JPH10111319A - Signal processing method and device for photo-voltage/ photo-current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the influence of a shift caused by the temperature change of phase difference in a λ/4 plate in a photo-voltage sensor constituted in such a way as to detect system voltage from the change of transmitted light quantity in relation to applied voltage, of an electro-optical element formed of a Pockels element or the like. SOLUTION: The added value of a low band component DCS, outputted after photoelectric conversion by a photodiode 32 and passed through an LPF 36, of reflected light from a polarization analyzer 28, and a low band component DCP, outputted after photoelectric conversion by a photodiode 33 and passed through an LPF 37, of transmitted light of the polarization analyzer 28, is obtained by an adder 38, and a high band component ACS of the above-mentioned reflected light output through an HPF 35 is divided by the obtained added value by a divider 39. Accordingly, even though the light quantity of either one of the transmitted light and reflected light is increased by the shift of phase difference following temperature change, the light quantity of the other is decreased, so that the added value remains constant, and the change of the high band component where an applied voltage change appears can be detected with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical voltage sensor for detecting a voltage using an electro-optical element such as a Pockels element and a photocurrent sensor for detecting a current using a magneto-optical element such as a Faraday element. The present invention relates to a signal processing method and apparatus for improving temperature characteristics.

[0002]

2. Description of the Related Art A voltage transformer is widely used for measuring a voltage of a power system. However, there is a problem in that the voltage transformer becomes larger as the system voltage to be measured becomes higher, resulting in an increase in cost and space. In particular, in a gas insulated switchgear using an inert gas called GIS, downsizing and space saving are strongly required, and it is difficult to mount such a voltage transformer.

[0003] For this reason, conventionally, an optical voltage sensor using an electro-optical element such as the Pockels element has been used. In the electro-optical element, a system charging conductor, a stray capacitance formed by a floating conductor arranged in parallel with the charging conductor, and a capacitor provided between the floating conductor and ground potential, The voltage of the charging conductor is divided and applied. The electro-optic element is
The transmitted light amount corresponding to the electric field by the applied voltage is extracted. Thus, the light amount corresponding to the voltage of the charging conductor is extracted, and the light amount is photoelectrically converted, whereby a sensor output corresponding to the voltage of the charging conductor is created.

FIG. 2 is a block diagram showing a configuration of a typical conventional optical voltage sensor 1. As shown in FIG. This optical voltage sensor 1
Is generally provided with a sensor unit 2 composed of optical components, a light emitting circuit 3, and a light receiving circuit 4 as a signal processing circuit. The sensor unit 2 includes a polarization detector 5 and a λ / 4 plate 6.
, The electro-optical element 7 and the polarization detector 8 are arranged in this order. The electro-optical element 7 is, for example, B
It is realized by a Pockels element made of GO (Bi ₁₂ GeO ₂₀ ) crystal, and changes the amount of transmitted light according to an applied voltage from an applied power supply 9 which is the capacitor.

The sensor section 2 is arranged in connection with the switchgear, and the remaining light emitting circuit 3 and light receiving circuit 4 are arranged in a substation building separated from the sensor section 2 and the like. , For example, may be 100 m or longer.

The light from the light emitting diode 11 of the light emitting circuit 3 is incident on the polarization detector 5 via the optical fiber and the collimator (not shown). Also, the output light from the polarization detector 8 is transmitted to the photodiode 1 of the light receiving circuit 4 via a collimator (not shown) and the optical fiber.
2 is received. Therefore, the polarization analyzer 5 acts as a polarizer, and outputs only light of a predetermined polarization direction from the incident light from the light emitting diode 11 to the λ / 4 plate 6, and the polarization analyzer 8 acts as an analyzer. Of the output light from the electro-optical element 7, only light having a predetermined polarization direction is output to the photodiode 12. It should be noted that the light emitting circuit 3 is
However, the light receiving circuit 4 may face the polarization detector 5. In this case, the polarization detector 8 acts as a polarizer, and the polarization detector 5
Acts as an analyzer.

The λ / 4 plate 6 converts the component of the incident light into a C-axis
The light is separated into an axis orthogonal to the C-axis, and these separated lights are mutually λ / 4, that is, π / 2
= 90 (°), so that the light emitted from the λ / 4 plate 6 becomes circularly polarized light as indicated by reference numeral α1 in FIG.

In the light emitting circuit 3, the light emitting diode 11 is driven to emit light by a power supply 13. On the other hand, in the light receiving circuit 4, the output from the photodiode 12 is commonly input to a high-pass filter (HPF) 14 and a low-pass filter (LPF) 15. The output from the high-pass filter 14 is divided by the divider 16 with the output from the low-pass filter 15 and output.

Therefore, the output of the divider 16 is a value obtained by dividing the AC component AC extracted by the high-pass filter 14 by the DC component DC extracted by the low-pass filter 15, and the output of the divider 16 changes the amount of light emitted from the light emitting diode 11. The system voltage can be accurately measured by removing the influence of the light amount loss due to the change in the light receiving sensitivity of the photodiode 12 and the change in the transmission line loss of the optical fiber or the like.

[0010]

In the optical voltage sensor 1 configured as described above, the input / output relationship of the λ / 4 plate 6 and the electro-optical element 7 can be expressed by the following equation (1).

I = (Io / 2) ｛1 ± Sin (Γv + δ)｝ (1) where Io is the amount of light after passing through the polarization detector 5;
Γv is a phase difference caused by the Pockels effect, and δ
Is the amount of shift of the phase difference in the λ / 4 plate 6 from 90 (°). I is the amount of light emitted from the polarization detector 8;
When the P component is transmitted through the polarization detector 8, sin
The term of (Γv + δ) becomes +, and when the S component is reflected light, the term of sin (Γv + δ) becomes-(in the example of FIG. 2, the reflected light, ie, the S component is Output). Here, the sin (Γv +
When δ) is small (≪1), Equation 1 can be approximated as Equation 2.

I = (Io / 2) {1 ± ({v + δ)} (2) The λ / 4 plate 6 has a temperature coefficient βa, and the operating temperature range of the optical voltage sensor 1 is Ta. Assuming that the phase difference after the shift according to the temperature is δa, δa = δo (1 + βa · Ta) (3) Here, δo is the phase difference at the reference temperature.

For example, the temperature coefficient βa of the λ / 4 plate 6
Is −1.014 × 10 ⁻⁴ (° / ° C.), the operating temperature range Ta is −20 to 80 (° C.), 100 (° C.), and δ
Substituting these numerical values assuming that o = π / 2 = 90 (°), δa = 90 ｛1 + (− 1.014 × 10 ⁻⁴ ) × 100｝ = 89 (°) (4) This means that a shift of δ = 1 (°) has occurred.

When the phase difference at the λ / 4 plate 6 deviates from the π / 2, the light emitted from the λ / 4 plate 6 becomes elliptically polarized light, as shown by reference numerals α2 and α3 in FIG. Become. As a result, it is not known whether the change in the amount of light of the output light from the electro-optical element 7 is due to the Pockels effect, that is, whether due to Δv or the shift amount δ, and the voltage applied to the electro-optical element 7 is accurately measured. Can not do it.

On the other hand, the light receiving / emitting circuits 4 and 3 also have temperature characteristics. For example, when the emission wavelength λ of the light emitting diode 11 has a temperature coefficient βb, and the temperature change width is Tb,
Λ / 4 plate 6 after being shifted by the change of the emission wavelength λ
Can be expressed as follows: δb = δo {λ / (λ + βbTb)} (5)

The emission wavelength λ is 850 (nm), the temperature coefficient βb is 0.25 (nm / ° C.), and the temperature change width Tb is 50
(° C.), δb = 90 ｛850 / (850 + 0.25 × 50)｝ = 88.7 (°) (6), which also causes a shift of δ = 1 (°) or more. become.

Therefore, δ = (δo−δa) + (δo
−δb) = 2 (°), sin (2 °) = 0.03
From equation (5), the above equation (2) becomes: I = (Io / 2) {1 ± ({v + 0.035)} (7), for example, the output AC / of the S component detected by the photodiode 12 from the divider 16 For DC, AC / DC = (Io / 2)） {v / {(Io / 2) (1−0.035)} = 1.036Γv (8), and an error of about 3.6% occurs. Will be. Therefore, there is a problem that highly accurate measurement cannot be performed over a wide temperature range.

A similar problem also occurs with a photocurrent sensor that detects a current using a magneto-optical element such as a Faraday element.

An object of the present invention is to eliminate the influence of the shift of the phase difference of a wave plate due to a temperature change and to provide a signal of an optical voltage / optical current sensor capable of performing highly accurate measurement over a wide temperature range. It is to provide a processing method and apparatus.

[0020]

According to the first aspect of the present invention, there is provided a signal processing method for an optical voltage / current sensor, comprising: a polarization detector, a wave plate, an electro-optical element or a magneto-optical element; A signal processing method for an optical voltage / optical current sensor, in which an optical signal is incident on an optical path provided with a device, and a voltage or a current is measured from a transmitted light amount of the electro-optical element or the magneto-optical element corresponding to an electric field or a magnetic field. , The transmitted light and the reflected light whose polarization planes output from the output polarizer are orthogonal to each other are photoelectrically converted by the first and second light receiving elements, respectively, and are output from the first and second light receiving elements. The low-frequency components of the output are respectively extracted and added to each other,
Alternatively, a high-frequency component of an output from any of the second light receiving elements is extracted, and the high-frequency component is divided by an added value of the low-frequency component.

According to a second aspect of the present invention, there is provided a signal processing device for an optical voltage / optical current sensor, comprising: an optical path including a polarization detector, a wave plate, an electro-optical element or a magneto-optical element, and a polarization detector. An optical signal is input to the signal processing device, and a voltage or a current is measured from the amount of light transmitted through the electro-optical element or the magneto-optical element corresponding to the electric or magnetic field. First and second light-receiving elements for receiving and photoelectrically converting transmitted light and reflected light whose polarization planes output from the polarization detector are orthogonal to each other, and outputs from the first and second light-receiving elements. First and second low-pass filters respectively extracting low-pass components of the first and second components, an adder for mutually adding outputs from the first and second low-pass filters, and the first or second light receiving element Any of A high-pass filter for extracting a high frequency component of the output, characterized in that it comprises a divider for dividing an output from said high-pass filter at the output from the adder.

According to the above arrangement, the first and second light receiving elements are opposed to the output side polarization detector, and the output from both the light receiving elements, that is, the transmission is made in parallel with the polarization direction of the polarization detector. The sum of the low-frequency component of the P component output as light and the low-frequency component of the S component output perpendicularly to the polarization direction and reflected as light, and the high-frequency component of the output from either the first or second light receiving element. Is divided. Thus, the added value of the low-frequency component remains constant even when the phase difference between the two output light components from the wavelength plate due to a temperature change.

Therefore, the influence of the wavelength plate on the temperature change can be removed, and highly accurate measurement can be performed over a wide temperature range. The addition value of the low-frequency component varies depending on, for example, a change in the amount of light emitted from the light-emitting element, a change in the light-receiving sensitivity of the light-receiving element, a transmission path loss, and the like. And can therefore be removed by division.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.
It is as follows if it demonstrates based on FIG. 1 and said FIG.

FIG. 1 is a block diagram showing a configuration of an optical voltage sensor 21 according to one embodiment of the present invention. This optical voltage sensor 21 is roughly composed of a sensor unit 22 composed of optical components.
, A light emitting circuit 23, and a light receiving circuit 24 as a signal processing circuit
It is comprised including. The sensor unit 22 includes a polarization detector 25, a λ / 4 plate 26, an electro-optical element 27, and a polarization detector 28 arranged in this order. The electro-optical element 27 is realized by a Pockels element made of, for example, the BGO crystal, and changes the amount of transmitted light according to an applied voltage from an applied power supply 29 realized by a capacitor that divides the voltage of a system charging conductor. .

The sensor section 22 is arranged in connection with a switchgear, etc., and the remaining light emitting circuit 23 and light receiving circuit 24 are arranged in a substation building separated from the sensor section 22, for example. Not connected by optical fiber.

Light from the light emitting diode 31 of the light emitting circuit 23 is incident on the polarization detector 25 via the unillustrated optical fiber and collimator. The output light from the polarization detector 28 is received by the photodiodes 32 and 33 of the light receiving circuit 24 via a collimator (not shown) and the optical fiber. Therefore, the polarizer 25 acts as a polarizer, and the light emitting diode 31
Out of the incident light from
Output to the plate 26, the polarization analyzer 28 acts as an analyzer,
The output light from the electro-optical element 27 is converted into the S component of reflected light perpendicular to the polarization direction of the polarization detector 25 and the P component of parallel transmitted light.
And the photodiodes 32,
33. It should be noted that the light emitting circuit 23 is
However, the light receiving circuit 24 may face the polarization detector 25,
In this case, the polarizer 28 acts as a polarizer, and the polarizer 25 acts as an analyzer.

The λ / 4 plate 26 separates the component of the incident light into a C-axis and an axis orthogonal to the C-axis. Thus, the light emitted from the λ / 4 plate 26 becomes circularly polarized light as indicated by α1 in FIG.

In the light emitting circuit 23, the light emitting diode 31 is driven to emit light by a power supply 34. On the other hand, in the light receiving circuit 24, the output from the photodiode 32 is commonly input to the high-pass filter 35 and the low-pass filter 36. Also, the photodiode 33
Are input to the low-pass filter 37.
Outputs from the low-pass filters 36 and 37 are added to an adder 38.
Are added to each other. In the divider 39, the output from the high-pass filter 35 is divided by the output from the adder 38 and output.

Therefore, the output of the divider 39 is the AC component ACS component of the S component extracted by the high-pass filter 35.
Is divided by the sum of the DC components DCS and DCP extracted by the low-pass filters 36 and 37. For example, as described above, when δ = 2 (°) in the same manner as in the equation 8, the equation 2 , ACS / (DCS + DCP) = (Io / 2) {v / {(Io / 2) (1-0.035) + (Io / 2) (1 + 0.035)} = {v / 2 ... (9)

Therefore, the λ / 4 plate 26 due to the temperature change
It can be understood that only the phase difference Δv by the electro-optical element 27 can be extracted without being affected by the shift of the phase difference.

The change in the amount of light emitted by the light emitting diode 31, the change in the light receiving sensitivity of the photodiodes 32 and 33, and the change in the transmission path loss of the optical fiber and the like as described above are caused by the AC component ACS as well as the DC components DCS and DCP. Are not affected by these. Furthermore, compared to the above-described optical voltage sensor 1, it is only necessary to add the photodiode 33, the low-pass filter 37, and the adder 38, so that highly accurate measurement can be performed with a simple configuration.

It is needless to say that a temperature characteristic can be similarly improved for a photocurrent sensor that detects a current using a magneto-optical element such as a Faraday element. Further, the AC component ACS and the DC component DCS,
The extraction of the DCP is not limited to the high-pass filter 35 and the low-pass filters 36 and 37, and other methods such as FFT (Fast Fourier Transform) may be used.

[0034]

According to the signal processing method for an optical voltage / photocurrent sensor according to the first aspect of the present invention and the signal processing device for an optical voltage / optical current sensor according to the second aspect of the present invention, as described above, An optical voltage / current sensor that includes an analyzer, a wave plate, an electro-optical element or a magneto-optical element, and a polarization analyzer, and measures a voltage or a current from the amount of light transmitted through the electro-optical element or the magneto-optical element, respectively. In processing the signal, the high-frequency component of the output light of the output side polarizer is divided by the low-frequency component of the output light to change the amount of light emitted from the light emitting element, change the light receiving sensitivity of the light receiving element, and transmit An effect due to a change in path loss or the like can be removed, and the low-frequency component is a sum of transmitted light and reflected light of the polarization detector.

Therefore, even with respect to the shift of the phase difference in the wavelength plate due to the temperature, it is possible to extract only the variation due to the applied voltage without changing the added value of the low frequency component. . As a result, it is possible to remove the influence of the temperature change of the wave plate and perform highly accurate measurement over a wide temperature range.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an optical voltage sensor according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a typical conventional optical voltage sensor.

FIG. 3 is a diagram for explaining a change in polarization shape due to a shift of a phase difference generated in a λ / 4 plate.

[Explanation of symbols]

 Reference Signs List 21 light voltage sensor 22 sensor unit 23 light emitting circuit 24 light receiving circuit 25 polarization detector 26 λ / 4 plate (wavelength plate) 27 electro-optical element 28 polarization detector 31 light emitting diode (light emitting element) 32 photodiode (first light receiving element) 33) Photodiode (second light receiving element) 34 Power supply 35 High pass filter (high pass filter) 36 Low pass filter (first low pass filter) 37 Low pass filter (second low pass filter) 38 Adder 39 Divider

Claims (2)

[Claims] An optical signal is incident on an optical path including a polarization detector, a wave plate, an electro-optical element or a magneto-optical element, and a polarization detector, and the electro-optical element or the magnetic element corresponding to an electric field or a magnetic field. In a signal processing method of an optical voltage / current sensor, wherein a voltage or a current is measured from an amount of light transmitted through an optical element, the transmitted light and the reflected light whose polarization planes output from the polarization analyzer on the output side are orthogonal to each other. The light is photoelectrically converted by first and second light receiving elements, respectively, and the low-frequency components of the outputs from the first and second light receiving elements are respectively extracted and added to each other, and the first or second light receiving is performed. A signal processing method for an optical voltage / photocurrent sensor, comprising: extracting a high-frequency component of an output from any of the elements; and dividing the high-frequency component by an added value of the low-frequency component. 2. An electro-optical element or a magnetic element corresponding to an electric field or a magnetic field, wherein an optical signal is incident on an optical path including a polarization detector, a wave plate, an electro-optical element or a magneto-optical element, and a polarization detector. In a signal processing device of an optical voltage / current sensor that measures a voltage or a current from the amount of light transmitted through an optical element, respectively, the transmitted light and the reflected light whose polarization planes output from the output polarizer are orthogonal to each other are provided. First and second light receiving elements that respectively receive light and perform photoelectric conversion, first and second low pass filters that respectively extract low frequency components of outputs from the first and second light receiving elements, An adder for mutually adding outputs from the first and second low-pass filters; a high-pass filter for extracting a high-frequency component of an output from one of the first and second light receiving elements; High pass filter The signal processing apparatus for an optical voltage · photocurrent sensor, characterized in that it comprises a divider for dividing the output of et at the output from the adder.