Voltage measuring device

Abstract

To obtain a voltage measuring device capable of precisely measuring voltage even if a sharp voltage is applied.SOLUTION: A voltage measuring device 1 includes: a sensor part 10 that has a first end face, and a second end face directed to the opposite side of the first end face, and includes an electrooptical crystal for generating a phase difference corresponding to strength of an electric field operating between the fist end face and the second end face in two polarization components of light propagated between the first end face and the second end face; and a signal processing part 30 that obtains voltage applied to a high-voltage conductor 11 on the basis of light in which a polarization state is changed by propagation between the first end face and the second end face. The sensor part 10 includes: a contact type electrooptical crystal 13 in which the first end face abuts on the high-voltage conductor 11 and the second end face abuts on a ground conductor 12; and a non-contact type electrooptical crystal 14 that has a relation in which the first end face comes into contact with the high-voltage conductor 11 and the second end face does not come into contact with the ground conductor 12 or has a relation in which the second end face electrically comes into contact with the ground conductor 12 and the first end face does not come into contact with the high-voltage conductor 11.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a voltage measurement device that measures voltage using the electro-optic effect. [Background technology]

[0002] High-voltage direct current (HVDC) systems have attracted attention as a type of long-distance power transmission system due to their high transmission efficiency. DC voltages are constantly monitored by AC / DC converters, which are connected to DC and AC transmission systems to convert AC power to DC power, and by frequency converters, which are connected to AC transmission systems to convert voltage frequencies. Because the system voltages monitored are high, on the order of several hundred kV, a known technique is to use a voltage divider to reduce the system voltage to a more manageable level and then measure the reduced voltage with a voltage measuring device.

[0003] Furthermore, a voltage measuring device utilizing the Pockels effect, a first-order electro-optic effect, has been developed as a method for measuring high voltages without using a voltage divider. The Pockels effect is a phenomenon in which the refractive index of a certain type of crystal known as an electro-optic crystal changes in proportion to the strength of the electric field when an electric field is applied to the crystal. Although the change in the refractive index of a crystal due to the Pockels effect is small, it can be measured as a change in the polarization state of transmitted light by utilizing the anisotropy that occurs in the refractive index. For example, the voltage applied to the electro-optic crystal can be determined by using a polarizing element to introduce linearly polarized light into the electro-optic crystal and measuring the change in the polarization state of the light exiting the electro-optic crystal as a change in light intensity.

[0004] Voltage measurement devices using the Pockels effect have the advantages of excellent insulation and the ability to achieve compact size and low cost. However, when a DC voltage is applied to an electro-optic crystal, the space charge within the crystal shifts over time, changing the electric field distribution in the light-transmitting portion, making it difficult to measure voltage stably over long periods of time. To avoid this effect, a vertical modulation method has been proposed, in which the direction of light propagation and the direction of the applied electric field are aligned within the electro-optic crystal (see, for example, Patent Document 1). With the vertical modulation method, even if the electric field distribution within the electro-optic crystal becomes uneven due to the application of a DC voltage, light passes through both the areas where the electric field is strengthened and the areas where the electric field is weakened, and the integral value along the electric field direction remains constant, allowing for stable measurement of the voltage applied between the end faces of the electro-optic crystal. However, if the electrode to which the voltage to be measured is applied and the electro-optic crystal are not in close contact, the resistance of the gap becomes significant compared to the resistance of the electro-optic crystal, making it difficult to stably measure DC voltages over long periods of time. Therefore, optical voltage measurement devices for DC measurement require a configuration in which the electro-optic crystal is in close contact with the electrodes. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-11019 Summary of the Invention [Problem to be solved by the invention]

[0006] In a voltage measurement device using the Pockels effect, when an electro-optic crystal is attached to an electrode to stably measure DC voltage for a long period of time, if a voltage with a steep change is applied to the electro-optic crystal, a noise component is superimposed on the measurement signal due to the electrostrictive effect of the electro-optic crystal, and an accurate voltage cannot be measured. The electrostrictive effect, also known as the inverse piezoelectric effect, is a phenomenon in which mechanical distortion occurs due to polarization when an electric field is applied to an electro-optic crystal, causing the crystal to vibrate in an eigenmode in the direction of the electric field and perpendicular to the electric field.

[0007] The present disclosure has been made in view of the above, and has an object to provide a voltage measuring device that can measure voltage with high accuracy even when a steep voltage is applied. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, a voltage measurement device according to the present disclosure has a first end face facing a high-voltage conductor having the same potential as an object to be measured, and a second end face facing a ground conductor on the opposite side to the first end face, The light is incident from the second end face, 1st end face Reflected by 2nd end face Route back to a sensor unit including a plurality of electro-optic crystals that generate a phase difference in two polarized components of light propagating through the sensor, the two polarized components having mutually orthogonal vibration directions, according to the strength of the electric field acting between the first end face and the second end face; and Light is incident on the second end face, and electro-optical crystal The second end face of A component contained in light emitted from route and a signal processing unit that determines a voltage applied to the high-voltage conductor based on signals detected by each of the plurality of photodetectors corresponding to the plurality of electro-optic crystals. The sensor unit includes a contact electro-optic crystal having a first end face in electrical contact with the high-voltage conductor and a second end face in electrical contact with a ground conductor, and a non-contact electro-optic crystal having a first end face in electrical contact with the high-voltage conductor and a second end face in electrical non-contact with the ground conductor, or a non-contact electro-optic crystal having a second end face in electrical contact with the ground conductor and a first end face in electrical non-contact with the high-voltage conductor. When a steep voltage is applied to the high-voltage conductor, the signal processing unit determines the voltage applied to the high-voltage conductor based on a signal detected by a photodetector corresponding to the non-contact electro-optic crystal until the influence of the electrostrictive effect of the contact electro-optic crystal subsides. do. [Effects of the Invention]

[0009] The present disclosure provides an advantage in that it is possible to realize a voltage measuring device that can measure voltage with high accuracy even when a steep voltage is applied. [Brief explanation of the drawings]

[0010] [Figure 1]FIG. 1 is a diagram showing a configuration example of a voltage measurement device according to a first embodiment; [Figure 2] FIG. 1 is a diagram showing a first example of a thin film that is brought into close contact with a first end face and a second end face of a contact electro-optic crystal according to a first embodiment; [Figure 3] FIG. 10 is a diagram showing a second example of a thin film that is brought into close contact with the first end face and the second end face of the contact electro-optic crystal according to the first embodiment. [Figure 4] FIG. 1 is a diagram showing a first example of a thin film that is brought into close contact with a first end face and a second end face of a non-contact electro-optic crystal according to a first embodiment. [Figure 5] FIG. 10 is a diagram showing a second example of a thin film that is brought into close contact with the first end face and the second end face of the non-contact electro-optic crystal according to the first embodiment. [Figure 6] FIG. 10 is a diagram showing a third example of a thin film that is brought into close contact with the first end face and the second end face of the non-contact electro-optic crystal according to the first embodiment. [Figure 7] FIG. 1 is a diagram showing an example of the shape of a non-contact electro-optic crystal according to the first embodiment; [Figure 8] FIG. 1 is a diagram showing an example of an electric field relaxation electrode provided on the top of a non-contact electro-optic crystal according to the first embodiment; [Figure 9] FIG. 1 is a diagram showing an example of the relationship between the light source, the photodetector, the polarization modulator, the polarizer, and the analyzer of the voltage measuring device according to the first embodiment and the polarization state of light. [Figure 10] FIG. 1 is a diagram showing an example of the relationship between a monitor signal of a drive voltage of a polarization modulator constituting the voltage measurement device according to the first embodiment and a light-receiving signal of a photodetector; [Figure 11] FIG. 1 is a diagram for explaining the effect of a Faraday rotator that constitutes the voltage measuring device according to the first embodiment. [Figure 12] FIG. 10 is a diagram showing an example of a change in measured voltage over time when the voltage measuring device according to the first embodiment measures a DC voltage using a non-contact electro-optic crystal. [Figure 13] FIG. 10 is a diagram showing an example of the relationship between the monitor signal of the drive voltage of the polarization modulator and the light-receiving signal of the photodetector when a steep voltage is applied to the high-voltage conductor that constitutes the voltage measuring device according to the first embodiment; [Figure 14]1 is a flowchart showing an example of an operation of the voltage measurement circuit according to the first embodiment to measure a voltage applied to a high-voltage conductor. [Figure 15] FIG. 1 is a diagram showing an example of the relationship between the phase difference of a contact electro-optic crystal and the phase difference of a non-contact electro-optic crystal that constitutes the voltage measurement device according to the first embodiment. [Figure 16] FIG. 10 is a diagram showing an example of a change over time in a voltage measurement result when a steep voltage is applied to a high-voltage conductor that constitutes the voltage measuring device according to the first embodiment. [Figure 17] FIG. 10 is a diagram showing a configuration example of a voltage measurement device according to a second embodiment; [Figure 18] FIG. 10 is a diagram showing a first example of the crystal orientation of a contact-type electro-optic crystal that constitutes a voltage measurement device according to a second embodiment. [Figure 19] FIG. 10 is a diagram showing a second example of the crystal orientation of the contact electro-optic crystal that constitutes the voltage measurement device according to the second embodiment. [Figure 20] FIG. 10 is a diagram showing an example of the relationship between the phase differences of two contact-type electro-optic crystals that constitute the voltage measurement device according to the second embodiment. [Figure 21] 10 is a flowchart showing an example of an operation of the voltage measurement circuit according to the second embodiment to measure a voltage applied to a high-voltage conductor. [Figure 22] A diagram showing an example of hardware for implementing a voltage measurement circuit. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a voltage measuring device according to an embodiment of the present disclosure will be described in detail with reference to the drawings.

[0012] Embodiment 1 FIG. 1 is a diagram illustrating an example of the configuration of a voltage measuring device 1 according to a first embodiment. The voltage measuring device 1 according to the first embodiment measures the voltage of a measurement target such as a power transmission system, an AC / DC converter, or a frequency converter. The voltage measuring device 1 according to the first embodiment includes a sensor unit 10, a light emitting / receiving unit 20, and a signal processing unit 30. The sensor unit 10 and the light emitting / receiving unit 20 are connected by an optical fiber 40. The optical fiber 40 is a polarization-maintaining fiber, that is, a fiber that utilizes the photoelastic effect or a structural change to generate birefringence in which the effective refractive index differs in two orthogonal axial directions of the core, thereby improving the polarization-maintaining characteristics of the transmitted light.

[0013] The sensor unit 10 includes a high-voltage conductor 11, a ground conductor 12, a contact electro-optic crystal 13 which is an electro-optic crystal in electrical contact with both the high-voltage conductor 11 and the ground conductor 12, a non-contact electro-optic crystal 14 which is an electro-optic crystal in electrical contact with one of the high-voltage conductor 11 and the ground conductor 12 but not with the other, a Faraday rotator 15, and a collimator lens 16. Note that FIG. 1 shows an example in which the non-contact electro-optic crystal 14 is in electrical contact only with the ground conductor 12 but not with the high-voltage conductor 11. Furthermore, as will be described in detail later, the contact electro-optic crystal 13 and the non-contact electro-optic crystal 14 are electro-optic crystals having a flat surface on which a conductive thin film is formed by vapor deposition or the like, and when the thin film formed on the flat surface is in close contact with the conductor (high-voltage conductor 11, ground conductor 12), the electro-optic crystal and the conductor are considered to be in "electrical contact."

[0014] The high-voltage conductor 11 is a conductor having the same potential as the voltage V to be measured. The voltage to be measured is a high voltage of several hundred kV. The ground conductor 12 is a conductor connected to a reference potential point.

[0015] The contact electro-optic crystal 13 and the non-contact electro-optic crystal 14 are crystals that exhibit the Pockels effect, a first-order electro-optic effect. The Pockels effect is a phenomenon in which the polarization state of an electro-optic crystal changes when an external electric field is applied, causing the refractive index to change in proportion to the strength of the electric field. Applying an external electric field in a specific direction to an electro-optic crystal causes anisotropy in the refractive index of the electro-optic crystal. Light is generally expressed as a combination of two polarized components whose vibration directions are perpendicular to each other. When light passes through an electro-optic crystal with anisotropic refractive index, a phase difference, i.e., a polarization phase difference, occurs between the two polarized components. In the Pockels effect, the polarization phase difference is proportional to the strength of the electric field applied to the electro-optic crystal. Therefore, the voltage applied to the electro-optic crystal can be determined by using a polarizing element to measure the change in the polarization state of light passing through the electro-optic crystal. Examples of crystals having the Pockels effect that can be used as the contact electro-optic crystal 13 and the non-contact electro-optic crystal 14 include LiNbO3, LiTaO3, ADP (NH4H2PO4), KDP (H2PO4), SiO2 (quartz), Bi 12 SiO 20 , Bi 12 GeO 20 , Bi4Ge3O 12 , ZnS, ZnTe, etc.

[0016] In the following description, of the end faces of the contact electro-optic crystal 13 and the non-contact electro-optic crystal 14, the end face facing the high-voltage conductor 11 may be referred to as the first end face, and the end face facing the ground conductor 12 may be referred to as the second end face. The second end face is the end face opposite to the first end face, and is electrically connected to the ground conductor 12. The direction of propagation of light incident on the contact electro-optic crystal 13 and the non-contact electro-optic crystal 14 is the same as the direction of the electric field applied to the contact electro-optic crystal 13 and the non-contact electro-optic crystal 14 (longitudinal modulation method). In addition, in order to allow light to be incident on the contact electro-optic crystal 13 and the non-contact electro-optic crystal 14 from the ground conductor 12 side, a hole (hereinafter sometimes referred to as a transmission hole) that transmits light is provided in the ground conductor 12. Light enters the second end face of each of the contact electro-optic crystal 13 and the non-contact electro-optic crystal 14 through a transmission hole provided in the ground conductor 12, is reflected by a mirror provided on the first end face side, and then exits from the second end face and the transmission hole in the ground conductor 12.

[0017] The contact electro-optic crystal 13 serves to measure the voltage V applied to the high-voltage conductor 11, except when a steep voltage is applied to the high-voltage conductor 11, causing the electrostrictive effect. If there is a spatial gap between the contact electro-optic crystal 13 and the high-voltage conductor 11 or between the contact electro-optic crystal 13 and the ground conductor 12, the measured voltage V is divided by the contact electro-optic crystal 13 and the spatial gap, making it difficult to accurately measure the DC voltage. Therefore, as shown in FIG. 2 , conductive thin films 13a and 13b are formed by vapor deposition or sputtering on the first and second end faces of the contact electro-optic crystal 13. The thin film 13a, which is in close contact with the first end face of the contact electro-optic crystal 13, is a metal film that acts as a mirror to reflect light. For example, aluminum (Al), gold (Au), silver (Ag), or copper (Cu) can be used. The thin film 13b, which is in close contact with the second end face of the contact electro-optic crystal 13, must be light-transmitting and can be a transparent electrode film. 3, in order to prevent light from being reflected at the second end face of contact electro-optic crystal 13, thin film 13b may be formed on the second end face excluding the region through which light passes (in the example shown in FIG. 3, the central portion of the second end face), and thin film 13c that prevents light from being reflected at the end face may be provided in the region through which light passes. Thin film 13c may be, for example, a single-layer or multi-layer dielectric film designed to suppress reflected light of the wavelength of light incident on contact electro-optic crystal 13.

[0018] Non-contact electro-optic crystal 14 serves to measure voltage V applied to high-voltage conductor 11 in place of contact electro-optic crystal 13 when a steep voltage is applied to high-voltage conductor 11 and contact electro-optic crystal 13 is affected by the electrostrictive effect. When a steep high voltage is applied to the electro-optic crystal, noise components are superimposed on the measurement signal due to the electrostrictive effect of the electro-optic crystal, making it difficult to measure the correct voltage. Since the effect of the electrostrictive effect increases as the voltage applied to the electro-optic crystal increases, the effect of the electrostrictive effect can be mitigated by lowering the voltage applied to the electro-optic crystal. For this reason, non-contact electro-optic crystal 14 is designed so that the voltage applied to the electro-optic crystal is sufficiently smaller than that of contact electro-optic crystal 13. 1, the length of non-contact electro-optic crystal 14 in the electric field direction, i.e., the distance from the first end face to the second end face, is set shorter than that of contact electro-optic crystal 13, and the first end face of non-contact electro-optic crystal 14 is physically separated from high-voltage conductor 11 so as to be electrically out of contact. Here, it is assumed that the length of non-contact electro-optic crystal 14 in the electric field direction is about one-tenth the length of contact electro-optic crystal 13 in the electric field direction. In this case, the voltage to be measured is divided by the spatial gap between non-contact electro-optic crystal 14 and high-voltage conductor 11, so the voltage applied to non-contact electro-optic crystal 14 is sufficiently smaller than that applied to contact electro-optic crystal 13. As a result, even when a steep high voltage is applied to high-voltage conductor 11, the correct voltage can be measured without being affected by the electrostrictive effect.

[0019] As shown in FIG. 4, thin films 14a and 14b are formed by vapor deposition or sputtering on the first and second end faces of non-contact electro-optic crystal 14. Thin film 14a, which is adhered to the first end face of non-contact electro-optic crystal 14, functions as a mirror for reflecting light. For example, a metal film such as aluminum (Al), gold (Au), silver (Ag), or copper (Cu) may be used. Thin film 14a does not need to be conductive and may be a mirror composed of a dielectric multilayer film. Thin film 14b, which is adhered to the second end face of non-contact electro-optic crystal 14, must transmit light and may be a transparent electrode film. As shown in FIG. 5, to prevent light from being reflected at the second end face of non-contact electro-optic crystal 14, thin film 14b may be formed on the portion of the second end face excluding the area through which light passes (in the example shown in FIG. 5, the central portion of the second end face). A thin film 14c that prevents light from being reflected at the end face may be provided in the light-passing area. Thin film 14c can be, for example, a single-layer or multi-layer dielectric film designed to suppress reflected light of the wavelength of light incident on non-contact electro-optic crystal 14. Furthermore, the thin film that adheres to the second end face does not need to be conductive, and may be composed of thin film 14c alone, as shown in FIG.

[0020] It is known that the influence of the electrostrictive effect depends on the shape of the end faces of the electro-optic crystal. Therefore, the non-contact electro-optic crystal 14 has a first end face and a second end face as shown in FIG. Size The influence of the electrostrictive effect may be reduced by changing the size of the field relaxation electrode 17 to form a tapered shape. Furthermore, as shown in Fig. 8, a field relaxation electrode 17 may be provided on the top of non-contact electro-optic crystal 14, i.e., on the side of the first end face, to relax the electric field concentration at the edge portion of the first end face. By providing field relaxation electrode 17 on the top of non-contact electro-optic crystal 14 in this way, and changing the size of field relaxation electrode 17, the voltage applied to non-contact electro-optic crystal 14 can be adjusted.

[0021] The Faraday rotator 15 is a rotator that rotates the plane of polarization of incident light by the Faraday effect. The Faraday effect is a phenomenon in which, when a magnetic field is applied parallel to the direction of light propagation, the plane of polarization rotates in accordance with the strength of the magnetic field. Generally, it is difficult to transmit light through the optical fiber 40 while maintaining its phase state. However, by using the Faraday rotator 15, which is designed to rotate the plane of polarization of incident light by 45 degrees, and passing the light back and forth through the optical fiber 40, it is possible to transmit the light while maintaining its phase state.

[0022] The collimator lens 16 serves to convert the light emitted from the optical fiber 40 into parallel light, and further serves to reflect the light that is reflected back at the first end face of each of the contact electro-optic crystal 13 and the non-contact electro-optic crystal 14 back into the optical fiber 40.

[0023] The light projecting and receiving unit 20 includes a light source 21, photodetectors 22a, 22b, and 22c, a polarization modulator 23, a polarizer 24, analyzers 25a, 25b, and 25c, beam splitters 26a, 26b, and 26c, and a collimator lens 27.

[0024] The light source 21 may be a light-emitting diode (LED), a semiconductor laser, a solid-state laser, or a gas laser. The light emitted from the light source 21 is preferably infrared light with a wavelength of 750 nm or longer, which is light with a long enough wavelength not to cause an internal photoelectric effect. The internal photoelectric effect is a phenomenon in which irradiation with short-wavelength light reduces the electrical resistance of an insulator, making it easier for current to flow. Furthermore, since light travels back and forth within the optical fiber 40, it is preferable to use a light source with low coherence, such as an LED, an SLD (Super Luminescent Diode), or an ASE (Amplified Spontaneous Emission).

[0025] Photodetectors 22a, 22b, and 22c detect the light intensity as an electrical signal through optical-to-electrical conversion (O / E conversion). Photodetectors 22a, 22b, and 22c can be, for example, photodiodes that have high sensitivity to the wavelength of light emitted by light source 21. Photodetector 22a is used to measure the polarization state of light emitted from polarization modulator 23. Photodetector 22b is used to measure the polarization state of light that has traveled back and forth within contact electro-optic crystal 13. Photodetector 22c is used to measure the polarization state of light that has traveled back and forth within non-contact electro-optic crystal 14.

[0026] The polarization modulator 23 is an optical element that modulates the polarization state of transmitted light. Examples of polarization modulators that can be used include electro-optical element modulators and piezoelectric element modulators configured by wrapping optical fiber around a cylindrical piezoelectric element. The polarization modulator 23 imparts a phase difference between two orthogonal polarization components by applying an external voltage to the electro-optical element or cylindrical piezoelectric element. When the incident light to the polarization modulator 23 is linearly polarized, the output light is the same linearly polarized light as the incident light when a voltage that results in a phase difference of 0 is applied, circularly polarized when a voltage that results in a phase difference of λ / 4 is applied, and linearly polarized light rotated 90 degrees relative to the linearly polarized light of the incident light when a voltage that results in a phase difference of λ / 2 is applied.

[0027] The polarizer 24 is an optical element disposed between the light source 21 and the polarization modulator 23, and converts the light emitted from the light source 21 into linearly polarized light. The analyzers 25a, 25b, and 25c are optical elements disposed in front of the photodetectors 22a, 22b, and 22c, respectively, and extract linearly polarized light from the transmitted light.

[0028] Beam splitters 26a, 26b, and 26c are polarization-independent beam splitters that are optical elements that split the transmitted light and reflected light at a predetermined light intensity ratio without changing the polarization state of the incident light. Beam splitter 26a is located after polarization modulator 23 and serves to split the light emitted by polarization modulator 23 into light that is incident on photodetector 22a and light that is incident on contact electro-optic crystal 13 or non-contact electro-optic crystal 14. Beam splitter 26b is located after beam splitter 26a when viewed from the light source 21 side and serves to split the light emitted by polarization modulator 23 into light that is incident on contact electro-optic crystal 13 and light that is incident on non-contact electro-optic crystal 14, and serves to direct the light returned from contact electro-optic crystal 13 to photodetector 22b. Beam splitter 26c is positioned after beam splitter 26b when viewed from the light source 21 side, and serves to direct the light emitted by polarization modulator 23 to the non-contact electro-optic crystal 14 and direct the light returned from the non-contact electro-optic crystal 14 to the photodetector 22c.

[0029] The collimator lens 27 allows the light reflected in a 90-degree direction by the beam splitter 26b or the beam splitter 26c to enter the optical fiber 40, and then passes through the sensor unit 10 to convert the light emitted from the optical fiber 40 into parallel light, which is then incident on the photodetector 22b or the photodetector 22c.

[0030] The signal processing unit 30 includes a modulator driving circuit 31 and a voltage measurement circuit 32. The modulator driving circuit 31 outputs a driving voltage for operating the polarization modulator 23 and outputs a monitor signal for the driving voltage to the voltage measurement circuit 32. The voltage measurement circuit 32 calculates the voltage V applied to the high-voltage conductor 11 based on the light-receiving signals of the photodetectors 22a, 22b, and 22c and the monitor signal for the driving voltage of the polarization modulator 23. The voltage measurement circuit 32 converts the calculated voltage V using a predetermined voltage division ratio and outputs it as an analog or digital value. The voltage measurement circuit 32 may also display the calculated voltage V in analog or digital form using a display not shown in FIG. 1.

[0031] The operation of the voltage measuring device 1 according to the first embodiment will be described below. Light emitted from the light source 21 is incident on the polarizer 24. The polarizer 24 extracts linearly polarized light from the incident light. The linearly polarized light extracted by the polarizer 24 is incident on the polarization modulator 23. The polarization modulator 23 converts the incident linearly polarized light into elliptically polarized light or circularly polarized light according to the drive voltage output from the modulator drive circuit 31. The light emitted from the polarization modulator 23 is split by the beam splitter 26a into transmitted light and light reflected in a 90-degree direction, and the light reflected in a 90-degree direction is incident on the analyzer 25a. The analyzer 25a extracts linearly polarized light from the incident light. The linearly polarized light extracted by the analyzer 25a is incident on the photodetector 22a.

[0032] 9 is a diagram showing an example of the relationship between the light source 21, the photodetectors 22a, 22b, and 22c, the polarization modulator 23, the polarizer 24, and the analyzers 25a, 25b, and 25c and the polarization state of light. The polarization modulator 23 is a modulator using an electro-optic crystal, and is driven by a driving voltage V EO When a voltage V is applied, EO It is assumed that a refractive index difference, i.e., a polarization phase difference θ, occurs in the direction perpendicular to the axis (electric field direction) of the electro-optic crystal (here, X direction) and in the direction parallel to the axis (electric field direction) of the electro-optic crystal in proportion to I. As shown in FIG. 9, the polarizer 24 and the analyzer 25a are arranged so that the linearly polarized light that passes through them is oriented at 45 degrees to the crystal axis (electric field direction) of the polarization modulator 23. The amount of light incident on the polarization modulator 23 is expressed as I. in The amount of light emitted from the polarization modulator 23 and detected by the photodetector 22a via the analyzer 25a is I out Then, I out / I in is expressed by the following equation (1).

[0033]

number

[0034] The polarization phase difference θ is determined by the driving voltage V of the polarization modulator 23. EO , the driving voltage V of the polarization modulator 23 is proportional to EOThe light receiving signal of the photodetector 22a in response to the monitor signal can be expressed as the solid line in FIG.

[0035] Light emitted from polarization modulator 23 and transmitted through beam splitter 26a is split by beam splitter 26b into light that transmits and light that is reflected in a 90-degree direction. The light reflected in the 90-degree direction is focused into optical fiber 40 by collimator lens 27. The light focused into optical fiber 40 is transmitted to sensor unit 10, emitted from collimator lens 16 of sensor unit 10, and incident on Faraday rotator 15. Faraday rotator 15 rotates the plane of polarization of the incident light by 45 degrees. The light emitted from Faraday rotator 15 enters contact electro-optic crystal 13 from the second end face, is reflected by thin film 13a that functions as a mirror and is provided on the first end face, and exits from the second end face. The light that exits from the second end face of contact electro-optic crystal 13 enters Faraday rotator 15 again. The Faraday rotator 15 rotates the plane of polarization of the incident light by 45 degrees, thereby rotating the plane of polarization of the light by 90 degrees on both the outbound and return journeys. The light emitted from the Faraday rotator 15 is focused into an optical fiber 40 by a collimator lens 16. The light focused into the optical fiber 40 is transmitted to the light projecting and receiving unit 20.

[0036] Here, the principle of phase noise cancellation by the Faraday rotator 15 will be explained using FIG. 11. Assume that linearly polarized light is incident at an angle of 45 degrees with respect to the eigenaxis of the polarization-maintaining fiber. The linearly polarized light is separated into orthogonal polarization components in the X-axis and Y-axis directions, and the phases of the polarization components are respectively φ x and φ y Generally, when light propagates through an optical fiber, disturbances such as bending of the fiber and temperature changes cause phase noise n x and n y When light emitted from an optical fiber is reflected directly by a mirror, the phase after passing through the optical fiber again is φ x +2n x and φ y +2n y In other words, the phase difference Δ between orthogonal polarized light beams traveling back and forth through the optical fiber is expressed by the following equation (2), and is 2n x-2n y is the phase noise due to the optical fiber.

[0037]

number

[0038] 11, when a Faraday rotator 15 capable of rotating the polarization plane by 45 degrees is inserted, the polarization plane of the light emitted from the optical fiber 40 is rotated by 90 degrees and the orthogonal polarization components are swapped as it travels back and forth through the Faraday rotator 15. In other words, after traveling back and forth through the optical fiber 40, each polarization component has a phase noise n x +n y The phase difference Δ between the orthogonal polarized lights at this time is expressed by the following equation (3), and the phase noise n x and n y is removed.

[0039]

number

[0040] Returning to the explanation of the operation of the voltage measuring device 1, the light that travels back and forth within the contact-type electro-optic crystal 13 of the sensor unit 10 and is transmitted to the light projecting and receiving unit 20 via the optical fiber 40 is converted into parallel light by the collimator lens 27, passes through the beam splitter 26b and the analyzer 25b, and is then detected by the photodetector 22b. As shown in FIG. 9, the analyzer 25b is positioned so that the linearly polarized light that passes through it is oriented at 45 degrees to the axis (electric field direction) of the electro-optic crystal of the polarization modulator 23. The driving voltage V of the polarization modulator 23 EO The phase difference between the monitor signal of the photodetector 22b and the photodetector 22a is θ 13 10. In the following, it is assumed that there is no natural birefringence in all optical elements through which light passes, including the contact electro-optic crystal 13, and that the time delay of light due to the optical path length can be ignored. When the voltage V of the high-voltage conductor 11 is zero, the phase of the light-receiving signal of the photodetector 22b becomes the same as the phase of the light-receiving signal of the photodetector 22a, and the phase difference θ 13becomes zero.

[0041] When a voltage V is applied to the high-voltage conductor 11, the high-voltage conductor 11 and the ground conductor 12 are electrically connected to the thin film 13a in close contact with the first end face of the contact electro-optic crystal 13 and the thin film 13b in close contact with the second end face thereof, respectively, and therefore the voltage V is applied to the contact electro-optic crystal 13. When the voltage V is applied to the contact electro-optic crystal 13, the refractive index difference in two directions orthogonal to the polarization plane of light, that is, the phase difference θ 13 The voltage measurement circuit 32 of the signal processing unit 30 measures the light reception signal of the photodetector 22a, the light reception signal of the photodetector 22b, and the drive voltage V output from the modulator drive circuit 31. EO Based on the monitor signal and the phase difference θ 13 Voltage measurement circuit 32 further calculates voltage V based on a proportionality constant A obtained in advance, using the relationship expressed by the following equation (4). The proportionality constant A depends on the Pockels coefficient of contact electro-optic crystal 13.

[0042]

number

[0043] Light emitted from polarization modulator 23 and transmitted through beam splitters 26a and 26b is reflected by beam splitter 26c in a 90-degree direction, and the light reflected in the 90-degree direction is focused into optical fiber 40 by collimator lens 27. The light focused into optical fiber 40 is transmitted to sensor unit 10, emitted from collimator lens 16 of sensor unit 10, and incident on Faraday rotator 15. Faraday rotator 15 rotates the plane of polarization of the incident light by 45 degrees. The light emitted from Faraday rotator 15 enters non-contact electro-optic crystal 14 from the second end face, is reflected by thin film 14a, which functions as a mirror and is provided on the first end face, and exits from the second end face. The light emitted from the second end face of non-contact electro-optic crystal 14 enters Faraday rotator 15 again. The Faraday rotator 15 rotates the plane of polarization of the incident light by 45 degrees, thereby rotating the plane of polarization of the light by 90 degrees on both the outbound and return journeys. The light emitted from the Faraday rotator 15 is focused into an optical fiber 40 by a collimator lens 16. The light focused into the optical fiber 40 is transmitted to the light projecting and receiving unit 20.

[0044] The light transmitted to the light projecting and receiving unit 20 via the optical fiber 40 is converted into parallel light by the collimator lens 27, passes through the beam splitter 26c and the analyzer 25c, and is then detected by the photodetector 22c. As shown in Figure 9, the analyzer 25c is positioned so that the linearly polarized light that passes through it is oriented at 45 degrees to the axis (electric field direction) of the electro-optic crystal of the polarization modulator 23. The driving voltage V of the polarization modulator 23 EO The light receiving signal of the photodetector 22c with respect to the monitor signal of the photodetector 22a has a phase difference of θ 14 10. In the following, it is assumed that there is no natural birefringence in all optical elements that have passed through, including the non-contact electro-optic crystal 14, and that the time delay of light due to the optical path length can be ignored. When the voltage V of the high-voltage conductor 11 is zero, the phase of the light reception signal of the photodetector 22c becomes the same as the phase of the light reception signal of the photodetector 22a, and the phase difference θ 14 becomes zero.

[0045] When voltage V is applied to high-voltage conductor 11, voltage V is divided in the spatial gap between non-contact electro-optic crystal 14 and high-voltage conductor 11, and voltage V' is applied to non-contact electro-optic crystal 14. When voltage V' is applied to non-contact electro-optic crystal 14, a refractive index difference, i.e., a phase difference θ 14 The voltage measurement circuit 32 of the signal processing unit 30 measures the light reception signal of the photodetector 22a, the light reception signal of the photodetector 22c, and the drive voltage V output from the modulator drive circuit 31. EO Based on the monitor signal and the phase difference θ 14 Voltage measurement circuit 32 further calculates voltage V' based on a proportionality constant B obtained in advance, using the relationship expressed by the following equation (5). The proportionality constant B depends on the Pockels coefficient of non-contact electro-optic crystal 14.

[0046]

number

[0047] When voltage V is applied to high-voltage conductor 11, voltage V' applied to non-contact electro-optic crystal 14 has a value obtained by dividing voltage V by a predetermined voltage division ratio C, as shown in the following equation (6).

[0048]

number

[0049] However, if the voltage V applied to the high-voltage conductor 11 is DC, the voltage V' applied to the non-contact electro-optic crystal 14 gradually decreases over time. Therefore, when the voltage V applied to the high-voltage conductor 11 is calculated using the above equations (5) and (6) using the non-contact electro-optic crystal 14, a discrepancy occurs between the measured voltage and the actually applied voltage V over time, as shown in Figure 12. The time constant by which the measured voltage decays relative to the correct voltage V depends primarily on the electrical characteristics of the non-contact electro-optic crystal 14, but is generally on the order of several seconds or more. Therefore, the non-contact electro-optic crystal 14 is used to measure changes in the voltage V applied to the high-voltage conductor 11 over a relatively short period of time. For example, the non-contact electro-optic crystal 14 is used to measure the voltage V over a period of less than one second. The change ΔV in the voltage V applied to the high-voltage conductor 11 can be calculated using the change ΔV' in the voltage V' calculated using the above equation (5) using the following equation (7):

[0050]

number

[0051] When a steep voltage exceeding 100 kV is applied to the high-voltage conductor 11 within 1 microsecond, for example, the electrostrictive effect causes noise components to be superimposed on the light-receiving signal of the photodetector 22b, as shown by the thick dashed line in Figure 13, making it difficult to accurately measure the voltage. The effect of the electrostrictive effect increases as the voltage applied to the electro-optic crystal increases. Therefore, the size of the non-contact electro-optic crystal 14 in the electric field direction is smaller than that of the contact electro-optic crystal 13, creating a spatial gap between the high-voltage conductor 11 and the electro-optic crystal. This allows the non-contact electro-optic crystal 14 to reduce the voltage applied to the electro-optic crystal compared to the contact electro-optic crystal 13, thereby suppressing the effect of the electrostrictive effect. For example, the size of the non-contact electro-optic crystal 14 in the electric field direction is designed so that even if the maximum expected voltage is instantaneously applied to the high-voltage conductor 11, the voltage actually applied to the non-contact electro-optic crystal 14 after being divided is large enough to sufficiently ignore the effect of the electrostrictive effect. As a result, even when a steep high voltage is applied to the high-voltage conductor 11, the non-contact electro-optic crystal 14 can measure the correct voltage without any noise components being superimposed on the light receiving signal of the photodetector 22c, as shown by the thin dashed line in Figure 13.

[0052] 14 is a flowchart showing an example of the operation of voltage measurement circuit 32 according to the first embodiment to measure voltage V applied to high-voltage conductor 11. In the operation of measuring voltage V shown in FIG. 14, voltage measurement circuit 32 first measures the light-receiving signals of photodetectors 22a, 22b, and 22c, and drive voltage V of polarization modulator 23 output from modulator drive circuit 31. EO and the phase difference θ of the contact-type electro-optic crystal 13 based on the monitor signal. 13 and the phase difference θ of the non-contact electro-optic crystal 14 14 is measured (step S11).

[0053] When the contact electro-optic crystal 13 and the non-contact electro-optic crystal 14 are the same type of crystal but differ only in size, i.e., when the lengths in the electric field direction are different, the half-wave voltage Vπ of the high-voltage conductor 11 at which the phase difference is π is larger for the non-contact electro-optic crystal 14 than for the contact electro-optic crystal 13. For example, the half-wave voltage V 14 π is 300 kV, and the half-wave voltage V of the contact electro-optic crystal 13 13 When π is 25 kV, the phase difference θ of the contact-type electro-optic crystal 13 13 and the phase difference θ of the non-contact electro-optic crystal 14 14 The relationship between the phase difference θ and the phase difference θ can be expressed as shown in FIG. 13 is 0≦θ 13 However, the non-contact electro-optic crystal 14 alone can measure the voltage V within the range of 0≦V<50 kV, where the phase difference θ 14 is 0≦θ 14 However, as described above, when the voltage V applied to the high-voltage conductor 11 is a DC voltage, the phase difference θ 14 As shown in FIG. 12, the voltage obtained from the voltage measurement will deviate from the correct voltage over time, and therefore non-contact electro-optic crystal 14 is used mainly to detect short-term voltage changes.

[0054] Next, the voltage measurement circuit 32 measures the phase difference θ 14 The phase change Δθ from the previous measurement value 14 Next, the voltage measurement circuit 32 calculates the phase change amount Δθ of the non-contact electro-optic crystal 14. 14 The threshold θ is set T It is checked whether the threshold θ is equal to or less than the threshold θ (step S13). T is determined based on the voltage change ΔV of the high voltage conductor 11 at which the influence of the electrostrictive effect of the contact electro-optic crystal 13 becomes negligible. For example, when ΔV is 50 kV, the half-wave voltage V of the non-contact electro-optic crystal 14 is 14 When π is 300 kV, the threshold θ T becomes 1 / 6π.

[0055] The voltage measurement circuit 32 measures the phase change amount Δθ of the non-contact electro-optic crystal 14. 14 is the threshold θ T In the following cases (step S13: Yes), the phase difference θ of the contact-type electro-optic crystal 13 is calculated using the above formula (4). 13 Based on this, the voltage V of the high voltage conductor 11 is calculated (step S14).

[0056] However, the phase difference θ of the contact-type electro-optic crystal 13 13 The measurable range is 0≦θ 13 <2π, and the voltage V applied to the high-voltage conductor 11 is 0≦V<2V 13 If it is outside the range of π[V], the phase difference θ 13 Therefore, the voltage measurement circuit 32 detects that the voltage V applied to the high-voltage conductor 11 is 0≦V<2V. 13 If it is outside the range of π [V], the phase change amount Δθ of the non-contact electro-optic crystal 14 compared with the previous measured voltage 14 The phase difference θ of the contact electro-optic crystal 13 is calculated using the information 13 For example, if the previous measured voltage is 25 kV (i.e., θ 13 =π), and the voltage change ΔV to the high-voltage conductor 11 is +25 kV, that is, when the voltage V changes from 25 kV to 50 kV, the phase difference θ of the contact-type electro-optic crystal 13 13 is either 0 or 2π, and it is not possible to determine whether the voltage V is 0 kV or 50 kV. In this case, the phase change amount Δθ of the non-contact electro-optic crystal 14 14 By utilizing the fact that the voltage V is −1 / 12π when it is 0 kV and +1 / 12π when it is 50 kV, it is estimated that the voltage V is 50 kV. In this way, the difference between the previously measured voltage and the phase change amount Δθ of the non-contact electro-optic crystal 14 is 14 By using the information of 14 -π≦Δθ 14 <π, that is, if the voltage change ΔV to the high-voltage conductor 11 is within the range of −300 kV≦ΔV<300 kV, it becomes possible to calculate the voltage V.

[0057] The voltage measurement circuit 32 measures the phase change amount Δθ of the non-contact electro-optic crystal 14. 14 is the threshold θ T If it is not equal to or less than the above (step S13: No), the phase difference θ 14 (Step S15). Specifically, voltage measurement circuit 32 first calculates the amount of phase change Δθ of non-contact electro-optic crystal 14 from the above equations (5) and (7). 14 The voltage measurement circuit 32 then calculates the voltage V of the high-voltage conductor 11 by adding the voltage change ΔV to the previously measured voltage.

[0058] Next, the voltage measurement circuit 32 measures the phase change amount Δθ of the non-contact electro-optic crystal 14. 14 is the threshold θ T (Step S16). Time T is the time when the influence of the electrostrictive effect on contact electro-optic crystal 13 can be ignored. That is, this time T is the time when the influence of the electrostrictive effect on contact electro-optic crystal 13 subsides after a steep high voltage is applied to high voltage conductor 11, and the phase difference θ of contact electro-optic crystal 13 13 This is the time it takes to be able to measure the correct voltage based on the

[0059] The voltage measurement circuit 32 measures the phase change Δθ 14 is the threshold θ T If the predetermined time T has not elapsed since the time T has exceeded the predetermined time T (step S16: No), the phase difference θ 14 (Step S17). Next, the voltage measurement circuit 32 returns to Step S15 and measures the phase difference θ 14 The voltage V of the high-voltage conductor 11 is calculated based on the above (step S15). 14 is the threshold θ T Steps S15 to S17 are repeated until a predetermined time T has elapsed since the voltage measurement circuit 32 exceeds the phase change amount Δθ 14 is the threshold θ TIf the predetermined time T has elapsed since the time T was exceeded (step S16: Yes), the process returns to step S11, and step S11 and the subsequent steps (processing of each step) are repeated.

[0060] 16 is a diagram showing an example of the time change in the voltage output by voltage measurement circuit 32 when a steep voltage V is applied to high-voltage conductor 11. In FIG. 16, black circles represent the phase difference θ 13 The white circle indicates the phase difference θ of the non-contact electro-optic crystal 14. 14 16, before a steep voltage is applied, the voltage measurement circuit 32 measures the phase difference θ 13 On the other hand, from immediately after the application of a steep voltage until the time T at which the influence of the electrostrictive effect of contact-type electro-optic crystal 13 can be ignored has elapsed, voltage measurement circuit 32 calculates and outputs the voltage V of high-voltage conductor 11 based on the phase difference θ 14 After the time T has elapsed in which the influence of the electrostrictive effect of contact electro-optic crystal 13 can be ignored, voltage measurement circuit 32 again calculates and outputs the phase difference θ 13 Based on this, the voltage V of high-voltage conductor 11 is calculated and output (operations shown in steps S11 to S14 in FIG. 14).

[0061] As described above, the voltage measuring device 1 according to the first embodiment includes contact electro-optic crystal 13, which is an electro-optic crystal in electrical contact with both high-voltage conductor 11, which is a conductor at the same potential as the voltage to be measured, and ground conductor 12, which is a conductor connected to a reference potential point, and non-contact electro-optic crystal 14, which is an electro-optic crystal in electrical contact with either high-voltage conductor 11 or ground conductor 12. During the period from when a steep voltage is applied to high-voltage conductor 11 until a predetermined time has elapsed, that is, until the influence of the electrostrictive effect of contact electro-optic crystal 13 becomes negligible, the phase difference θ 14After a predetermined time has elapsed, the voltage measuring device 1 calculates the voltage V of the high-voltage conductor 11 based on the phase difference θ 13 The voltage V of the high-voltage conductor 11 is calculated based on the above. The voltage measuring device 1 not only realizes DC measurement, but also can measure DC voltage with high accuracy even when a steep voltage is applied.

[0062] Embodiment 2 In the voltage measuring device 1 according to the first embodiment described above, before the voltage measuring circuit 32 starts measuring the voltage V applied to the high-voltage conductor 11, a direct current is applied to the high-voltage conductor 11 and 0≦V<2V 13 If a voltage V outside the range of π [V] is applied for a long period of time, it is not possible to measure the correct voltage. In the second embodiment, a voltage measuring device that can solve this problem and measure the correct voltage will be described.

[0063] In order to solve the above problem, the voltage measuring device 1a according to the second embodiment differs from the voltage measuring device 1 according to the first embodiment in that, in addition to the contact electro-optic crystal 13, it further includes another contact electro-optic crystal that is the same as the contact electro-optic crystal 13, i.e., an electro-optic crystal that is in electrical contact with both the high-voltage conductor 11 and the ground conductor 12. The half-wave voltage of the other contact electro-optic crystal is the half-wave voltage V of the contact electro-optic crystal 13. 13 The half-wave voltage of contact electro-optic crystal 13 is set to be different from the half-wave voltage of other contact electro-optic crystals, for example, by the following three methods.

[0064] (1) The contact electro-optic crystal 13 and the other contact electro-optic crystals are made of the same material, and the orientation in which the crystals are cut is changed. (2) The contact electro-optic crystal 13 and other contact electro-optic crystals are made of the same material, and light of different wavelengths is incident thereon. (3) The contact electro-optic crystal 13 and the other contact electro-optic crystals are made of different materials.

[0065] In this embodiment, a voltage measuring device configured to apply the above method (1) will be described as an example.

[0066] Fig. 17 is a diagram showing an example of the configuration of a voltage measuring device 1a according to embodiment 2. In Fig. 17, components common to the voltage measuring device 1 according to embodiment 1 shown in Fig. 1 are assigned the same reference numerals as in Fig. 1.

[0067] 17, the voltage measuring device 1a according to the second embodiment includes a sensor unit 101, a light emitting / receiving unit 201, and a signal processing unit 301. This voltage measuring device 1a has a configuration in which a contact electro-optic crystal 131, a Faraday rotator 15, a collimator lens 16, a photodetector 22d, an analyzer 25d, a beam splitter 26d, a collimator lens 27, and an optical fiber 40 are added to the voltage measuring device 1 according to the first embodiment.

[0068] In the voltage measuring device 1a, the sensor unit 101 has a configuration in which a contact electro-optic crystal 131, a Faraday rotator 15, and a collimator lens 16 are added to the sensor unit 10 of the voltage measuring device 1 according to the first embodiment. The light projecting and receiving unit 201 has a configuration in which a photodetector 22d, an analyzer 25d, a beam splitter 26d, and a collimator lens 27 are added to the light projecting and receiving unit 20 of the voltage measuring device 1 according to the first embodiment. Furthermore, the signal processing unit 301 has a configuration in which the voltage measurement circuit 32 of the signal processing unit 30 of the voltage measuring device 1 according to the first embodiment is replaced with a voltage measurement circuit 321. Note that the photodetector 22d, the analyzer 25d, and the beam splitter 26d are the same components as the photodetectors 22a, 22b, and 22c, the analyzers 25a, 25b, and 25c, and the beam splitters 26a, 26b, and 26c, respectively.

[0069] Like contact electro-optic crystal 13, contact electro-optic crystal 131 has a conductive thin film formed in close contact with the first and second end faces, and is in electrical contact with both ground conductor 12 and high-voltage conductor 11. Contact electro-optic crystals 13 and 131 are crystals made of the same material, but as shown in Figures 18 and 19, the half-wave voltage can be adjusted to different values ​​by changing the cutting method relative to the crystal axis. Figure 18 shows a method for cutting contact electro-optic crystal 13, and Figure 19 shows a method for cutting contact electro-optic crystal 131.

[0070] In the following, as an example, the contact-type electro-optic crystals 13 and 131 are made of Bi4Ge3O 12 The explanation will be given assuming that the wavelength of the light source is 850 nm and that the contact electro-optic crystal 13 is cut along the crystal axis

[0001] direction as shown in FIG. 18, whereas the contact electro-optic crystal 131 is cut at an angle of φ with respect to the crystal axis

[0001] as shown in FIG. 19. For example, φ=10 degrees. In this case, the half-wave voltage V of the contact electro-optic crystal 13 13 π is 25 kV, and the half-wave voltage V of the contact-type electro-optic crystal 131 131 π is 26.5 kV, and the half-wave voltage V of the contact-type electro-optic crystal 131 131 π is the half-wave voltage V of the contact-type electro-optic crystal 13 13 In this case, the range of voltage V that can be measured by the contact-type electro-optic crystal 13 alone is 0≦V<50 kV (=2 V 13 π), the range of voltage V that can be measured by the contact-type electro-optic crystal 131 alone is 0≦V<53kV (=2V 131 In this case, as shown in FIG. 20, the phase difference θ 13 and the phase difference θ of the contact-type electro-optic crystal 131 131 By utilizing this relationship, the measurement range of voltage V can be expanded beyond -400 kV≦V≦+400 kV. The measurable voltage range is determined by the ratio of the half-wavelength voltage of contact electro-optic crystal 13 to the half-wavelength voltage of contact electro-optic crystal 131. In other words, the measurable voltage range can be adjusted by changing the cut angle φ of contact electro-optic crystal 131.

[0071] 21 is a flowchart showing an example of the operation of voltage measurement circuit 321 according to embodiment 2 to measure voltage V applied to high-voltage conductor 11. The operation of voltage measurement circuit 321 to measure voltage V applied to high-voltage conductor 11 is partially different from the operation of voltage measurement circuit 32 according to embodiment 1 to measure voltage V applied to high-voltage conductor 11 (see FIG. 14). In FIG. 21, the same step numbers as in FIG. 14 are assigned to processes that are common to the operation of voltage measurement circuit 32 according to embodiment 1 shown in FIG. 14. Detailed description of the processes assigned the same step numbers as in FIG. 14 will be omitted.

[0072] In the operation of measuring the voltage V shown in FIG. 21, first, the voltage measurement circuit 321 measures the light receiving signals of the photodetectors 22a, 22b, 22c, and 22d, and the drive voltage V of the polarization modulator 23 output from the modulator drive circuit 31. EO Based on the monitor signal, the phase difference θ of each of the contact-type electro-optic crystals 13 and 131 is calculated. 13 ,θ 131 and the phase difference θ of the non-contact electro-optic crystal 14 14 (Step S21). 131 is the phase difference θ of the contact-type electro-optic crystal 13 13 and the phase difference θ of the non-contact electro-optic crystal 14 14 Measured in the same manner as above.

[0073] Next, the voltage measurement circuit 321 measures the phase difference θ 14 The phase change Δθ from the previous measurement value 14 Next, the voltage measurement circuit 321 calculates the phase change amount Δθ of the non-contact electro-optic crystal 14. 14 The threshold θ is set T It is confirmed whether the threshold value θ used in this step S13 is equal to or less than the threshold value θ (step S23). T is determined based on the voltage change ΔV of high voltage conductor 11 at which the influence of the electrostrictive effect of both contact electro-optic crystal 13 and contact electro-optic crystal 131 becomes no longer negligible.

[0074] The voltage measurement circuit 321 measures the phase change amount Δθ of the non-contact electro-optic crystal 14. 14 is the threshold θ T In the following case (step S23: Yes), the phase difference θ 13 and θ 131 That is, the voltage measurement circuit 321 calculates the voltage V of the high-voltage conductor 11 based on the phase difference θ 13 and the phase difference θ of the contact-type electro-optic crystal 131 131 The voltage V of the high voltage conductor 11 is calculated using the relationship:

[0075] The voltage measurement circuit 321 measures the phase change amount Δθ of the non-contact electro-optic crystal 14. 14 is the threshold θ T If it is not equal to or less than the above (step S23: No), the phase difference θ 14 Based on this, the voltage V of the high-voltage conductor 11 is calculated (step S15).

[0076] Next, the voltage measurement circuit 321 measures the phase change amount Δθ of the non-contact electro-optic crystal 14. 14 is the threshold θ T (Step S26). Time T is the time when the influence of the electrostrictive effect on contact electro-optic crystals 13 and 131 can be ignored. That is, this time T is the time when the influence of the electrostrictive effect on contact electro-optic crystals 13 and 131 can be ignored after a steep high voltage is applied to high voltage conductor 11, and the phase difference θ of contact electro-optic crystal 13 can be ignored. 13 and the phase difference θ of the contact-type electro-optic crystal 131 131 This is the time it takes for the correct voltage to be measured using the relationship between the voltage and the voltage applied, and is generally within 10 ms.

[0077] The voltage measurement circuit 321 measures the phase change Δθ 14 is the threshold θ T If the predetermined time T has not elapsed since the phase difference θ 14(Step S17). Next, the voltage measurement circuit 321 returns to step S15 and measures the phase difference θ 14 The voltage V of the high-voltage conductor 11 is calculated based on the above (step S15). 14 is the threshold θ T Steps S15, S26 and S17 are repeated until a predetermined time T has elapsed after the phase change amount Δθ 14 is the threshold θ T If the predetermined time T has elapsed since the time T was exceeded (step S26: Yes), the process returns to step S21, and step S21 and the subsequent steps (processing of each step) are repeated.

[0078] As described above, the voltage measuring device 1a according to the second embodiment includes contact electro-optic crystal 13, which is an electro-optic crystal in electrical contact with both high-voltage conductor 11, which is a conductor at the same potential as the voltage to be measured, and ground conductor 12, which is a conductor connected to a reference potential point; contact electro-optic crystal 131, which is an electro-optic crystal in electrical contact with both high-voltage conductor 11 and ground conductor 12 and has a half-wavelength voltage different from that of contact electro-optic crystal 13; and non-contact electro-optic crystal 14, which is an electro-optic crystal in electrical contact with either high-voltage conductor 11 or ground conductor 12. The voltage measuring device 1a according to the second embodiment includes contact electro-optic crystal 13, which is an electro-optic crystal in electrical contact with both high-voltage conductor 11 and ground conductor 12 and has a half-wavelength voltage different from that of contact electro-optic crystal 13. The phase difference θ of non-contact electro-optic crystal 14 is measured during a predetermined time period from when a steep voltage is applied to high-voltage conductor 11, that is, until the influence of the electrostrictive effects of contact electro-optic crystals 13 and 131 becomes negligible. 14 After a predetermined time has elapsed, the voltage measuring device 1a calculates the voltage V of the high-voltage conductor 11 based on the phase difference θ 13 and the phase difference θ of the contact-type electro-optic crystal 131 131 The voltage measuring device 1a can obtain the same effects as the voltage measuring device 1 according to the first embodiment, and further, before the voltage measuring circuit 321 measures the voltage V applied to the high-voltage conductor 11, it is necessary to apply a DC current to the high-voltage conductor 11 and calculate the voltage V of the high-voltage conductor 11 based on the above. 13 Even if a voltage V outside the range of π[V] is applied for a long period of time, the correct voltage can be measured.

[0079] Next, the hardware configuration of the voltage measurement circuit 32 of the voltage measurement device 1 according to the first embodiment and the voltage measurement circuit 321 of the voltage measurement device 1a according to the second embodiment will be described. The voltage measurement circuits 32 and 321 are realized, for example, by hardware having the configuration shown in FIG. 22, namely, a processor 91, a memory 92, and an interface 93. FIG. 22 is a diagram showing an example of hardware that realizes the voltage measurement circuits 32 and 321. The processor 91 is a CPU (Central Processing Unit, also referred to as a central processing unit, processing device, arithmetic unit, microprocessor, microcomputer, or DSP (Digital Signal Processor)), a system LSI (Large Scale Integration), or the like. The memory 92 is a RAM (Random Access Memory), a ROM (Read Only Memory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM (registered trademark), or the like. The interface 93 is a circuit for the voltage measurement circuits 32, 321 to exchange data with peripheral circuits, such as the light emitting and receiving units 20, 201 and the modulator driving circuit 31. The interface 93 is also used when outputting the voltage measurement results to an external device.

[0080] The voltage measurement circuits 32 and 321 may be implemented as a processing circuit such as a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof.

[0081] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0082] Various aspects of the present disclosure are summarized below as appendices.

[0083] (Appendix 1) a sensor unit including a plurality of electro-optic crystals, each having a first end face facing a high-voltage conductor having the same potential as the measurement target and a second end face facing a ground conductor on the opposite side to the first end face, and causing a phase difference in two polarized light components of light propagating between the first end face and the second end face, the polarized light components having mutually orthogonal vibration directions, depending on the strength of the electric field acting between the first end face and the second end face; a light projecting and receiving unit including, for each of the plurality of electro-optic crystals, a plurality of photodetectors that detect components of light that are included in the light emitted from the electro-optic crystal and whose polarization state has changed due to propagation between the first end face and the second end face; a signal processing unit that determines the voltage applied to the high-voltage conductor based on signals detected by each of a plurality of photodetectors corresponding to the plurality of electro-optic crystals; Equipped with The sensor unit a contact electro-optic crystal, the first end face of which is in electrical contact with the high-voltage conductor and the second end face of which is in electrical contact with the ground conductor; a non-contact electro-optic crystal in which the first end face is in electrical contact with the high-voltage conductor and the second end face is in electrical non-contact with the ground conductor, or the second end face is in electrical contact with the ground conductor and the first end face is in electrical non-contact with the high-voltage conductor; A voltage measuring device comprising: (Appendix 2) the distance between the first end face and the second end face of the non-contact electro-optic crystal is shorter than the distance between the first end face and the second end face of the contact electro-optic crystal; 2. A voltage measuring device according to claim 1. (Appendix 3) the non-contact electro-optic crystal has a first end face and a second end face each having a different shape; 3. The voltage measuring device according to claim 1 or 2. (Appendix 4) The voltage measuring device according to any one of appendixes 1 to 3, characterized in that when a steep voltage is applied to the high-voltage conductor, the signal processing unit determines the voltage applied to the high-voltage conductor based on the signal detected by the photodetector corresponding to the non-contact electro-optic crystal until the influence of the electrostrictive effect of the contact electro-optic crystal subsides. (Appendix 5) the signal processing unit determines the voltage applied to the high-voltage conductor using information on the voltage applied to the high-voltage conductor determined based on a signal detected by a photodetector corresponding to the contact electro-optic crystal and information on the time change of the voltage applied to the high-voltage conductor determined based on a signal detected by a photodetector corresponding to the non-contact electro-optic crystal; 5. A voltage measuring device according to any one of claims 1 to 4. (Appendix 6) The sensor unit a plurality of the contact-type electro-optic crystals; the phase difference occurring in the light propagating through each of the plurality of contact electro-optic crystals when the same voltage is applied to the high-voltage conductor is different for each of the contact electro-optic crystals; the signal processing unit determines the voltage applied to the high-voltage conductor based on a relationship between signals detected by the plurality of photodetectors corresponding to the plurality of contact electro-optic crystals; 6. A voltage measuring device according to any one of claims 1 to 5. [Explanation of symbols]

[0084] 1,1a voltage measuring device, 10,101 sensor unit, 11 high voltage conductor, 12 ground conductor, 13,131 contact electro-optic crystal, 13a,13b,13c,14a,14b,14c thin film, 14 non-contact electro-optic crystal, 15 Faraday rotator, 16,27 collimator lens, 17 electric field relaxation electrode, 20,201 light emitting / receiving unit, 21 light source, 22a,22b,22c,22d photodetector, 23 polarization modulator, 24 polarizer, 25a,25b,25c,25d analyzer, 26a,26b,26c,26d beam splitter, 30,301 signal processing unit, 31 modulator driving circuit, 32,321 voltage measuring circuit, 40 optical fiber.

Claims

1. a sensor unit including a plurality of electro-optic crystals, each of which has a first end face facing a high-voltage conductor having the same potential as the measurement target and a second end face facing a ground conductor on the opposite side to the first end face, and which generates a phase difference corresponding to the strength of the electric field acting between the first end face and the second end face in two polarized light components whose vibration directions are orthogonal to each other of light that is incident on the second end face, reflected by the first end face, and propagates along a path that returns to the second end face; a light projecting and receiving unit including a plurality of photodetectors that project light onto the second end face of each of the plurality of electro-optic crystals and detect components of light that are included in the light that is output from the second end face of the electro-optic crystal and whose polarization state has changed due to propagation through the path; a signal processing unit that determines the voltage applied to the high-voltage conductor based on signals detected by each of a plurality of photodetectors corresponding to the plurality of electro-optic crystals; Equipped with The sensor unit a contact electro-optic crystal, the first end face of which is in electrical contact with the high-voltage conductor and the second end face of which is in electrical contact with the ground conductor; a non-contact electro-optic crystal in which the first end face is in electrical contact with the high-voltage conductor and the second end face is in electrical non-contact with the ground conductor, or the second end face is in electrical contact with the ground conductor and the first end face is in electrical non-contact with the high-voltage conductor; Equipped with When a steep voltage is applied to the high-voltage conductor, the signal processing unit determines the voltage applied to the high-voltage conductor based on the signal detected by the photodetector corresponding to the non-contact electro-optic crystal until the influence of the electrostrictive effect of the contact electro-optic crystal subsides. A voltage measuring device characterized by:

2. the distance between the first end face and the second end face of the non-contact electro-optic crystal is shorter than the distance between the first end face and the second end face of the contact electro-optic crystal; 2. The voltage measuring device according to claim 1.

3. the non-contact electro-optic crystal has a first end face and a second end face that are different in size; 2. The voltage measuring device according to claim 1.

4. the signal processing unit determines the voltage applied to the high-voltage conductor using information on the voltage applied to the high-voltage conductor determined based on a signal detected by a photodetector corresponding to the contact electro-optic crystal and information on the time change of the voltage applied to the high-voltage conductor determined based on a signal detected by a photodetector corresponding to the non-contact electro-optic crystal; 2. The voltage measuring device according to claim 1.

5. The sensor unit a plurality of the contact-type electro-optic crystals; the phase difference occurring in the light propagating through each of the plurality of contact electro-optic crystals when the same voltage is applied to the high-voltage conductor is different for each of the contact electro-optic crystals; the signal processing unit determines the voltage applied to the high-voltage conductor based on a relationship between signals detected by the plurality of photodetectors corresponding to the plurality of contact electro-optic crystals; 5. The voltage measuring device according to claim 1, wherein the voltage measuring device is a voltage measuring device.

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