JP2015011019A - DC voltage measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a direct-current voltage measurement device in which electric insulation is easily ensured.SOLUTION: A direct-current voltage measurement device according to an embodiment includes: an electro-optic crystal having first and second surfaces which are arranged on sides opposite to each other; first and second conductive layers being in close contact with the first and second surfaces, respectively, and transmitting infrared light; application means for applying a direct-current voltage across the first and second conductive layers; a light source for causing infrared light to be incident on the first conductive layer; and a light receiving part for receiving the infrared light incident on the first conductive layer, passing through the electro-optic crystal and emitted from the second conductive layer.

Description

  Embodiments described herein relate generally to a DC voltage measuring device that measures the voltage of power equipment and a power system of a substation or power plant.

  In order to measure a high voltage with high accuracy with little influence on insulation, a voltage sensor using light has been developed. Here, since the voltage includes AC and DC, the voltage sensor is required for AC measurement and DC measurement. Among these, the voltage sensor for AC measurement has already been put into practical use and is used for voltage measurement at power plants and substations (for example, see Non-Patent Document 1).

  On the other hand, voltage sensors for DC measurement have not been put into practical use, and only a few papers have been published. Among them, an optical voltage sensor using a chopper circuit has been implemented up to a field test (Non-Patent Document 2). That is, using a chopper circuit, the DC voltage is turned ON / OFF at 2 kHz and converted to AC, and then measured.

  However, in this optical voltage measuring device, the advantages of the optical voltage sensor that can easily ensure electrical insulation may be impaired as follows. That is, in order to chop the voltage to be measured, electronic components such as an O / E converter and a chopper circuit are required for the voltage detection unit. For this reason, it is difficult to ensure electrical insulation between a voltage detector that is likely to be exposed to a high-voltage surge or the like and an electronic component such as a protection relay or a measuring instrument that uses the measured signal.

1994 Joint Protection Committee on High Voltage Protection and High Voltage, SP-94-91, HV-94-162, Nakata, Hirata, Yoneda, Noda "Development of instrument transformer for 1000kVGIS" Watanabe et al. “Development of DC Photovoltage Transformer” The Institute of Electrical Engineers of Japan (1991)

  An object of this invention is to provide the direct-current voltage measuring apparatus which is easy to ensure electrical insulation.

  The direct-current voltage measuring apparatus according to the embodiment is in close contact with the electro-optic crystal having first and second surfaces arranged on opposite sides and to the first and second surfaces and transmits infrared light. First and second conductive layers; application means for applying a DC voltage between the first and second electrode layers; a light source for making infrared light incident on the first conductive layer; and the first conductive layer A light receiving portion that receives infrared light that is incident on the layer, passes through the electro-optic crystal, and is emitted from the second conductive layer.

It is a figure showing the DC voltage measuring device which concerns on embodiment. It is a figure showing an electro-optical element. It is a figure showing the equivalent circuit of an electro-optical element. It is a figure showing the relationship between the electric field direction of an electro-optic element, and a light transmissive direction.

  Hereinafter, embodiments will be described in detail with reference to the drawings. As shown in FIG. 1, the DC voltage measuring device 20 according to the embodiment includes an electro-optic element 10, a voltage divider 13, a light source 21, optical fibers 23a to 23c, a light-sending collimator unit 24, a polarizer 25, and a quarter wavelength. A plate 26, an analyzer 27, light receiving collimator units 28a and 28b, detectors 29a and 29b, and an electronic circuit 30 are provided.

(Details of electro-optical element 10)
First, the details of the electro-optical element 10 will be described. The electro-optic element 10 includes an electro-optic crystal 11 and conductive layers 12a and 12b.

The electro-optic crystal 11 is a crystal whose optical characteristics change (appears an electro-optic effect) when a voltage is applied. As an electro-optic effect, an effect (Pockels effect or the like) in which the refractive index is changed by applying voltage can be used. The Pockels effect is an effect in which the refractive index changes in proportion to the first power of the electric field strength. As the electro-optic crystal 11 having the Pockels effect, for example, BGO (Bi ₁₂ GeO ₂₀ ) or LN (LiNbO ₃ : lithium niobate) can be used.

  The conductive layers (electrode layers) 12a and 12b are conductive films formed in close contact with opposite surfaces (both ends) of the electro-optic crystal 11, and function as electrodes for applying a voltage to the electro-optic crystal 11. To do. Conductive layers 12a and 12b in close contact with the electro-optic crystal 11 can be formed by vapor deposition or sputtering. As a constituent material of the conductive layers 12a and 12b, a material that transmits infrared light from the light source 21, such as germanium (Ge) or silicon (Si), is used.

  Thus, the conductive layers 12a and 12b that transmit the measurement light (infrared light) are formed so as to be in close contact with both end faces of the electro-optic crystal 11, and the measurement light transmits both the conductive layers 12a and 12b. . In this way, a DC voltage can be applied to the conductive layers 12a and 12b and the voltage can be measured. The reason for this will be explained below.

  FIG. 2 is a diagram illustrating a polarization phenomenon in the electro-optic crystal 11. Here, the conductive layers 12 a and 12 b are not in close contact with the electro-optic crystal 11. FIG. 3 is an equivalent circuit of the electro-optic crystal 11 when the conductive layers 12a and 12b that are in close contact with each other are not used. FIG. 4 is a diagram illustrating the characteristics of the electro-optic crystal 11 in the case where the direction in which the electric field is applied and the direction in which light is transmitted match and are different.

  Conventionally, one of the reasons why optical measurement cannot be performed using the Pockels effect is the phenomenon of loss of polarization. That is, the polarization P is generated in the electro-optic crystal 11 by the DC electric field (see FIG. 2). However, since the electro-optic crystal 11 has some conductivity (resistance Rp), current flows and polarization disappears.

  In general, since the resistance of air is sufficiently large and negligible with respect to the resistance Rp of the electro-optic crystal 11, the electro-optic element 10 is a voltage dividing circuit of capacitances C1, C2 and CR (capacitance Cp, resistance Rp). (See FIG. 3). Capacitances C1 and C2 are capacitances between the electro-optic crystal 11 and the conductive layers 12a and 12b (air), respectively. Further, the capacitance Cp and the resistance Rp are the capacitance and resistance of the electro-optic crystal 11 itself, respectively.

  Considering the response when a step-like voltage change is applied to this circuit, the voltage V applied to the electrodes (conductive layers 12a, 12b) for applying an electric field is the capacitances C1, C2 in the air. The voltage is divided by the capacitance Cp of the electro-optic crystal 11. Further, the voltage across Cp is attenuated by the time constant of Cp * Rp by the resistance Rp of the electro-optic crystal 11 itself.

  From this, the following can be understood. First, in the case of direct current measurement, it is not preferable to apply a voltage to the electro-optic crystal 11 through a space because the voltage applied to the electro-optic crystal 11 is lowered. That is, it is necessary to apply a voltage to be measured directly to the surface of the electro-optic crystal 11. For this reason, electrodes (conductive layers 12a and 12b) are attached to both end faces of the electro-optic crystal 11, and are used by being electrically connected to the voltage to be measured. In this case, when the adhesion between the electro-optic crystal 11 and the electrodes (conductive layers 12a and 12b) is insufficient, it is difficult to accurately measure the voltage to be measured. That is, in AC measurement, it is connected by capacitance, and the influence on the measurement is relatively small. However, in DC measurement, even if it is a slight gap of about 1 nm, the resistance of the gap portion is The value becomes so large that the resistance of the electro-optic crystal 11 cannot be ignored. For this reason, the electrode is brought into close contact with the electro-optic crystal 11 by vapor deposition or sputtering.

In addition, if the resistance of the electro-optic crystal 11 is non-uniform, there is a possibility of measurement error (see FIG. 4). 4A and 4B show cases where the optical axis L and the electric field direction are orthogonal (lateral electric field type) and parallel (vertical electric field type), respectively. At this time, there is a possibility that the electric field concentrates in the vicinity of the electrodes (conductive layers 12a and 12b) due to non-uniform resistance. Here, the electric fields E1 and F5 near the conductive layers 12a and 12b are larger than the electric fields E2 to E5 away from the conductive layers 12a and 12b. For this reason, when the lateral electric field type orthogonal to the optical axis L is adopted, when light is transmitted through the center of the electro-optic crystal 11 (when the measurement light is affected by the electric field E3), When light is transmitted to the end (from the electrode) (when the measurement light is affected by the electric fields E1 and E5), the sensitivity is different (see FIG. 4B), and an error occurs.
In order to prevent such a phenomenon from occurring, even if the optical axis L is fixed to the electro-optic crystal 11, for example, if charges are trapped due to crystal defects or the like, they are trapped. Before and after, the electric field applied to the light transmission part is different, resulting in a measurement error.

  In order to prevent such an error due to the position of the measurement light, as shown in FIG. 4A, a vertical electric field that matches the optical axis and the applied electric field direction may be used. Even if the electric field in the electro-optic crystal 11 is nonuniform, the measurement light receives an integrated value of the electric field between the two electrodes, that is, a phase difference equal to the voltage applied to the electrodes, and the DC voltage is accurately determined. It can be measured.

  Also, the time constant of the disappearance of polarization varies depending on the measurement wavelength. Regarding this cause, it is appropriate to consider that the resistance Rp of the crystal shown in the equivalent circuit of FIG. 3 has changed. That is, it is suspected that the value of the resistance Rp of the electro-optic crystal 11 is changed by the measurement light. Such a phenomenon is known as a photoconductive effect, and the resistance value of the electro-optic crystal 11 may be reduced by light irradiation.

  In order to avoid this phenomenon, light having a wavelength that is long enough not to cause a photoconductive effect may be used as measurement light, and it is effective to use infrared light having a wavelength of 800 nm or more. Specifically, when the wavelength of the light used for measurement is 685 nm and 1310 nm, the time for which the polarization P disappears varies greatly from several seconds to several hundred seconds and several hours or more.

  In addition, since the resistance changes depending on the ambient light, it is required to shield the surroundings of the electro-optic crystal 11. However, the portion through which the measurement light passes needs to transmit light, and the measurement light passes therethrough. However, if the electrodes (conductive layers 12a and 12b) are made of a material that does not transmit visible light having a wavelength of 800 nm or less, the electro-optic crystal 11 can be effectively shielded from light. Specifically, the transmittance of visible light (visible light having a wavelength of 800 nm or less) in each of the conductive layers 12a and 12b is preferably 10% or less.

  At this time, the characteristics required for the electrode material are required to transmit infrared light for measurement, shield visible light, and have sufficient conductivity as an electrode. For example, germanium (Ge ), Silicon (Si), or the like can be used. The thickness of the conductive layers 12a and 12b is, for example, 0.1 to 2 μm (for example, 1 μm).

(Configuration other than electro-optical element 10)
Hereinafter, configurations other than the electro-optical element 10 will be described.

  The voltage divider 13 divides (reduces) the DC voltage and applies it to the electro-optical element 10 (conductive layers 12a and 12b). The voltage divider 13 has resistors R1 and R2 connected in series. The DC voltage V0 applied to the resistors R1 and R2 is divided by the resistor R1 and converted to the electric DC voltage V1.

  The voltage divider 13 functions as an application unit that applies a DC voltage between the conductive layers 12a and 12b. The voltage divider 13 and the conductive layers 12a and 12b can be connected by solder or the like. If the voltage to be measured is low to some extent, the voltage to be measured may be applied directly between the conductive layers 12a and 12b without using the voltage divider 13.

The light source 21 is, for example, a light emitting diode or a semiconductor laser that emits infrared light having a wavelength of 800 nm or more. The light source 21 causes infrared light to enter the electro-optical element 10 (conductive layer 12a).
The light source driving device 22 drives the light source 21 to emit infrared light.

The optical fibers 23 a to 23 c guide infrared light from the light source 21.
The light transmission collimator unit 24 converts divergent light emitted from the optical fiber 23a into parallel light using a lens or the like.

The polarizer 25 is an optical element that is disposed between the light source 21 and the conductive layer 12a and converts light that has passed through the light transmission collimator unit 24 into linearly polarized light.
The quarter-wave plate 26 is an optical element that is disposed between the polarizer 25 and the conductive layer 12a and converts linearly polarized light from the polarizer 25 into circularly polarized light.

  The analyzer 27 is disposed between the conductive layer 12b and the detectors 29a and 29b (light receiving portions), and infrared light having passed through the electro-optic element 10 is in the first and second polarization states orthogonal to each other. Separated into light (light of the first and second components).

  The light receiving collimator units 28a and 28b convert the first and second polarized light separated by the analyzer 27 into convergent light using a lens or the like, and enter the optical fibers 23b and 23c.

  Detectors (light receiving elements) 29a and 29b measure the intensities of the first and second components emitted from the optical fibers 23b and 23c. The detectors 29a and 29b function as a light receiving unit that receives infrared light that is incident on the conductive layer 12a, passes through the electro-optic crystal 11, and is emitted from the conductive layer 12b.

  The electronic circuit 30 calculates a voltage based on the measurement results of the detectors 29a and 29b. That is, the electronic circuit 30 functions as a calculation unit that calculates a voltage based on the ratio of the intensity of infrared light in the first and second polarization states measured by the detectors 29a and 29b.

(Operation of DC voltage measuring device 20)
The DC voltage measuring device 20 operates as follows.
Radiant light from the light source 21 driven by the light source driving device 22 enters the light transmission collimator unit 24 through the optical fiber 23a. The light transmission collimator unit 24 converts this incident light into a parallel light beam and supplies it to the polarizer 25. The polarizer 25 converts the incident parallel light into linearly polarized light, and the quarter wavelength plate 26 converts this linearly polarized light into circularly polarized light.

  The electro-optic element 10 converts the circularly polarized light incident through the quarter-wave plate 14 into elliptically polarized light according to the electric field strength applied to the electro-optic element 10. The light emitted from the electro-optic element 10 is transmitted through the analyzer 27 and light having only one polarization component is emitted. The amount of this light varies depending on the ellipticity that has been elliptically polarized by the electro-optic element 10 (a light amount corresponding to the voltage to be measured is output). The light is guided to the optical fibers 23b and 23c by the light receiving collimator units 28a and 28b and sent to the detectors 29a and 29b. After the optical signals are converted into electric signals by the detectors 29a and 29b, the voltage to be measured is calculated by the electronic circuit 30.

  The DC voltage measuring device 20 can measure not only AC but also DC voltage. For this reason, not only DC voltage measurement, but also AC line measurement, for example, transient waveforms including DC components during short-circuit accidents, etc., and superposition of DC voltage components due to positive and negative asymmetric loads such as diode loads The measured waveform can be measured accurately.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 10 Electro-optic element 11 Electro-optic crystal 12a, 12b Conductive layer 20 DC voltage measuring device 21 Light source 22 Light source driving device 23a-23c Optical fiber 24 Light transmission collimator part 25 Polarizer 26 1/4 wavelength plate 27 Analyzer 28a, 28b Light reception Collimator unit 29a, 29b Detector 30 Electronic circuit

Claims (8)

An electro-optic crystal having first and second surfaces disposed on opposite sides;
First and second conductive layers in close contact with each of the first and second surfaces and transmitting infrared light;
Applying means for applying a DC voltage between the first and second conductive layers;
A light source for making infrared light incident on the first conductive layer;
A light receiving portion that receives the infrared light that is incident on the first conductive layer, passes through the electro-optic crystal, and is emitted from the second conductive layer;
DC voltage measuring device comprising: The first and second conductive layers are formed by vapor deposition or sputtering on the electro-optic crystal;
The DC voltage measuring device according to claim 1. The DC voltage measuring device according to claim 1 or 2, wherein the wavelength of the infrared light is 800 nm or more. The direct-current voltage measuring device according to claim 3, wherein the visible light transmittance in each of the first and second conductive layers is 10% or less. The DC voltage measuring device according to claim 4, wherein the first and second conductive layers contain Ge or Si. A polarizer disposed between the light source and the first conductive layer;
An analyzer disposed between the second conductive layer and the light receiving unit;
The direct-current voltage measuring device according to claim 1, further comprising: A quarter wave plate disposed between the polarizer and the first conductive layer;
The analyzer separates infrared light emitted from the first conductive layer into infrared light in the first and second polarization states;
The light receiving unit includes first and second light receiving elements for receiving infrared light in the first and second polarization states,
The DC voltage measuring device according to claim 6. A calculation unit for calculating a voltage based on a ratio of the intensity of infrared light in the first and second polarization states measured by the first and second light receiving elements;
The DC voltage measuring device according to claim 7, further comprising:

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