JPH10111320A - Photo-voltage/photo-current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the fluctuation of a direct current component caused by temperature generated in optical parts constituting a sensor part, an amplifying circuit in a light receiving circuit, or the like in a photo-voltage sensor provided with an electro-optic element and constituted in such a way as to measure the voltage of a power system from the transmitted light quantity, corresponding to applied voltage, of the electro-optical element. SOLUTION: Modulated light of frequency (6kHz, for instance) not less than double of system frequency (50Hz, for instance) of a power system to be measured is supplied to an electro-optic element 27 from a light emitting circuit 23, and its output light is separated into a 50Hz component and a 6kHz component by a basic wave filter 44 and a modulated wave filter 45 and divided by a divider 47. Only a voltage component to be measured after eliminating fluctuation of a direct current component caused by temperature generated in optical parts of a sensor part 22, a light receiving circuit 24, or the like can thereby be outputted, so that measuring accuracy can be improved while being usable in a wide temperature range.

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 of a power system 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. In particular, the present invention relates to a configuration for improving the 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 stray capacitance formed by a system charging conductor and a floating conductor arranged in parallel with the charging conductor, and a capacitor provided between the floating conductor and a ground potential, The voltage of the charging conductor is divided and applied. The electro-optical element has a transmitted light amount corresponding to the electric field by the applied voltage. Therefore, the amount of light corresponding to the voltage of the charging conductor is extracted,
By photoelectrically converting this light amount, a sensor output corresponding to the voltage of the charging conductor is created.

FIG. 4 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 made of optical components, a light emitting circuit 3, and a light receiving circuit 4. The sensor unit 2 includes a polarization detector 5, a λ / 4 plate 6, and an electro-optical element 7.
And the polarization detector 8 are arranged in this order.

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. The electro-optical element 7 is, for example, a BGO
It is realized by a Pockels element made of (Bi ₁₂ GeO ₂₀ ) crystal, and changes the amount of rotation corresponding to the applied voltage from the applied power supply 9 as the capacitor, whereby the output light from the electro-optical element 7 becomes Referring to FIG.
It becomes elliptically polarized light as shown by 2, α3.

In the light emitting circuit 3, the light emitting diode 11 is driven to emit light by a DC power supply 13. on the other hand,
In the light receiving circuit 4, the output from the photodiode 12 is amplified by an amplifier circuit 14, and then the output from a high-pass filter (HPF) 15 and a low-pass filter (LP)
F) 16 and are commonly input. The output from the high-pass filter 15 is divided by the output from the low-pass filter 16 in the divider 17 and output.

Therefore, the output of the divider 17 is a value obtained by dividing the AC component AC extracted by the high-pass filter 15 by the DC component DC extracted by the low-pass filter 16, and the change in the amount of light emitted by the light emitting diode 11 is obtained. Eliminating the effects of changes in the light receiving sensitivity of the photodiode 12 and changes in the transmission path loss of optical fibers and the like,
Accurate measurement of system voltage can be performed.

[0010]

In the optical voltage sensor 1 configured as described above, the output AC / D from the light receiving circuit 4 is obtained.
Although the influence of the error component appearing together with the AC component DC and the DC component DC such as the change in the light emission amount of the light emitting diode 11 described above is removed from C, one of the components, particularly the DC component DC, appears. There is a problem that the influence of errors due to temperature cannot be eliminated.

For example, the phase difference between two mutually perpendicular components of the light emitted from the λ / 4 plate 6 changes with temperature, and the DC component DC changes. Further, in the light receiving circuit 4, for example, the offset of the amplifier circuit 14 including a plurality of stages of differential amplifiers and the time constant of the capacitors constituting the filters 15 and 16 change with temperature, and the DC component DC varies. Sometimes.

These fluctuations of the DC component DC are not reflected on the AC component AC caused by the voltage applied by the application power supply 9, so that there is a problem that an accurate measurement of the system voltage cannot be performed.

A similar problem also occurs in a photocurrent sensor that detects a system current using a magneto-optical element such as a Faraday element instead of the electro-optical element 7.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical voltage / current sensor capable of performing high-precision measurement by eliminating the influence of fluctuation of a DC component due to temperature generated in an optical component or a light receiving circuit. is there.

[0015]

According to the optical voltage / current sensor of the present invention, light output from a light emitting element is incident on a sensor section having an electro-optical element or a magneto-optical element and detected by a light receiving element. From the transmitted light amount corresponding to the electric field or the magnetic field of the electro-optical element or the magneto-optical element, the voltage or the current of the power system is measured.
In the photocurrent sensor, a drive circuit that drives the light emitting element with a modulated wave having a frequency of twice or more the system frequency of the power system, and a fundamental wave filter that extracts a component of the system frequency from an output of the light receiving element. A modulation wave filter for extracting a frequency component of the modulation wave from an output of the light receiving element, a rectification circuit for rectifying and smoothing the output of the modulation wave filter, and an output of the fundamental wave filter for the rectification circuit. And a division circuit for dividing by the output.

According to the above configuration, even if the phase difference of the λ / 4 plate, the offset of the amplifier circuit in the light receiving circuit, the time constant of the filter, and the like change due to temperature, the light emitting element is driven by the modulated wave. Therefore, the influence of those fluctuations appears in both the output of the fundamental wave filter and the output of the modulated wave filter.

Therefore, by dividing the output of the fundamental wave filter by the rectified output of the modulation wave filter, the influence of the fluctuation due to the temperature can be eliminated, and highly accurate measurement can be performed. Can be used with

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.
The following is a description based on FIGS. 1 to 3 and 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. The sensor unit 22 includes a polarization detector 25 and a λ / 4 plate 2.
6, an electro-optical element 27, and a polarization detector 28 are arranged in this order.

The sensor section 22 is disposed in connection with a switchgear, and the remaining light emitting circuit 23 and the light receiving circuit 24 are disposed in a substation building or the like which is separated from the sensor section 22. 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 optical fiber and the collimator (not shown). The output light from the polarization detector 28 is received by the photodiode 41 of the light receiving circuit 24 via a collimator (not shown) and the optical fiber. Therefore, the polarization analyzer 25 acts as a polarizer, and the polarization analyzer 28 acts as an analyzer. The light emitting circuit 23 may face the polarization detector 28 and the light receiving circuit 24 may face the polarization detector 25. In this case, the polarization detector 28 acts as a polarizer and the polarization detector 2
5 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. Therefore, the light emitted from the λ / 4 plate 26 becomes circularly polarized light as shown by the reference numeral α1 in FIG. The electro-optical element 27 is realized by, for example, a Pockels element made of the BGO crystal, and changes its phase amount according to an applied voltage from an applied power supply 29 realized by a capacitor that divides a voltage of a system charging conductor. As a result, the output light from the electro-optical element 27 becomes elliptically polarized light as indicated by reference numerals α2 and α3 in FIG.

The light emitting circuit 23 includes the light emitting diode 31, a DC power supply 32, an oscillation circuit 33, and a modulation circuit 3.
4 is provided. The oscillating circuit 33 outputs a rectangular wave pulse of a system frequency which is a fluctuation frequency of a voltage applied to the electro-optical element 27 from the applied power supply 29, for example, at least twice or more, for example, 50 (Hz), for example, 6 (kHz). I do. The square wave pulse from the oscillation circuit 33 is
The signal is input to the modulation circuit 34. The modulation circuit 34 modulates the DC voltage from the DC power supply 32 with the rectangular wave pulse and supplies the modulated DC voltage to the light emitting diode 31. Thus, the light emitting diode 31 is driven by the modulated wave.

On the other hand, the light receiving circuit 24 includes the photodiode 41, an amplifying circuit 42, and a signal processing circuit 43. The amplification circuit 42 is realized by, for example, a multi-stage differential amplifier.

The signal processing circuit 43 includes a fundamental wave filter 44, a modulation wave filter 45, a rectifier circuit 46, and a divider 47. The output from the amplifying circuit 42 is commonly input to a fundamental wave filter 44 and a modulation wave filter 45. The fundamental wave filter 44
The modulation wave filter 45 is realized by a band-pass filter or the like that can extract a fundamental wave component, that is, a component of the system frequency of 50 (Hz). This is realized by a band-pass filter or the like that can extract a component of 6 (kHz), which is a frequency.

The output from the modulated wave filter 45 is provided to a rectifier circuit 46. The rectifier circuit 46 is realized by, for example, a diode bridge and a smoothing capacitor, and rectifies and smoothes the output from the modulated wave filter 45 and outputs the result. The output of the fundamental wave filter 44 is divided by the output from the rectifier circuit 46 in a divider 47.

FIG. 2 shows an example of a waveform associated with the operation of each section as described above. However, in order to facilitate understanding, the frequency of the modulated wave is 7.5 times the frequency of the fundamental wave. 2A shows a rectangular wave pulse from the oscillation circuit 33, FIG. 2B shows a driving waveform of the light emitting diode 31 by the modulation circuit 34, and FIG. The output light of the sensor unit 22 modulated by the influence of the DC component due to
2 (d) shows an output waveform of the fundamental wave filter 44, and FIG. 2 (e) shows an output waveform of the divider 47. Note that the output waveform of the rectifier circuit 46 is represented by reference numeral β in FIG.

As described above, λ / 4 accompanying temperature change
Variations in the DC component generated by the optical components due to changes in the phase difference of the plate 26, changes in the offset voltage of the amplifier circuit 42, and changes in the time constants of the capacitors in the filters 44 and 45 cause the light receiving circuit 24 to change due to temperature changes. The fluctuation of the DC component can also be removed by detecting the fluctuation by rectifying the modulated wave component and dividing the detected component by the fundamental wave component. Thus, the system voltage can be measured with high accuracy.

FIG. 3 is a block diagram showing the configuration of a test apparatus created by the present inventor to verify the characteristics of the optical voltage sensor 21 configured as shown in FIG. A sine wave signal of 50 (Hz) which is the system frequency oscillated by the oscillator 51 is input to a voltage input terminal of the sensor unit 22.
2, the signal is amplified after being amplified to an amplitude corresponding to the divided level. On the other hand, the light input / output terminal of the sensor unit 22 is connected to the light emitting circuit 23 and the light receiving circuit 24 via the optical fiber 53.
Each circuit in the light emitting circuit 23 and the light receiving circuit 24 includes a power supply 5
4 is energized. The output from the light receiving circuit 24 is input to a waveform analyzer 55 and also to a ratio error tester 56. The output from the oscillator 51 is directly input to the ratio error tester 56. The waveform analyzer 55 is a device that analyzes a frequency spectrum using, for example, FFT (Fast Fourier Transform), and its output is displayed and output by the printer 57.

In this experiment, the sensor section 22 was connected to the constant temperature bath 58
In order to avoid the influence of the induction from the power supply circuit 54 and the amplifier 52, a commercial frequency of 60 (Hz) is supplied to these power supplies, and the oscillation frequency of the oscillator 51 is set to 50 (Hz). I have. Further, the oscillation frequency of the oscillation circuit 33 in the light emitting circuit 23, that is, the modulation frequency is set to 27.
0 (Hz).

Table 1 shows the experimental results when the temperature in the thermostatic chamber 58 was lowered with reference to the room temperature of 22.3 (° C.).

[0032]

[Table 1]

In Table 1, the FFT value is the oscillation frequency of the oscillator 51, which is detected by the waveform analyzer 55, and is the component of 50 (Hz) which is the fundamental wave, and the oscillation frequency of the oscillation circuit 33, 270 which is the frequency of the modulated wave
(Hz) level. Also, the ratio error ε is
The magnitude of the error at each temperature with reference to the room temperature 22.3 (° C.) is shown. The conventional example is the case where the optical voltage sensor 1 shown in FIG. This is an actual measurement value of the ratio error tester 56. The present invention is a value obtained by calculation from the FFT value. Since the output of the divider 47 is a fundamental wave component / modulated wave component, 50 (Hz) component / 270 (Hz) It is the value of the component, and for example, at 2.1 (° C.), it can be determined as in the following equation.

[0034]

(Equation 1)

As is clear from Table 1, in the optical voltage sensor 21 according to the present invention, the influence of the fluctuation of the DC component due to the optical components and the light receiving circuit 24 on the temperature change is eliminated by using the modulated wave. , It can be understood that the ratio error ε is significantly improved. Thereby, highly accurate measurement can be performed, and the actual use environment, for example, −20 (° C.) to +80 (° C.)
Can be used over a wide temperature range.

It is needless to say that a photocurrent sensor for detecting a system current using a magneto-optical element such as a Faraday element can be similarly implemented. Further, the extraction of the fundamental wave component and the modulated wave component is not limited to the band pass filter, and another method such as FFT may be used. Further, the frequency of the modulated wave may be at least twice the system frequency according to the sampling theorem, and practically, the above-mentioned frequency of about 6 (kHz), which is less affected by system harmonics, is desirable.

[0037]

The optical voltage / current sensor according to the present invention comprises:
As described above, when measuring the voltage or current of the power system using the electro-optical element or the magneto-optical element, respectively, the light incident on the electro-optical element or the magneto-optical element from the light emitting element, the voltage to be measured or Modulated light having a frequency that is at least twice the system frequency of the current is used, and the output of the light receiving element divides the system frequency component by the modulation frequency component.

Therefore, the fluctuation of the DC component caused by the temperature in the optical component and the electric circuit can be removed, and the voltage or current to be measured can be measured with high accuracy, and it can be used in a wide temperature range. it can.

[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 waveform chart for explaining the operation of the optical voltage sensor shown in FIG.

FIG. 3 is a block diagram of a test apparatus of the present inventor for verifying an improvement effect of a temperature characteristic by the optical voltage sensor shown in FIG.

FIG. 4 is a block diagram showing a configuration of a typical conventional optical voltage sensor.

FIG. 5 is a diagram illustrating a change in polarization shape due to an electro-optic effect.

[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 27 electro-optical element 28 polarization detector 29 applied power supply 31 light emitting diode (light emitting element) 32 DC power supply (drive circuit) 33 oscillation circuit (Drive circuit) 34 Modulation circuit (Drive circuit) 41 Photodiode (light receiving element) 42 Amplification circuit 43 Signal processing circuit 44 Basic wave filter 45 Modulation wave filter 46 Rectifier circuit 47 Divider 51 Oscillator 52 Amplifier 53 Optical fiber 55 Waveform analyzer 56 Ratio error tester 58 Thermostat

Claims (1)

[Claims] 1. A light output from a light-emitting element is incident on a sensor unit having an electro-optical element or a magneto-optical element, and transmitted according to an electric field or a magnetic field of the electro-optical element or the magneto-optical element detected by a light receiving element. In a light voltage / current sensor configured to measure a voltage or a current of a power system from a light amount, a driving circuit that drives the light emitting element with a modulated wave having a frequency equal to or more than twice a system frequency of the power system, A fundamental wave filter that extracts the system frequency component from the output of the light receiving element; a modulation wave filter that extracts the frequency component of the modulation wave from the output of the light receiving element; and rectifies the output of the modulation wave filter. A rectifying circuit for smoothing; and a dividing circuit for dividing an output of the fundamental wave filter by an output of the rectifying circuit. .