JPH04344469A - Light-applied direct current transformer - Google Patents

Abstract

PURPOSE:To enable direct currents to be measured over a wide area even if the quantity of light is fluctuated at light sources and at a light signal transfer portion by using a Faraday element to eliminate the influence of fluctuations in the quantity of light at the light sources and the light signal transfer portion. CONSTITUTION:Incident light from two light sources 1, 2 of different wavelengths lambda1, lambda2 is guided to a Faraday element 6. A first light wave 3 of the wavelength lambda1 is linearly polarized by a polarizer 5 disposed at the incident end of the element 6 and is allowed to circulate and pass through the element and then undergoes Faraday rotation proportional to a current value. A second light wave 4 of the wavelength lambda2 is not affected by the current to be measured since the light wave 4 is branched 16. At the light emission end of the element 6 a light signal of (lambda1+lambda2) is divided by an analyzer 7 into a P polarized light component and an S polarized light component which are perpendicular to each other, and the light components of (lambda1+lambda2) contained in both the P polarized light component and the S polarized light component are separated whereby four light signal components are obtained. These two P polarized light components and two S polarized light components obtained are transferred to a signal processing circuit 30 on the same light transfer line.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power transformer, and more particularly to an optical DC current transformer suitable for measuring a current having a DC component.

0002

2. Description of the Related Art In recent years, with the advancement of optoelectronics, it has become possible to measure electromagnetic quantities, ie, voltage, current, etc., using optical methods. Regarding the measurement principles and configuration systems of voltage and current using such optical methods, see, for example, Kazuo Kuma and Masahiro Nunoshita.
Co-authored “Optical Fiber Sensor” (Published by Information Research Committee, 1986)
(January 2013), etc. Most of this describes the measurement of alternating current signals, but also describes the measurement of direct current. Among them, a processing method is described as a dual-light output method in which the output signal of the sensor is divided into two orthogonal polarization components, that is, a P-polarization component and an S-polarization component, and the processing method is divided by the sum and difference of these components. Fluctuations in the amount of light in the transmission lines, signal processing circuits, etc. cause measurement errors, making it difficult to measure DC current with high precision if the method is used as is.

[0003] Therefore, as described in Japanese Patent Laid-Open No. 57-141562, a method has been proposed that uses a light source in which a high-frequency signal is superimposed on a DC signal to correct the light source fluctuation. Since this method does not take into account that the amount of light changes depending on the magnitude of the DC current to be measured, there is a problem in that it is difficult to sufficiently correct for fluctuations. Furthermore, in Japanese Patent Application Laid-Open No. 59-190668, light of two different wavelengths is used, the first light is polarized within the sensor, the second light is not polarized within the sensor, and the received intensity of both lights is A method has been proposed in which the variation is corrected from the ratio of

0004

[Problems to be Solved by the Invention] As mentioned above, in conventional optical direct current measurement, effective correction is not performed for variations in light intensity at various parts from the light source to the optical signal transmission line and the signal processing circuit. Therefore, there was a problem in that it was not possible to measure DC current with high accuracy. An object of the present invention is to measure DC current with high precision over a wide range even if the amount of light varies in the light source, optical signal transmission unit, etc.

[0005]

[Means for Solving the Problems] The above problems require a light source that generates a constant output light, a polarizer that linearly polarizes the light emitted from the light source, and a current conductor to be measured that has a magneto-optic effect. In an optical current transformer comprising a surrounding medium, an analyzer, and a signal processing circuit that converts an optical signal emitted from the light signal into an electrical signal and performs arithmetic and processing, the light source is a light wave with a wavelength λ1. a light source that emits a light wave with a wavelength λ2; a means for transmitting a light wave with a wavelength λ1 through the medium having the magneto-optical effect so as to surround the current conductor to be measured; and a light source that emits a light wave with a wavelength λ2 through the medium. means for branching at the entrance to the medium so that the medium does not pass through;
means for combining a light wave with a wavelength λ1 that has passed through the medium and a light wave with a wavelength λ2 that has not passed through the medium and then separating it into a P-polarized light component and an S-polarized light component;
A transmission line that transmits each polarized light component and the transmitted P
The polarized light component and the S-polarized light component have wavelengths λ1 and λ2, respectively.
This is achieved by comprising means for separating the optical output signals into two, and a signal processing circuit that performs sum-difference calculation processing on the separated optical output signals to obtain an electrical output signal having the same polarity as the current to be measured.

The above problem also requires an optical multiplexer that superimposes a light wave emitted from a light source that emits a light wave with wavelength λ1 and a light wave emitted from a light source that emits a light wave with wavelength λ2, and a an optical fiber that guides the light into a medium having a magneto-optic effect; and a dichroic that is disposed at the entrance of the medium and allows a light wave with a wavelength λ1 to pass into the medium and allows a light wave with a wavelength λ2 to enter the analyzer without passing through the medium. This is also achieved by the optical DC current transformer according to claim 1, which comprises:

[0007] The above-mentioned problem is further solved by means of making λ1 and λ2 the same wavelength and superimposing a high frequency on the light that does not pass through a medium having a magneto-optic effect, and a means for superimposing a high frequency on the light that does not pass through a medium having a magneto-optic effect, and a means for superimposing a high frequency on the light that does not pass through a medium that has a magneto-optic effect, and a means for superimposing a high frequency on the light that does not pass through a medium that has a magneto-optic effect, 2. The method according to claim 1, further comprising a photoelectric conversion means for photoelectrically converting the component, a separation means for separating the output of the photoelectric conversion means into a DC component and an AC component, and an arithmetic circuit for processing the output of the separation means. This can also be achieved by optically applied DC current transformers.

[0008]

[Operation] Incident light from two light sources with different wavelengths λ1 and λ2 is guided to a medium having a magneto-optic effect (hereinafter referred to as a Faraday element) (magnetic field sensor) through an optical transmission line using an optical fiber. The first light wave with wavelength λ1 is linearly polarized by a polarizer placed at the input end of the Faraday element, and then passes around the current conductor to be measured through the element, causing Faraday rotation according to the current value. receive. On the other hand, the second light wave having the wavelength λ2 is branched at the input end of the Faraday element so as not to pass through the Faraday element, and therefore is not affected by the current to be measured. At the light output end of the Faraday element, (λ
1+λ2) optical signal is divided into mutually orthogonal P-polarized light component and S-polarized light component, and the (λ1+λ2) light component included in each of the P-polarized light component and S-polarized light component is demultiplexed into four components in total. Optical signal components, that is, P-polarized light components Iλ1p and S-polarized light components Iλ1s of wavelength λ1, and P-polarized light components Iλ2p and S-polarized light components Iλ2p of wavelength λ2 are obtained. The two obtained P-polarized light components are transmitted to the signal processing circuit through the same optical transmission path for P-polarized light including an optical fiber, and the two S-polarized light components are also transmitted through the same optical transmission path for S-polarized light.

Here, Ip and Is are the P-polarized component and the S-polarized component of the light wave of wavelength λ1 obtained when no current flows through the current conductor to be measured, and the light wave of the first wavelength λ1 is generated in the Faraday element. Letting the Faraday rotation angle of Δφ, the above four optical signal components can be respectively expressed by the following equations.

0010

[Equation 1] P polarization component of light wave with wavelength λ1 Iλ1p
=Ip・(1−sinΔφ)

[0011]

[Equation 2] S polarization component of light wave with wavelength λ1 Iλ1s
=Is・(1+sinΔφ)

0012

[Formula 3] P polarization component of light wave with wavelength λ2 Iλ2p=Ip'

[0013]

[Formula 4] S polarization component of light wave with wavelength λ2 Iλ2s=Is'
here,

[0014]

[Equation 5] Kp=Ip/Ip'Ks=Is/Is' Since the P-polarized light component and the S-polarized light component of the light waves with wavelengths λ1 and λ2 respectively follow the same optical transmission path, the light including the light source Even if there is a change in the amount of light in the transmission path, Kp and Ks will change at the same rate. In other words, in the signal processing circuit

[0015]

[Equation 6] Once Kp and Ks are set so that K=Kp=Ks, it is possible to always keep K constant even if the light intensity fluctuates for some reason in the light source and the optical transmission path. Become. As a result, the output of the Faraday element is Jp for the P polarization component and Jp for the S polarization component.
s, each is expressed by the following formula.

[0016]

[Math 7]

[0017]

[Math. 8]

When these sums and differences are taken and divided, the output Vout becomes as follows.

[0019]

[Math. 9]

[0020] Here, if Δφ≪1, sinΔφ
≒Δφ, so if we perform the above calculation, we get
Even if there is a variation in light intensity at each part of the light source and optical transmission path, the Faraday rotation angle Δφ can be accurately determined, and the direct current can be measured with high precision over a wide range.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. The optical current transformer according to the present invention shown in FIG. 1 includes a light source 1 that generates two different wavelengths λ1 and λ2;
2, and an optical fiber 3 connected to the light sources 1 and 2, respectively.
, 4, and a prism 16' and a polarizer 5 on the optical fiber 3.
a Faraday element 6 having a magneto-optic effect connected via a Faraday element 6, an analyzer 7 connected to a light exit of the Faraday element 6, and a prism 16 connecting between the analyzer 7 and the optical fiber 4; Optical fibers 8 and 9 are connected to the light exit of the analyzer 7, and an optical demultiplexer 10 is connected to the optical fibers 8 and 9, respectively, and separates the incident light into two wavelengths λ1 and λ2 and outputs the two. , 11, and photodiodes 12, 1 connected to the output sides of the optical demultiplexers 10, 11 for photoelectric conversion.
3, 14, 15, and the photodiodes 12, 13, 1
4 and 15. The Faraday element 6 is formed to surround the current conductor 21 to be measured, and the light incident on the Faraday element is configured so that it travels around the current conductor 21 to be measured and then enters the analyzer 7. The photodiodes 12, 13, 14, 15 and the arithmetic processing circuit 20
A signal processing circuit 30 is formed. FIG. 2 shows details of the input/output portion of light waves of wavelengths λ1 and λ2 into and out of the Faraday element 6 shown in FIG. The light wave of wavelength λ2 is non-polarized light and is structured to be directly incident on the analyzer 7 without passing through the Faraday element. Prisms 16', 16'' are total reflection prisms for directing light.

Next, the flow of light waves in the device having the above configuration will be explained. Two light waves with different wavelengths λ1 and λ2 (hereinafter referred to as light wave λ1 and light wave λ2) are emitted from light sources 1 and 2, light wave λ1 is transmitted to optical fiber 3, and light wave λ2 is transmitted to optical fiber 4.
, respectively. Of these, the light wave λ1 is guided by the polarizer 5 and polarized into linearly polarized light, and then passes around the current conductor 21 to be measured while being totally reflected in the Faraday element 6. The light wave λ1 passes through the current conductor 21 to be measured, undergoes Faraday rotation proportional to the magnitude of the current to be measured, and enters the analyzer 7. On the other hand, although the light wave λ2 is guided to the entrance of the Faraday element by an optical fiber 4 different from the light wave λ1, it is branched by the prism 16 so as not to pass through the Faraday element 6, and directly enters the analyzer 7. In the analyzer 7, both the light wave λ1 and the light wave λ2 are divided into two orthogonal polarization components, a P polarization component and an S polarization component. Of the polarized light components separated in this way, the P polarized light component of the light wave λ1 and the P polarized light component of the light wave λ2 are transmitted through the fiber 8, and the S polarized light component of the light wave λ1 and the S polarized light component of the light wave λ2 are transmitted through the fiber 9. The signal is sent to demultiplexers 10 and 11. The optical demultiplexers 10 and 11 separate the P-polarized light component and the S-polarized light component into two optical signals with wavelengths λ1 and λ2, respectively, and transmit the resulting four signals to the signal processing circuit 30. The four optical signals transmitted to the signal processing circuit 30 are first converted into electrical signals by the photodiodes 12, 13, 14, and 15, and then transmitted to the arithmetic processing circuit 20.

FIG. 3 shows the configuration of an embodiment of the arithmetic processing circuit 20 of FIG. 1, in which photodiodes 12, 13,
Amplifiers 31, 32, 3 connected to 14, 15, respectively
3, 34, a divider 35 connected to the output sides of the amplifiers 31, 32, a divider 36 connected to the output sides of the amplifiers 33, 34, and a divider 36 connected to the output sides of the dividers 35, 36. An adder 37 connected, a subtracter 38 connected to the output sides of both the dividers 35 and 36, and a divider 39 connected to the output sides of the adder 37 and the subtracter 38.
It is composed of:

The P polarization component Iλ1p of the light wave λ1 is transmitted by the photodiode 12, the S polarization component Iλ1s is transmitted by the photodiode 14, and the P polarization component I of the light wave λ2 is transmitted by the photodiode 12.
The λ2p and S-polarized components Iλ2s are converted into electric signals by photodiodes 13 and 15, respectively, and amplified by amplifiers 31, 32, 33, and 34, respectively. Then, in the dividers 35 and 36, division Iλ1p/I for each P and S polarization component
λ2p, Iλ1s/Iλ2s are performed. Further, in the next stage adder circuit 37, Iλ1p/Iλ2p+Iλ1s/Iλ2
The addition s is performed by the subtraction circuit 38 as Iλ1p/Iλ2p−I
After the subtraction λ1s/Iλ2s is performed, the divider 39 obtains the output signal Vout shown in Equation 10 below.

[0025]

[Math. 10]

As described above, this output signal is proportional to the Faraday rotation angle and is not affected by variations in the amount of light.
Highly accurate DC current measurement becomes possible.

FIG. 4 shows a second embodiment of the present invention. The difference between this embodiment and the first embodiment is that the light waves of two different wavelengths λ1 and λ2 emitted from light sources 1 and 2 are guided to an optical multiplexer 18 and input into one optical fiber 19. and a point where a dichroic (hereinafter referred to as an optical filter 17) is arranged on the optical axis of the light waves λ1 and λ2 linearly polarized by the polarizer 5. Each light wave becomes linearly polarized light in the polarizer 5, and the light wave λ1 is guided into the Faraday element 6 by the subsequently provided optical filter 17, and after going around the current conductor 21 to be measured while being totally reflected, it is sent to the analyzer. However, the light wave λ2 is branched by the optical filter 17 so as not to pass through the Faraday element, and is incident on the analyzer 7. The operation in which the P-polarized light component and the S-polarized light component are transmitted after passing through the analyzer 7 and subjected to various signal processing is similar to that described in FIGS. 1 to 3 and has the same configuration. ing. This embodiment also provides the same effects as the first embodiment.

FIG. 5 shows a third embodiment of the present invention, and this embodiment differs from the first embodiment in the processing method of the signal after leaving the light source and analyzer 7. In this embodiment, the light source 1 is configured to emit a first light wave with a wavelength λ1, and the light source 2 is configured to emit a second light wave in which a high frequency is superimposed on the light wave of the wavelength λ1. Also,
The optical fiber 9 that transmits the S-polarized light component is a photoelectric converter 12A.
, the optical fiber 8 transmitting the P-polarized light component is connected to the photoelectric converter 1.
4A, respectively. Further, a low-pass filter LPF40A and a high-pass filter HPF40B are connected in parallel to the output side of the photoelectric converter 12A, and the output side of the low-pass filter LPF40A is connected to the divider 35, and the output side of the high-pass filter HPF40B is connected to the divider 35 through a smoothing circuit. and is connected to the divider 35. A low pass filter LPF40C is also installed on the output side of the photoelectric converter 14A.
and high-pass filter HPF40D are connected in parallel with each other, the output side of low-pass filter LPF40C is connected to divider 36, and the output side of high-pass filter HPF40D is connected to divider 36 via a smoothing circuit. The output sides of the dividers 35 and 36 are connected to a sum-difference circuit 39A.

Jo is the amount of the first light wave emitted from the first light source, J1+dsinωt is the amount of second light wave emitted from the second light source, and ηA, ηc are the optical attenuation rates of the optical fibers 3 and 4. , the optical attenuation rate of the Faraday element 6 is ηB, the optical attenuation rates of the optical fibers 8 and 9 are ηp, ηs, and the rotation angle of the Faraday element 6 is Δφ, and the operation of light in this embodiment will be described. As in the first embodiment, the first light wave emitted from the first light source is incident on the Faraday element via a polarizer, and the second light wave on which a high frequency has been superimposed is incident on the Faraday element. Instead, it enters the analyzer 7 directly. The first light wave that is incident on the analyzer via the Faraday element and the second light wave that is directly incident on the analyzer 7 are separated by the analyzer into a P-polarized light component and an S-polarized light component, and the P-polarized light component is The S-polarized light component is transmitted via fiber 9 to photoelectric converter 12A, and the S-polarized component is transmitted via optical fiber 8 to photoelectric converter 14A.

Now, the photoelectric converter 12A is connected via the optical fiber 8.
When the amount of light incident on the optical fiber 9 is Jp, and the amount of light incident on the photoelectric converter 14A via the optical fiber 9 is Js, Jp and Js are expressed by the following equations.

[0031]

[Formula 11] Jp=[Jo・ηA・ηB(1−Δφ)+ηc
・(J1+dsinwt)ηp Js=[Jo・
ηA・ηB(1+Δφ)+ηc・(J1+dsinwt
]ηs LPF40A extracts the DC component of Js and converts it to H
PF40B takes out the alternating current portion of Js. Similarly L
PF40C takes out the DC component of the above Jp and converts it to HPF4
0D takes out the AC component of the above Jp. Divider 35,3
6 is the ratio of input DC and AC components (DC component/AC component)
is calculated and output to the next stage arithmetic circuit 39A. The sum-difference circuit 39A calculates an output voltage Eout proportional to the magnitude of the current to be measured or the magnetic field to be measured by calculating the input signal using the following equation. (A': amplification factor of sum-difference circuit)

[0032]

[Math. 12]

That is, it is sufficient to set J1ηc/JoηA·ηB≪1, or even if these vary, the effect thereof is small. For example, if J1・ηc/Jo・ηA・ηB=0.1, for a 10% change in light intensity, the change in Eout is 1%, 1
This is a change of about 9% compared to a /2 decrease.

[0034]

According to the present invention, light waves of two different wavelengths are used, one light wave is linearly polarized and passed through a Faraday element, and then separated into a P polarization component and an S polarization component, and the other light wave is After passing through the same path as the light wave except for the Faraday element, it is separated into a P polarized light component and an S polarized light component,
These four signals are processed and a signal proportional to the rotation angle of the Faraday element is extracted, so even if there are fluctuations in the light intensity due to the light source or each optical signal transmission, an output that eliminates the effects of these changes can be obtained, improving accuracy. It has the effect of being able to measure direct current with good quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main configuration of a first embodiment of the present invention.

2 is a sectional view and a partial side view showing details of a Faraday element light input/output section in the embodiment of FIG. 1; FIG.

FIG. 3 is a block diagram showing a configuration example of a signal processing circuit in the embodiment of FIG. 1;

FIG. 4 is a block diagram showing the main configuration of a second embodiment of the present invention.

FIG. 5 is a block diagram showing the main configuration of a third embodiment of the present invention.

[Explanation of symbols]

1, 2 Light sources 3, 4 Optical fiber 5 Polarizer 6 Faraday element 7 Analyzer 8, 9 Optical fibers 10, 11 Optical demultiplexer 12, 13, 14, 15 Photodiode 12A,
14A Photoelectric converter 16', 16'' Prism 17 Dichroic (optical filter) 18 Optical multiplexer 20 Arithmetic processing circuit 30 Signal processing circuit 31, 32, 33, 34 Amplifier 35, 36, 39 Divider 37 Addition circuit 38 Subtraction Circuit 39A Sum-difference circuit 40A, 40C Low-pass filter 40B, 40D High-pass filter

Claims (3)

[Claims] 1. A light source that generates a constant output light, a polarizer that linearly polarizes the light emitted from the light source, a medium that has a magneto-optical effect and is placed around a current conductor to be measured, and a In an optical current transformer comprising a signal processing circuit that converts photons and optical signals emitted from the photons into electrical signals, and performs arithmetic and processing, the light source includes a light source that emits a light wave with a wavelength λ1, and a light source that emits a light wave with a wavelength λ2. a light source, a means for transmitting a light wave with a wavelength λ1 through the medium having a magneto-optic effect so as to surround the current conductor to be measured, and a means for transmitting a light wave having a wavelength λ1 through the medium so as to prevent the light wave having a wavelength λ2 from passing through the medium. means for splitting at an entrance; means for combining a light wave with a wavelength λ1 that has passed through the medium and a light wave with a wavelength λ2 that has not passed through the medium, and then separating the light wave into a P-polarized light component and an S-polarized light component; A transmission path for transmitting the polarized light component and the S polarized light component, means for separating the transmitted P polarized light component and the S polarized light component into wavelengths λ1 and λ2, respectively, and sum-difference calculation of the separated optical output signals. An optical DC current transformer characterized by comprising a signal processing circuit which obtains an electrical output signal of the same polarity as the current to be measured through processing. 2. An optical multiplexer that superimposes a light wave emitted from a light source that emits a light wave with a wavelength λ1 and a light wave that is emitted from a light source that emits a light wave with a wavelength λ2; an optical fiber that leads to a medium having a wavelength of The optical DC current transformer according to claim 1, characterized in that: 3. Means for making λ1 and λ2 the same wavelength and superimposing a high frequency on the light that does not pass through a medium having a magneto-optic effect, and photoelectrically converting the P polarized light component and the S polarized light component output from the analyzer. 2. The method according to claim 1, further comprising a photoelectric conversion means for separating the output of the photoelectric conversion means into a direct current component and an alternating current component, and an arithmetic circuit for processing the output of the separation means. The optical application DC current transformer described.