WO2022259353A1

WO2022259353A1 - Optical voltage sensor

Info

Publication number: WO2022259353A1
Application number: PCT/JP2021/021692
Authority: WO
Inventors: 康人橋場; 裕之河野
Original assignee: 三菱電機株式会社
Priority date: 2021-06-08
Filing date: 2021-06-08
Publication date: 2022-12-15
Also published as: JPWO2022259353A1; JP7038925B1

Abstract

An optical voltage sensor (1) comprises a light source (21), an electro-optic crystal (11) that light emitted from the light source (21) falls on, an electrode pair (12) that comprises a first electrode (12a) and second electrode (12b) that are respectively provided on end surfaces (11a, 11b) of the electro-optic crystal (11) that face each other and applies an electrical field to the electro-optic crystal (11) in a direction (Y-axis direction) perpendicular to the direction in which light travels within the electro-optic crystal (11), and a detector (41) that receives light emitted from the electro-optic crystal (11) and outputs a detection signal based on the received light. The beam size (W) of the light in the perpendicular direction (Y-axis direction) when the light falls on the electro-optic crystal (11) is greater than or equal to the distance (D) between the first electrode (12a) and the second electrode (12b).

Description

optical voltage sensor

The present disclosure relates to an optical voltage sensor.

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

Optical voltage sensors using the Pockels effect have been put into practical use for AC voltage measurement, but not for DC voltage measurement. This is because, in direct voltage measurement applications, the voltage cannot be measured stably for a long period of time due to the effect of output drift caused by space charge polarization inside the electro-optic crystal. When a DC voltage is applied to the electro-optic crystal, the space charges in the electro-optic crystal move over time, and the electric field distribution inside the electro-optic crystal changes. In the horizontal modulation method, in which the direction in which the light travels is perpendicular to the direction in which the electric field is applied, the electric field in the area through which the light passes is affected by the phenomenon (DC drift) that changes over time. Voltage cannot be measured stably for a long time.

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

JP 2015-11019 A

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

The present disclosure has been made to solve the above problems, and aims to provide an optical voltage sensor that can stably and accurately measure a DC voltage for a long period of time.

A photovoltage sensor according to the present disclosure includes a light source, an electro-optic crystal on which light emitted from the light source is incident, and first and second electrodes provided on end surfaces of the electro-optic crystal facing each other. an electrode pair for applying an electric field to the electro-optic crystal in a direction perpendicular to the traveling direction of the light in the electro-optic crystal; and a detector that outputs a detection signal based on the light, wherein the beam size in the vertical direction of the light at the time of incidence on the electro-optic crystal is equal to or larger than the distance between the first electrode and the second electrode. It is characterized by

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

1 is a schematic diagram showing a configuration of a photovoltage sensor according to Embodiment 1; FIG. 3A is a perspective view showing a light projecting section of the optical voltage sensor according to Embodiment 1, and FIG. 3B is a diagram showing a function of the light projecting section; FIG. (A) is a perspective view showing a mask as a light shielding member arranged upstream of an electro-optic crystal, and (B) is a schematic diagram showing the configuration of a photovoltage sensor provided with the 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 a photovoltage sensor provided with the array light source and the lens array. . (A) is a perspective view showing a mask as a light shielding member arranged downstream of an electro-optic crystal, and (B) is a schematic diagram showing the configuration of a photovoltage sensor provided with the mask. 3 is a diagram illustrating an example of a hardware configuration of a control system of the photovoltage sensor according to Embodiment 1; FIG. (A) to (C) are diagrams showing the relationship between the light incident on the electro-optic crystal and the electric field distribution in the electro-optic crystal when a DC voltage is applied to the electro-optic crystal for a long period of time. FIG. 10 is a diagram showing an example of temporal change in measured voltage due to the influence of DC drift; FIG. 8 is a schematic diagram showing the configuration of a photovoltage sensor according to Embodiment 2; FIG. 11 is a perspective view showing an array detector as a detector of the photovoltage sensor according to Embodiment 2; (A) is a diagram showing the intensity distribution of detection signals output from an array detector, and (B) is a diagram showing the intensity distribution of detection signals that have been homogenized by a signal processing device. FIG. 10 is a schematic diagram showing the configuration of a photovoltage sensor according to Embodiment 3; FIG. 10 is a diagram showing an electrical equivalent circuit of a voltage applying section of the photovoltage sensor according to Embodiment 3; FIG. 10 is a diagram showing the relationship between applied voltage and bias voltage according to the third embodiment;

A photovoltage sensor according to an embodiment will be described below with reference to the drawings. The following embodiments are merely examples, and the embodiments can be modified as appropriate.

The diagram shows the coordinate axes of the XYZ orthogonal coordinate system. The Z-axis is a coordinate axis parallel to the traveling direction of light, and the X-axis and Y-axis are coordinate axes perpendicular to the Z-axis. Also, the Y-axis direction is the electric field direction in the electro-optical element. In addition, in the drawings, the same reference numerals are given to the same or similar configurations.

Embodiment 1.
FIG. 1 is a schematic diagram showing the configuration of a photovoltage sensor 1 according to Embodiment 1. FIG. The optical voltage sensor 1 according to the first embodiment includes a light source 21, an electro-optic crystal 11 into which light emitted from the light source 21 is incident, and first electrodes provided on the end surface 11a and the end surface 11b of the electro-optic crystal 11 facing each other. and a second electrode 12b for applying an electric field in the direction (Y-axis direction) perpendicular to the light traveling direction (Z-axis direction) in the electro-optic crystal 11 to the electro-optic crystal 11. 12, and a detector 41 for receiving light emitted from the electro-optic crystal 11 and outputting 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 of light in the vertical direction (Y-axis direction) at the time of incidence on the electro-optic crystal 11, is greater than or equal to the interval D between the first and second electrodes 12a and 12b. is configured as Also, 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-optic crystal 11, respectively.

The photovoltage sensor 1 also includes a beam shaping optical system 22 , a polarizer 31 , a quarter wave plate (wave plate 32 ), an analyzer 33 and a lens 42 . The optical voltage sensor 1 also includes a voltage applying section 10 that applies a voltage V to the electro-optic crystal 11 .

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

The light source 21 and the beam shaping optical system 22 constitute a light projecting section 20 that projects light onto the electro-optic crystal 11 . The lens 42 and the detector 41 constitute the light receiving section 40 . A polarizer 31 and a quarter-wave plate (wave plate 32) for controlling the polarization state of light incident on the electro-optic crystal 11, and an analyzer 33 for controlling the polarization state of light emitted from the electro-optic crystal 11. form the polarization control optical system 30 .

The voltage application unit 10 includes an electro-optic crystal 11 and first and

second electrodes

12a and 12b provided on the facing

end surfaces

11a and 11b of the electro-optic crystal 11, respectively. The electro-optic crystal 11 is an optical crystal having the Pockels effect, which is a first-order electro-optic effect. The Pockels effect is an effect that when an electric field is applied to the electro-optic crystal 11 from the outside, the polarization state of the electro-optic crystal 11 changes and the refractive index of the electro-optic crystal 11 changes in proportion to the electric field. When the Pockels effect occurs in the electro-optic crystal 11, the refractive index of the electro-optic crystal 11 becomes anisotropic. Light is generally represented by a combination of two polarized components whose vibration directions are orthogonal to each other. When the light is transmitted through the electro-optic crystal 11 having anisotropy in the refractive index, the two polarized components have a phase difference (that is, a polarization phase difference). occurs. In the Pockels effect, the polarization phase difference is proportional to the intensity of the electric field applied to the electro-optic crystal 11. Therefore, by measuring the change in the polarization state of the light transmitted through the electro-optic crystal 11 using a polarizing element, A potential difference between the first and

second electrodes

12a and 12b provided on the

end surfaces

11a and 11b of the electro-optic crystal 11 facing each other can be obtained. As the electro-optic crystal ₁₁ , an optical crystal having the Pockels effect, such as LiNbO3, _LiTaO3 _, ADP( _NH4H2PO4 ), KDP ₍ _H2PO4 ), _SiO2 ₍ crystal), Bi ₁₂ Crystals such as _SiO20 , _Bi12GeO20 , _Bi4Ge3O12 _, _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-optic crystal 11. It is formed in close contact with two opposing

end surfaces

11a and 11b of the electro-optic 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, the electro-optic crystal 11 can be applied with a voltage of up to about 10 kV, which does not cause dielectric breakdown in the air. When there is a spatial gap between the electro-optic crystal 11 and the first and

second electrodes

12a and 12b, the voltage to be measured is divided by the electro-optic crystal 11 and the spatial gap, and the voltage V can be obtained accurately. difficult to measure. Therefore, it is desirable that the first and

second electrodes

12a and 12b are formed in close contact with the electro-optic crystal 11 by vapor deposition or sputtering. The constituent material of the first and

second electrodes

12a and 12b may be a material having conductivity. For example, the constituent material of the first and

second electrodes

12a and 12b may be 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 section 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 that does not cause the internal photoelectric effect (that is, the effect that the electrical resistance of the insulator decreases and the current flows easily due to the irradiation of light with a short wavelength). It is desirable to use infrared light with a wavelength of 750 nm or longer. The beam shaping optical system 22 collimates the light emitted from the light source 21 (that is, converts the divergent light beams from the light source into parallel light beams) and has a beam size equal to or greater than the distance between the first and second electrodes 12a and 12b. to generate a beam that is Here, the beam size is the beam size (that is, the beam width W) on the XY plane perpendicular to the traveling direction of light. Furthermore, the beam shaping optical system 22 generates a beam with a spatially uniform light intensity distribution between the first and

second electrodes

12a, 12b.

2(A) is a perspective view showing the light projecting section 20 of the photovoltage sensor 1, and FIG. 2(B) is a diagram showing the function of the light projecting section 20. FIG. For example, as shown in FIGS. 2A and 2B, the beam shaping optical system 22 includes a collimator lens 221 that collimates the light emitted from the light source 21, and a top lens with a uniform intensity distribution for the collimated Gaussian cyan beam. It can be configured with a beam shaper 222 that converts it into a hat beam. Beam shaper 222 can be constructed using, for example, a diffractive optical element or an aspherical lens. The light emitted from the beam shaper 222 passes through a mask (first mask) 223 so that the beam size (that is, the beam width W) is equal to or equal to the interval D between the first and

second electrodes

12a and 12b. You can adjust it to be slightly larger.

FIG. 3A is a perspective view showing a mask 223 serving as a light shielding member for shielding a portion of light (for example, a radially outer portion) arranged upstream of the electro-optic crystal 11, and FIG. ) is a schematic diagram showing the configuration of a photovoltage sensor 1a having a mask 223. FIG. 3A and 3B, the beam shaping optical system 22 emits from the light source 21 using a collimator lens 221 whose outer diameter is sufficiently larger than the spacing between the first and

second electrodes

12a, 12b. By collimating the light and extracting only the beam near the center using the mask 223, a beam with 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 provided with the array light source 211 and lens array 224. It is a schematic diagram which shows the structure of 1b. As shown in FIGS. 4A and 4B, the beam diameter is A beam may be produced having a desired intensity distribution with a directional flattened intensity distribution. 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 polarizer 31, a wavelength plate 32, and an analyzer 33. The polarizer 31 is an optical element that is arranged between the light source 21 and the electro-optic crystal 11 and extracts linearly polarized light from the light emitted from the light projecting section 20 . The wave plate 32 is an optical element that is arranged between the polarizer 31 and the electro-optic crystal 11 and converts linearly polarized light that has passed through the polarizer 31 into circularly polarized light or elliptically polarized light. Wave plate 32 is generally a quarter wave plate that converts linearly polarized light into circularly polarized light. However, if the electro-optic crystal 11 or other optical elements have natural birefringence, the wavelength plate 32 may be a wavelength plate other than the quarter wavelength plate or a variable wavelength plate capable of adjusting the polarization state. The analyzer 33 is an optical element that is arranged between the electro-optic crystal 11 and the detector 41 and extracts linearly polarized light from the light that has passed through the electro-optic 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 polarizer 31 . As the analyzer 33, a polarizer that transmits only one polarized component of light, a polarization beam splitter that splits light into two orthogonal polarized 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 electrical signal by optical-electrical 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-optic crystal 11 onto the detector 41 . If the analyzer 33 is a polarizing beam splitter, two sets of the detector 41 and the lens 42 may be provided to detect the two orthogonal polarization components of the separated light.

FIG. 5A is a perspective view showing a mask (second mask) 43 as a light shielding member that shields part of the light (for example, the radially outer portion) arranged downstream of the electro-optic crystal 11. FIG. FIG. 5B is a schematic diagram showing the configuration of the photovoltage sensor 1c provided with the mask 43. As shown in FIG. If light not incident on the electro-optic crystal 11 is likely to be received by the detector 41, only the light incident on the electro-optic crystal 11 is detected by the detector 41 as shown in FIGS. A mask 43 may be provided upstream of the lens 42 so that the light is received at . In this case, the mask 43 may be inserted at any position between the light source 21 and the detector 41 without being limited to the upstream of the lens 42 .

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, 12b based on the electrical signal output by the detector 41. FIG. When light that is not incident on the electro-optic 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-optic crystal 11 as an offset, thereby reducing the voltage V to 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 it. Also, the output device 52 may display the voltage V calculated by the signal processing device 51 in analog or digital form using a display.

FIG. 6 is a diagram showing an example of the hardware configuration of the control system of the photovoltage sensor 1 according to the first embodiment. The signal processing unit 50 in FIG. 1 can be configured by the processing circuit 100 . Also, 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 that stores a program as software, a processor 101 such as a CPU (central processing unit) that executes the program, and an auxiliary storage device 103 such as a hard disk drive (HDD). , an interface 104 and an output circuit 105 . 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 photovoltage sensor 1 according to the first embodiment will be described below. Emitted light from the light source 21 is converted by the beam shaping optical system 22 into collimated light with a beam size equal to or greater than the distance between the first and

second electrodes

12 a and 12 b , and enters the polarizer 31 . The polarizer 31 extracts linearly polarized light from incident light. Wave plate 32 converts linearly polarized light incident through polarizer 31 into circularly polarized light. The electro-optic crystal 11 transforms the incident circularly polarized light through the wavelength plate 32 into an elliptically polarized light according to the voltage applied between the first and

second electrodes

12a and 12b provided on the opposing surfaces of the electro-optic crystal 11. convert to polarized light. The light emitted from the electro-optic crystal 11 is incident on the analyzer 33, and the light is output only in one polarized state. 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-optic crystal 11 .

Further, there is a relationship represented by the following formula (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 size in the same direction as the light traveling direction (Z-axis direction) of the electro-optic crystal 11 (that is, the optical path length), and D is the direction of the electric field applied to the electro-optic crystal 11 (Y-axis direction). ), and A is the Pockels coefficient, which is a coefficient indicating the sensitivity of the electro-optic crystal 11 to voltage.

When no voltage is applied between the first and

second electrodes

12a, 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, according to the principle of the Pockels effect described above, a polarization phase difference θ is generated in proportion to the voltage, and I _OUT /I _IN changes. . Especially for small voltages, equation (1) can be approximated and I _OUT /I _IN varies proportionally with voltage. The light output from the analyzer 33 is condensed by the lens 42 onto the detector 41 and converted into an electrical signal according to the light intensity. The signal processing device 51 calculates the voltage applied between the first and

second electrodes

12a and 12b based on the electrical signal output by the detector 41 and using the relationship of the equations (1) and (2). Calculate V. The voltage value calculated by the signal processing device 51 is converted to an analog or digital value by the output device 52 and output.

The optical voltage sensor 1 according to the first embodiment has collimated light and a beam size equal to or greater than the distance between the first and

second electrodes

12a and 12b, and furthermore, the light is distributed between the first and

second electrodes

12a and 12b. Light having a spatially uniform intensity distribution is made incident on the electro-optic crystal 11 . The reason why the influence of DC drift can be avoided by making the light having the above characteristics incident on the electro-optic crystal 11 will be described below.

7A to 7C are diagrams showing the relationship between the light incident on the electro-optic crystal 11 and the electric field distribution in the electro-optic crystal 11 when a DC voltage is applied to the electro-optic crystal 11 for a long time. be. FIG. 7A shows a case (comparative example) in which light is incident only on the central portion between the first and

second electrodes

12a and 12b in close contact with the electro-optic crystal 11 in the lateral modulation method. 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-optic crystal 11 in the lateral modulation method. . When a DC voltage is applied to the electro-optic crystal 11, the electric field distribution inside the electro-optic crystal 11 becomes non-uniform over time due to movement of space charges. For example, when electric fields are concentrated near the first and

second electrodes

12 a and 12 b, the electric fields E 1 and E 5 near the first and

second electrodes

12 a and 12 b become the electric field E 2 near the center of the electro-optic crystal 11 . ~ larger than E4. Therefore, when the light passes through only the central portion of the electro-optic crystal 11 as shown in FIG. 7A (when the measurement light is affected by the electric field E3), the measured voltage 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 non-uniformity occurs in the electric field inside the electro-optic crystal 11, the measurement light is A phase difference equal to the integrated value of the electric field between the first and

second electrodes

12a, 12b, i.e., the voltage applied between the first and

second electrodes

12a, 12b will be experienced, and the DC voltage will be applied for a long time. Stable measurement is possible.

Also, FIG. 7(C) 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-optic crystal 11 . In the vertical modulation method as well, the measurement light passes through both the part where the electric field is strengthened and the part where the electric field is weakened in the electro-optic crystal, and the integrated value along the electric field direction is constant. voltage can be stably measured for a long period of 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-optic crystal 11 (between the first and

second electrodes

12a and 12b, transparent electrodes in this case) is the electro-optic crystal 11 (eg path length L and thickness D), the measurement accuracy cannot be improved by changing the shape of the electro-optic crystal 11 .

On the other hand, the optical voltage sensor 1 according to the first embodiment adopts the horizontal modulation method, so that the shape of the electro-optic crystal 11 (for example, the path length L and the thickness 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-optic 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 photovoltage sensor 2 according to the second embodiment includes a collimator lens 221 as a beam shaping optical system of the light projecting section 20a and an array detector 411 as a detector of the light receiving section 40a. 1 is different from the optical voltage sensor 1 according to 1. In addition, in the explanation regarding the second embodiment, the explanation similar to that of the first embodiment is omitted.

The collimator lens 221 collimates the light emitted from the light source 21 and generates a beam having a beam size (that is, beam width W) equal to or larger than the distance D between the first and

second electrodes

12a, 12b. The beam generated by the collimator lens 221 has a spatially non-uniform intensity distribution.

10 is a perspective view showing the array detector 411. FIG. The array detector 411 is a photodetector in which a plurality of photodetection elements are arranged in a one-dimensional or two-dimensional array. If the size of the portion of the array detector 411 that detects light is greater than or equal to the distance D between the first and

second electrodes

12a and 12b, the lens 42 need not be used to condense 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. The signal acquired by the array detector 411, as shown in FIG. 11A, depends on the illuminance distribution of the beam, and has different luminance values for pixels near the center and at the edges away from the center. When the signal processing device 51 calculates the voltage by summing the luminance values of the pixels, it is strongly affected by the electric field of the high-luminance portion in the electro-optic crystal 11, and therefore the influence of the DC drift cannot be avoided. . Therefore, the signal processing device 51 obtains the luminance value of each pixel depending on the illuminance distribution of the beam in advance in a state where no voltage is applied to the electro-optic crystal 11, and obtains the luminance value as shown in FIG. 11(B). After uniformly correcting the non-uniformity of the luminance value of each pixel, the amount of change in the intensity of the light emitted from the electro-optic crystal 11 is measured, and the voltage is calculated.

In the optical voltage sensor 2 according to the second embodiment, the collimator lens 221, which is a general-purpose beam shaping optical system, and the array detection are used without using the beam shaping optical system 22 having a special light source or a special optical element. By using the device 411, an effect similar to that of the optical voltage sensor 1 according to the first embodiment can be obtained.

Except for the above, the second embodiment is the same as the first embodiment.

Embodiment 3.
In the photovoltage sensors according to

Embodiments

1 and 2, when a high voltage of, for example, 100 kV is to be directly measured, it is necessary to separate the first and

second electrodes

12a and 12b by about 100 mm due to electrical insulation restrictions. be. However, creating collimated light with a beam size of about 100 mm is not realistic because the beam shaping optical system 22 or the collimator lens 221 becomes large.

Therefore, in Embodiment 3, by providing an electrode that is not in contact with the electro-optic crystal 11 as an electrode to which a high voltage is applied, even if the magnitude of the electric field direction of the electro-optic crystal 11 is about 10 mm, Provided is an optical voltage sensor capable of directly measuring high voltage exceeding 100 kV. Note that, for example, a technique related to Patent Document 2 is described.

WO2020/152820

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 Embodiment 3 differs from the optical voltage sensors according to

Embodiments

1 and 2 in the following points (1) to (4).
(1) A high-voltage conductor 13 to which a voltage to be detected is applied is provided at a distance from the electro-optic crystal 11 .
(2) a bias electrode 16 disposed between the first electrode 12a and the high-voltage conductor 13 and away from both the electro-optic crystal 11 and the high-voltage conductor 13, and applying a bias potential _Vb to the bias electrode 16; and a bias power supply 53 that
(3) The signal processing section 50 determines the bias potential based on the detection signal output from the detector 41 .
(4) A ground conductor 14 as an electrode is connected to the second electrode 12b.
(5) The crystal top surface electrode 15 is connected to the top 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 ground potential. The ground conductor 14 is placed on the second electrode 12b in close contact with the end face 11b of the electro-optic crystal 11. As shown in FIG. The crystal upper surface electrode 15 is placed on the first electrode 12a that is in close contact with the end face 11a of the electro-optic crystal 11. As shown in FIG. The bias electrode 16 is placed so as to be out of contact with the crystal top surface electrode 15 . The signal processing section 50 controls a bias power supply 53 connected to the bias electrode 16 . In addition, in the explanation regarding the third embodiment, explanations similar to those of the first and second embodiments are omitted.

The high-voltage conductor 13 is assumed to be a charged part that is boosted to reduce Joule loss for power transmission and distribution, and when the voltage is high, a voltage exceeding several 100 kV is applied. For example, the high voltage conductors 13 are conductors around power equipment in substations, AC/DC conversion stations, frequency conversion stations, and the like.

The ground conductor 14 is installed so as to face the high-voltage conductor 13, and its potential is fixed to ground potential, ie, zero potential, through a ground wire and a ground electrode embedded in the ground. It is desirable that the impedance of the grounding wire and the grounding electrode is sufficiently low. For example, it is desirable to ensure Class A grounding (grounding resistance value: 10Ω or less) specified in the electrical equipment technical standards of Japan.

The electro-optic crystal 11 is installed between the ground conductor 14 and the crystal upper surface electrode 15 . When there is a spatial gap between the electro-optic crystal 11 and the ground conductor 14 and between the electro-optic crystal 11 and the crystal top electrode 15, the voltage to be measured is divided by the spatial gap between the electro-optic crystal 11 and the crystal top electrode 15. Therefore, it becomes an error factor in voltage measurement. Therefore, first and

second electrodes

12a and 12b (in this case, conductive films) are provided in close contact with the electro-optic crystal 11 on the contact surfaces between the electro-optic crystal 11 and the crystal top electrode 15 and the ground conductor 14. Therefore, it is desirable to electrically connect the electro-optic crystal 11 and the crystal upper surface electrode 15 and electrically connect the electro-optic crystal 11 and the ground conductor 14 .

The crystal upper surface electrode 15 is installed without contact with the high voltage conductor 13, the ground conductor 14, and the bias electrode 16. The bias electrode 16 is placed between the high-voltage conductor 13 and the crystal top electrode 15 and supported and fixed by an insulating support provided between the ground conductor 14 and the ground conductor 14 . The crystal top electrode 15 is at a floating potential and can be induced and controlled according to the potential of the bias electrode 16 . A bias power supply 53 is connected to the bias electrode 16 and varies the potential of the bias electrode 16 . Since the crystal top surface electrode 15 and the bias electrode 16 are placed under a high electric field, it is desirable to have a shape that avoids electric field enhancement, such as round chamfering of the ends.

FIG. 13 is a diagram showing an electrical equivalent circuit of the voltage applying section 10a of the optical voltage sensor 3. As shown in FIG. The voltage V _o of the high-voltage conductor 13 is expressed by the following equation (3), where V _f is the potential of the crystal upper surface electrode 15 and V _b is the potential of the bias electrode 16 .

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

In measuring the voltage _Vo of the high-voltage conductor 13, the amount of charge Q causes a measurement error. Further, when the voltage V _o of the high voltage conductor 13 is a DC voltage, unless the potential V _b of the bias electrode 16 is controlled following the potential fluctuation of the high voltage conductor 13 , a DC electric field is generated inside the electro-optic crystal 11 . will be applied. The electrical resistance R of the electro-optic crystal 11 is finite, and electrical conduction occurs according to the applied electric field. Therefore, the potential V _f of the crystal top surface electrode 15 changes over time so as to become the same potential as the ground conductor 14. do. This attenuation time constant τ is represented by the product of the permittivity and resistivity of the electro-optic crystal 11 .

On the other hand, in the photovoltage sensor 3 according to the third embodiment, by controlling the potential _Vb of the bias electrode 16 and maintaining the internal electric field of the electro-optic crystal 11 at zero, the electricity through the electro-optic crystal 11 is Suppress conduction. The signal processing device 51 calculates the potential _Vf applied to the electro-optic crystal 11 based on the detection signal output from the detector 41, and when this value has a value other than zero, the bias power supply 53 is turned on. is used to vary the potential _Vb of the bias electrode 16, and the potential _Vf of the crystal upper surface electrode 15 is changed so that the internal electric field of the _electro -optic crystal 11 is always zero. feedback control. The cycle of feedback control is set to a time sufficiently shorter than the time constant τ of electrical conduction of the electro-optic crystal 11 . Equation (3) is given by Equation (4) when the potential _Vf 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 of the bias electrode 16 (that is, the bias voltage) Vb. 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 _Vb that is the control voltage of the bias power supply 53 based on the equation (4), and outputs it to the output device 52 .

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

On the other hand, depending on the circumstances of the high voltage equipment in which the optical voltage sensor 3 according to Embodiment 3 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 if the distance between the high-voltage conductor 13 and the ground conductor 14 can be shortened, if a high voltage above a certain level is applied to the crystal top electrode 15, the crystal top electrode 15 will be charged. It causes deterioration of measurement accuracy. Therefore, in order to prevent the crystal upper surface electrode 15 from being charged, it is necessary to separate the high-voltage conductor 13 and the electro-optic crystal 11 by a distance that does not cause charging. In these cases, the voltage value applied to the electro-optic crystal 11 is reduced, and it becomes difficult to ensure measurement accuracy when adopting the vertical modulation method in which the sensitivity to voltage cannot be set high. On the other hand, in the optical voltage sensor 3 according to Embodiment 3, by adopting the horizontal modulation method, the shape of the electro-optic crystal 11 (for example, path length L and thickness D) By changing , 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 ensure measurement accuracy.

Further, as shown in FIG. 7A, when the horizontal modulation method of the comparative example in which the light is partially transmitted through the electro-optic crystal 11 is adopted, the laser light is generated even in the state where no voltage is applied to the electro-optic crystal 11. Due to the effects of light, temperature changes, etc., space charges move and output drift occurs, making it difficult to measure a DC voltage accurately and stably for a long period of time. In the photovoltage sensor 3 according to the third embodiment, as shown in FIG. 7B, the electro-optic crystal 11 receives light having a beam width W whose beam size is equal to or greater than the distance D between the first and second electrodes 12a and 12b. is incident, output drift can be avoided, and highly accurate and stable voltage measurement can be performed for a long period of time.

Except for the above, Embodiment 3 is the same as

Embodiment

1 or 2. Also, 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.
The configuration shown in the above embodiment shows an example of the content of the present disclosure, and can be combined with another known technology. It is also possible to omit or change the part.

1, 1a, 1b, 1c, 2, 3 optical voltage sensor, 10, 10a voltage application section, 11 electro-optic crystal, 11a, 11b end face, 12 electrode pair, 12a first electrode, 12b second electrode, 13 height voltage conductor, 14 ground conductor, 15 crystal upper surface electrode, 16 bias electrode, 20, 20a light projection unit, 21 light source, 211 array light source, 22 beam shaping optical system, 221 collimator lens, 222 beam shaper, 223 mask, 224 lens array , 30 polarization control optical system, 31 polarizer, 32 wavelength plate, 33 analyzer, 40, 40a light receiving section, 41 detector, 411 array detector, 42 lens, 43 mask, 50 signal processing section, 51 signal processing device, 52 Output device, 53 Bias power supply.

Claims

a light source;
an electro-optic crystal on which light emitted from the light source is incident;
a first electrode and a second electrode respectively provided on end faces of the electro-optic crystal facing each other, and applying an electric field to the electro-optic crystal in a direction perpendicular to the traveling direction of the light in the electro-optic crystal; an electrode pair to be applied;
a detector that receives the light emitted from the electro-optic crystal and outputs a detection signal based on the received light;
with
A photovoltage sensor, wherein the beam size of the light in the vertical direction at the time of incidence on the electro-optic crystal is equal to or greater than the distance between the first electrode and the second electrode.
2. The optical voltage sensor according to claim 1, wherein the first electrode and the second electrode are in close contact with the end surface of the electro-optic crystal.
3. The optical voltage sensor according to claim 1, 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 section that calculates the voltage applied to the electrode pair based on the detection signal.
5. The signal processing unit according to claim 4, wherein the signal processing unit calculates the voltage by excluding signal components based on light not incident on the electro-optic crystal from the detection signal output from the detector. optical voltage sensor.
6. The optical voltage sensor according to claim 4, wherein the signal processing unit performs processing for equalizing the vertical intensity distribution of the detection signal output from the detector.
a high voltage conductor spaced from the electro-optic crystal;
a bias electrode positioned between the first electrode and the high voltage conductor and spaced from the electro-optic crystal and the high voltage conductor;
a bias power supply that applies a bias potential to the bias electrode;
a signal processing unit that determines the bias potential based on the detection signal output from the detector;
further comprising
The optical voltage sensor according to any one of claims 1 to 3, wherein the signal processor calculates the potential of the high voltage conductor.
8. The photovoltage sensor according to claim 7, wherein the signal processing section controls the bias potential so as to keep the vertical electric field applied to the electro-optic crystal zero.
9. The device according to any one of claims 1 to 8, further comprising a first mask arranged between the light source and the electro-optic crystal and blocking part of the light emitted from the light source. An optical voltage sensor as described.
10. The detector according to any one of claims 1 to 9, further comprising a second mask disposed between said electro-optic crystal and said detector for blocking part of said light emitted from said electro-optic crystal. 2. The optical voltage sensor according to item 1.
11. The photovoltage according to any one of claims 1 to 10, further comprising a shaping optical system for uniformizing the vertical intensity distribution of the light at the time of incidence on the electro-optic crystal. sensor.
a polarizer and a wave plate for controlling the polarization state of the light upstream of the electro-optic crystal;
an analyzer for controlling the polarization state of light emitted from the electro-optic crystal;
12. The optical voltage sensor of any one of claims 1-11, further comprising:
The optical voltage sensor according to any one of claims 1 to 12, wherein the light source is an array light source in which a plurality of light emitting elements are arranged one-dimensionally or two-dimensionally.