an example of the hardware configuration of the control system of the optical voltage sensor 1 according to the first embodiment. The signal processing unit 50 of FIG. 1 can be configured by the processing circuit 100. Further, the processing circuit 100 can be realized by a dedicated circuit, a computer, or the like. In the example of FIG. 6, the processing circuit 100 includes a memory 102 for storing a program as software, a processor 101 such as a CPU (central processing unit) for executing the program, and an auxiliary storage device 103 such as a hard disk device (HDD). The interface 104 and the output circuit 105 are provided. However, the hardware configuration of the control system of the optical voltage sensor 1 is not limited to the example of FIG.

The operation of the optical voltage sensor 1 according to the first embodiment will be described below. The light emitted from the light source 21 is converted into collimated light and light having a beam size equal to or larger than the distance between the first and second electrodes 12a and 12b by the beam shaping optical system 22, and is incident on the polarizing element 31. The splitter 31 extracts linearly polarized light from the incident light. The wave plate 32 converts the linearly polarized light incident through the polarizing element 31 into circularly polarized light. The electro-optical crystal 11 is an elliptical type of circularly polarized light incident on the wave plate 32 according to the voltage applied between the first and second electrodes 12a and 12b provided on the facing surface of the electro-optical crystal 11. Convert to polarization. The light emitted from the electro-optic crystal 11 is incident on the analyzer 33, and the light is output only in the polarized state in one direction. The amount of light output from the analyzer 33 changes according to the ellipticity of the elliptically polarized light converted by the electro-optic crystal 11. Assuming that the amount of light I _IN incident on the electro-optic crystal 11 and the amount of light output from the analyzer 33 are I _OUT , I _OUT / I _IN is expressed by the following equation (1). Here, θ is a polarization phase difference caused by applying a voltage to the electro-optical crystal 11.

Further, there is a relationship represented by the following equation (2) between the polarization phase difference θ and the voltage V applied to the electro-optic crystal 11 (that is, between the first and second electrodes 12a and 12b). ..

Here, L is the magnitude in the same direction as the light traveling direction (Z-axis direction) of the electro-optical crystal 11 (that is, the optical path length), and D is the electric field direction (Y-axis direction) applied to the electro-optical crystal 11. ), And A is a Pockels coefficient, which is a coefficient indicating the sensitivity of the electro-optical crystal 11 to a voltage.

When no voltage is applied between the first and second electrodes 12a and 12b, I _OUT / I _IN = 1/2. On the other hand, when a voltage is applied between the first and second electrodes 12a and 12b, a polarization phase difference θ is generated in proportion to the voltage according to the above-mentioned principle of the Pockels effect, and I _OUT / I _IN changes. .. In particular, when the voltage is small, the equation (1) can be approximated, and I _OUT / I _IN changes in proportion to the voltage. The light output from the detector 33 is collected by the lens 42 on the detector 41 and converted into an electric signal according to the light intensity. The signal processing device 51 uses the relationship between the equation (1) and the equation (2) based on the electric signal output by the detector 41, and the voltage applied between the first and second electrodes 12a and 12b. Calculate V. The voltage value calculated by the signal processing device 51 is converted into an analog or digital value by the output device 52 and output.

The optical voltage sensor 1 according to the first embodiment is collimated light and the beam size is equal to or larger than the distance between the first and second electrodes 12a and 12b, and further, the light is emitted between the first and second electrodes 12a and 12b. Light having a spatially uniform intensity distribution is incident on the electro-optical crystal 11. Hereinafter, the reason why the influence of the direct current drift can be avoided by making the light having the above characteristics incident on the electro-optic crystal 11 will be described.

7 (A) to 7 (C) are diagrams showing the relationship between the light incident on the electro-optical crystal 11 and the electric field distribution in the electro-optical crystal 11 when a DC voltage is applied to the electro-optical crystal 11 for a long time. be. FIG. 7A shows a case where light is incident only on the central portion between the first and second electrodes 12a and 12b in close contact with the electro-optical crystal 11 in the horizontal modulation method (comparative example). FIG. 7B shows a case (embodiment) in which spatially uniform light is incident on the entire space between the first and second electrodes 12a and 12b in close contact with the electro-optical crystal 11 in the horizontal modulation method. .. When a DC voltage is applied to the electro-optical crystal 11, the electric field distribution inside the electro-optical crystal 11 becomes non-uniform over time due to the movement of space charges. For example, when the electric fields are concentrated in the vicinity of the first and second electrodes 12a and 12b, the electric fields E1 and E5 in the vicinity of the first and second electrodes 12a and 12b are the electric fields E2 in the vicinity of the center of the electro-optic crystal 11. It will be larger than ~ E4. Therefore, as shown in FIG. 7A, when the light passes only through the central portion of the electro-optic crystal 11 (when the measurement light is affected by the electric field E3), the voltage to be measured is measured as shown in FIG. The value decreases over time. On the other hand, as shown in FIG. 7B, when spatially uniform light passes through the entire electro-optic crystal 11, even if an electric field non-uniformity occurs inside the electro-optic crystal 11, the measured light is the first. The integrated value of the electric field between the first and second electrodes 12a and 12b, that is, the phase difference equal to the voltage applied between the first and second electrodes 12a and 12b is received, and the DC voltage is applied for a long time. It can be measured stably.

Further, FIG. 7C shows an example (comparative example) of a vertical modulation method in which the traveling direction of light and the direction in which an electric field is applied are the same in the electro-optical crystal 11. Even in the vertical modulation method, the measurement light passes through both the strengthened part and the weakened part of the electric field in the electro-optic crystal, and the integrated value along the electric field direction is constant, so that it is applied between the electrodes. The voltage can be measured stably for a long time. On the other hand, in the case of the vertical modulation method, the polarization phase difference θ with respect to the voltage V applied to the electro-optical crystal 11 (between the first and second electrodes 12a and 12b, in this case, the transparent electrode) is the electro-optical crystal. Since it does not depend on the shape of 11 (for example, the path length L and the thickness D), the measurement accuracy cannot be improved by changing the shape of the electro-optical crystal 11.

On the other hand, the optical voltage sensor 1 according to the first embodiment adopts the horizontal modulation method, and as shown in the equation (2), the shape (for example, the path length L and the thickness) of the electro-optical crystal 11 By changing D), the polarization phase difference θ with respect to the voltage V can be set large. Therefore, by changing the shape of the electro-optical crystal 11, it is possible to measure the DC voltage with high accuracy.

Embodiment 2.
FIG. 9 is a schematic diagram showing the configuration of the optical voltage sensor 2 according to the second embodiment. The optical voltage sensor 2 according to the second embodiment is provided with a collimator lens 221 as a beam shaping optical system of the light projecting unit 20a and an array detector 411 as a detector of the light receiving unit 40a. It is different from the optical voltage sensor 1 according to 1. In the description of the second embodiment, the same description as that of the first embodiment will be omitted.

The collimator lens 221 collimates the light emitted from the light source 21 and generates a beam having a beam size (that is, a beam width W) equal to or larger than the distance D between the first and second electrodes 12a and 12b. The beam generated by the collimator lens 221 becomes light having a spatially non-uniform intensity distribution.

FIG. 10 is a perspective view showing the array detector 411. The array detector 411 is a photodetector in which a plurality of photodetectors are arranged in a one-dimensional or two-dimensional array. When the size of the portion of the array detector 411 that detects light is equal to or larger than the distance D between the first and second electrodes 12a and 12b, it is not necessary to use the lens 42 to focus the beam.

FIG. 11A is a diagram showing the intensity distribution of the detection signal output from the array detector 411, and FIG. 11B is a diagram showing the intensity distribution of the detection signal homogenized by the signal processing device 51. Is. As shown in FIG. 11A, the signal acquired by the array detector 411 depends on the illuminance distribution of the beam, and has different luminance values for the pixels near the center and at the edges far from the center. When the signal processing device 51 calculates the voltage by adding the brightness values of each pixel, it is strongly affected by the electric field in the high-luminance portion of the electro-optical crystal 11, so that the influence of the DC drift cannot be avoided. .. Therefore, the signal processing device 51 acquires the luminance value of each pixel depending on the illuminance distribution of the beam in a state where no voltage is applied to the electro-optical crystal 11 in advance, and as shown in FIG. 11B, After uniformly correcting the non-uniformity of the brightness value of each pixel, the amount of change in the intensity of the light emitted from the electro-optical crystal 11 is measured, and the voltage is calculated.

In the optical voltage sensor 2 according to the second embodiment, the collimator lens 221 and the array detection, which are general-purpose beam shaping optical systems, are not used without using the beam shaping optical system 22 provided with a special light source or a special optical element. By using the device 411, the same effect as that of the optical voltage sensor 1 according to the first embodiment can be obtained.

Other than the above, the second embodiment is the same as the first embodiment.

Embodiment 3.
In the optical voltage sensor according to the first and second embodiments, for example, when trying to directly measure a high voltage of 100 kV, it is necessary to separate the first and second electrodes 12a and 12b by about 100 mm due to the limitation of electrical insulation. be. However, it is not realistic to create collimated light having a beam size of about 100 mm because the beam shaping optical system 22 or the collimator lens 221 becomes large.

Therefore, in the third embodiment, by providing an electrode that is not in contact with the electro-optical crystal 11 as an electrode to which a high voltage is applied, even if the magnitude of the electro-optical crystal 11 in the electric field direction is about 10 mm. Provided is an optical voltage sensor capable of directly measuring a high voltage exceeding 100 kV. In addition, for example, the technique related to Patent Document 2 is described.

International Publication No. 2020/152820

FIG. 12 is a schematic diagram showing the configuration of the optical voltage sensor 3 according to the third embodiment. The optical voltage sensor 3 according to the third embodiment is different from the optical voltage sensors of the first and second embodiments in the following points (1) to (4).
(1) A point provided with a high-voltage conductor 13 to which a voltage to be detected is applied, which is arranged away from the electro-optical crystal 11.
(2) A bias potential V _b is applied to the bias electrode 16 arranged between the first electrode 12a and the high-voltage conductor 13 apart from both the electro-optical crystal 11 and the high-voltage conductor 13, and the bias electrode 16. A point equipped with a bias power supply 53.
(3) The point where the signal processing unit 50 determines the bias potential based on the detection signal output from the detector 41.
(4) A point where the ground conductor 14 as an electrode is connected to the second electrode 12b.
(5) A point where the crystal upper surface electrode 15 is connected to the upper surface of the first electrode 12a.

The high voltage conductor 13 of the voltage application unit 10a shown in FIG. 12 is a voltage conductor to which a high voltage, which is the voltage to be detected, is applied. The ground conductor 14 is a conductor fixed at a ground potential. The ground conductor 14 is installed on the second electrode 12b that is in close contact with the end face 11b of the electro-optical crystal 11. The crystal top electrode 15 is installed on the first electrode 12a that is in close contact with the end face 11a of the electro-optical crystal 11. The bias electrode 16 is installed so as not to be in contact with the crystal upper surface electrode 15. The signal processing unit 50 controls the bias power supply 53 connected to the bias electrode 16. In the description of the third embodiment, the same description as that of the first and second embodiments will be omitted.

The high voltage conductor 13 is assumed to be a charged portion boosted to reduce Joule loss for power transmission and distribution, and when the voltage is high, a voltage exceeding several hundred kV is applied. For example, the high voltage conductor 13 is a conductor around an electric power device in a substation, an AC / DC converter station, a frequency converter station, or the like.

The ground conductor 14 is installed so as to face the high voltage conductor 13, and its potential is fixed to the ground potential, that is, zero potential, through the ground wire and the ground electrode embedded in the ground. It is desirable that the impedance of the grounding wire and the grounding electrode is sufficiently low, and for example, it is desirable that the class A grounding (grounding resistance value: 10Ω or less) specified in the Japanese Electrical Equipment Technical Standards is secured.

The electro-optic crystal 11 is installed between the ground conductor 14 and the crystal top electrode 15. When there is a spatial gap between the electro-optical crystal 11 and the ground conductor 14 and between the electro-optical crystal 11 and the crystal top electrode 15, the voltage to be measured is divided by the spatial gap between the electro-optical crystal 11 and the crystal top electrode 15. Therefore, it becomes an error factor of voltage measurement. Therefore, first and second electrodes 12a and 12b (in this case, a conductive film) in close contact with the electro-optical crystal 11 are provided on the contact surface between the electro-optical crystal 11 and the crystal top electrode 15 and the ground conductor 14. Therefore, it is desirable to electrically connect the electro-optical crystal 11 and the crystal top electrode 15 and electrically connect the electro-optical crystal 11 and the ground conductor 14.

The crystal top electrode 15 is installed in a non-contact manner with the high voltage conductor 13, the ground conductor 14, and the bias electrode 16. The bias electrode 16 is installed between the high voltage conductor 13 and the crystal upper surface electrode 15, and is supported and fixed by an insulating support provided between the ground conductor 14 and the ground conductor 14. The crystal upper surface electrode 15 has a floating potential and can be induced and controlled according to the potential of the bias electrode 16. The bias power supply 53 is connected to the bias electrode 16 and changes the potential of the bias electrode 16. Since the crystal top electrode 15 and the bias electrode 16 are installed under a high electric field, it is desirable to have a shape that avoids electric field enhancement, such as chamfering the ends.

FIG. 13 is a diagram showing an electrical equivalent circuit of the voltage application unit 10a of the optical voltage sensor 3. The voltage Vo of the high voltage conductor 13 is represented by the following equation (3), _{where V f is} the potential of the crystal top electrode 15 and V _b is the potential of the bias electrode 16.

Here, the capacitance between the crystal upper surface electrode 15 and the high voltage conductor 13 is C ₁ , the capacitance between the crystal upper surface electrode 15 and the ground conductor 14 is C ₂ , and the capacitance between the crystal upper surface electrode 15 and the bias electrode 16. Let C ₃ be the capacitance, R be the electrical resistance of the electro-optical crystal 11, and Q be the charge amount of the crystal top electrode 15.

When measuring the voltage _Vo of the high voltage conductor 13, the charge amount Q causes a measurement error. Therefore, at the start of measurement, the crystal top electrode 15 is grounded and statically eliminated, and Q is set to zero. Further, when the voltage _Vo of the high voltage conductor 13 is a DC voltage, the DC electric field is inside the electro-optical crystal 11 unless the potential V _b of the bias electrode 16 is controlled by following the potential fluctuation of the high voltage conductor 13. Will be applied. Since the electric resistance R of the electro-optical crystal 11 is finite and electric conduction is generated according to the applied electric field, the potential _Vf of the crystal top electrode 15 changes so as to become the same potential as the ground conductor 14 over time. do. This decay time constant τ is represented by the product of the permittivity and the resistivity of the electro-optical crystal 11.

On the other hand, in the optical voltage sensor 3 according to the third embodiment, the potential V _b of the bias electrode 16 is controlled and the internal electric field of the electro-optical crystal 11 is maintained at zero, so that electricity through the electro-optical crystal 11 is obtained. Suppress conduction. The signal processing device 51 calculates the potential V _f applied to the electro-optical crystal 11 based on the detection signal output from the detector 41, and if this value has a value other than zero, the bias power supply 53 is used. By varying the potential V _b of the bias electrode 16 and changing the potential V _f of the crystal top electrode 15, the potential V _b of the bias electrode 16 is set so that the internal electric field of the electro-optical crystal 11 is always zero. Feedback control. The feedback control cycle is set to a time sufficiently shorter than the time constant τ of the electrical conduction of the electro-optical crystal 11. The formula (3) is represented by the formula (4) when the potential V _f of the crystal top electrode 15 is zero and the charge amount Q is zero.

_{FIG. 14 is a diagram showing the relationship between the voltage Vo of the high voltage conductor 13 and the potential (that is, the bias voltage) V b of} the bias electrode 16. As shown in FIG. 14, a proportional relationship is established. The signal processing device 51 calculates the voltage _Vo of the high voltage conductor 13 to be measured from the potential V _b , which is the control voltage of the bias power supply 53, based on the equation (4), and outputs the voltage Vo to the output device 52.

In the optical voltage sensor 3 according to the third embodiment, since the electro-optical crystal 11 is not in contact with the high voltage conductor 13, unlike the first and second embodiments, the high voltage is directly measured without stepping down by a voltage divider. It becomes possible to do. Further, since the internal electric field of the electro-optical crystal 11 is feedback-controlled so as to be always zero, the influence of the DC drift can be avoided and the DC voltage can be stably measured for a long time.

On the other hand, depending on the convenience of the high voltage equipment in which the optical voltage sensor 3 according to the third embodiment is installed, there is a possibility that the distance between the high voltage conductor 13 and the ground conductor 14 must be sufficiently separated. Further, even when the high voltage conductor 13 and the ground conductor 14 can be brought close to each other, when a high voltage higher than a certain level is applied to the crystal upper surface electrode 15, the crystal upper surface electrode 15 is charged. It causes deterioration of measurement accuracy. Therefore, in order to prevent the crystal top electrode 15 from being charged, it is necessary to keep the distance between the high voltage conductor 13 and the electro-optic crystal 11 to a distance where charging does not occur. In these cases, the voltage value applied to the electro-optical crystal 11 decreases, so that it becomes difficult to secure the measurement accuracy when the vertical modulation method in which the sensitivity to the voltage cannot be set high is adopted. On the other hand, in the optical voltage sensor 3 according to the third embodiment, by adopting the horizontal modulation method, the shape of the electro-optical crystal 11 (for example, the path length L and the thickness D) is shown in the equation (2). By changing the above, the polarization phase difference θ with respect to the voltage V can be set large, that is, the sensitivity can be set high. Therefore, it becomes easy to secure the measurement accuracy.

Further, as shown in FIG. 7A, when the horizontal modulation method of the comparative example in which light is partially passed through the electro-optical crystal 11 is adopted, the laser is used even when no voltage is applied to the electro-optical crystal 11. Since space charges move due to the influence of light and temperature changes and output drift occurs, it is difficult to measure the DC voltage with high accuracy and for a long period of time. In the optical voltage sensor 3 according to the third embodiment, as shown in FIG. 7B, light having a beam width W of a beam size equal to or larger than the distance D between the first and second electrodes 12a and 12b on the electro-optic crystal 11. By incidenting the voltage, output drift can be avoided, and high-precision and long-term stable voltage measurement becomes possible.

Other than the above, the third embodiment is the same as the first or second embodiment. Further, the configuration using the high voltage conductor 13 and the ground conductor 14 described in the third embodiment can be applied to any of the optical voltage sensors described in the first and second embodiments.

Modification example.
The configuration shown in the above-described embodiment shows an example of the contents of the present disclosure, can be combined with another known technique, and is one of the configurations as long as it does not deviate from the gist of the present disclosure. It is also possible to omit or change the part.

1, 1a, 1b, 1c, 2, 3 Photovoltage sensor, 10, 10a voltage application part, 11 electro-optical crystal, 11a, 11b end face, 12 electrode pair, 12a first electrode, 12b second electrode, 13 high Voltage conductor, 14 ground conductor, 15 crystal top electrode, 16 bias electrode, 20, 20a floodlight, 21 light source, 211 array light source, 22 beam shaping optics, 221 collimator lens, 222 beam shaper, 223 mask, 224 lens array , 30 Voltage control optics, 31 Polarizer, 32 Wave plate, 33 Detector, 40, 40a Receiver, 41 Detector, 411 Array detector, 42 Lens, 43 Mask, 50 Signal processing unit, 51 Signal processing equipment, 52 output device, 53 bias power supply.

Claims (14)

Light source and
An electro-optic crystal to which the light emitted from the light source is incident, and
The electro-optic crystal has a first electrode and a second electrode provided on the end faces of the electro-optic crystal facing each other, and an electric field in a direction perpendicular to the traveling direction of the light in the electro-optic crystal is applied to the electro-optic crystal. With the electrode pair to be applied,
A detector that receives the light emitted from the electro-optical crystal and outputs a detection signal based on the received light.
Equipped with
The light having a beam size in the vertical direction of the light at the time of incident on the electro-optical crystal is equal to or larger than the distance between the first electrode and the second electrode and is transmitted through the electro-optical crystal. Is the collimated light
An optical voltage sensor characterized by that. The photovoltage sensor according to claim 1, wherein the first electrode and the second electrode are in close contact with the end face of the electro-optical crystal. The optical voltage sensor according to claim 1 or 2, wherein the detector is an array detector having a plurality of photodetecting elements arranged two-dimensionally. The optical voltage sensor according to any one of claims 1 to 3, further comprising a signal processing unit that calculates a voltage applied to the electrode pair based on the detection signal. The fourth aspect of claim 4 is characterized in that the signal processing unit calculates the voltage by excluding a signal component based on light that is not incident on the electro-optical crystal from the detection signal output from the detector. Optical voltage sensor. The optical voltage sensor according to claim 4 or 5, wherein the signal processing unit performs processing for equalizing the intensity distribution in the vertical direction of the detection signal output from the detector. A high-voltage conductor arranged away from the electro-optic crystal,
A bias electrode disposed between the first electrode and the high-voltage conductor, away from the electro-optical crystal and the high-voltage conductor.
A bias power supply that applies a bias potential to the bias electrode, and
A signal processing unit that determines the bias potential based on the detection signal output from the detector, and
Further prepare
The optical voltage sensor according to any one of claims 1 to 3, wherein the signal processing unit calculates the potential of the high voltage conductor. Light source and
An electro-optic crystal to which the light emitted from the light source is incident, and
The electro-optic crystal has a first electrode and a second electrode provided on the end faces of the electro-optic crystal facing each other, and an electric field in a direction perpendicular to the traveling direction of the light in the electro-optic crystal is applied to the electro-optic crystal. With the electrode pair to be applied,
A detector that receives the light emitted from the electro-optical crystal and outputs a detection signal based on the received light.
A high-voltage conductor arranged away from the electro-optic crystal,
A bias electrode disposed between the first electrode and the high-voltage conductor, away from the electro-optical crystal and the high-voltage conductor.
A bias power supply that applies a bias potential to the bias electrode, and
A signal processing unit that determines the bias potential based on the detection signal output from the detector, and
Equipped with
The vertical beam size of the light at the time of incident on the electro-optic crystal is equal to or larger than the distance between the first electrode and the second electrode.
The signal processing unit calculates the potential of the high voltage conductor.
An optical voltage sensor characterized by that. The optical voltage sensor according to claim 7 or 8 , wherein the signal processing unit controls the bias potential so as to keep the electric field in the vertical direction applied to the electro-optical crystal to zero. The invention according to any one of claims 1 to 9 , further comprising a first mask which is arranged between the light source and the electro-optical crystal and further blocks a part of the light emitted from the light source. The optical voltage sensor described. Any of claims 1 to 10 , further comprising a second mask that is disposed between the electro-optical crystal and the detector and further blocks a portion of the light emitted from the electro-optical crystal. The optical voltage sensor according to item 1. The optical voltage according to any one of claims 1 to 11 , further comprising a shaping optical system for making the intensity distribution of the light in the vertical direction uniform at the time of incident on the electro-optical crystal. Sensor. A modulator and a wave plate that control the polarization state of the light upstream of the electro-optic crystal,
An analyzer that controls the polarization state of the emitted light from the electro-optical crystal, and
The optical voltage sensor according to any one of claims 1 to 12 , further comprising. The optical voltage sensor according to any one of claims 1 to 13 , wherein the light source is an array light source in which a plurality of light emitting elements are arranged one-dimensionally or two-dimensionally.

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