JP3131011B2 - Photocurrent transformer for DC - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocurrent transformer used for measuring DC current, and more particularly to a DC photocurrent transformer suitable for power equipment.

2. Description of the Related Art As a direct current measuring device, a low voltage ammeter such as a moving coil type is well known. By the way, in response to the recent rapid increase in power demand, for example, surplus power generated in the west of Kanto is supplied to the Kanto area, and at this time, the frequency of the generated power is different. Therefore, AC is converted to DC once, and then frequency-converted by inverters and sent to substations. In such a case, it is necessary to measure the direct current. However, in the measurement of DC current in such a power system, for example, even if the above-described ammeter is modified for high voltage and used, even if the ammeter is installed in series with the power system, the If any trouble occurs, it cannot be adopted because the power system may be disconnected. That is, in the measurement of the DC current of the power system, there is a special circumstance that the current must be able to be measured while being separated from the power system. For this reason, in the past, as a current measuring device in a power system, a Kramer type current transformer using a saturable reactor was employed, but such a type of current transformer includes an excitation such as a motor generator. Since an AC uninterruptible power supply is required, the device becomes large and the operation becomes complicated.
In addition, there is a problem in accuracy and response speed with respect to a small measurement amount, and there is also a problem that a maintenance burden is large.
Therefore, the present inventors have proposed a current transformer in which such a problem is solved in Japanese Patent Application No. 3-335284.
The current transformer according to this application is a polarizer that transmits light emitted from a light source while aligning the light with a predetermined polarization plane, and is disposed facing the same optical axis as the polarizer, and the polarization plane of the polarizer. An analyzer that transmits light having a different polarization plane, a light receiving element that receives the transmitted light of the analyzer and converts the light into an electric signal, and provided on the optical axis between the polarizer and the analyzer. A pair of Faraday rotators, a modulation coil wound around one of the outer circumferences of these Faraday rotators and supplied with an alternating current, and a modulation coil wound around the other outer circumference of the Faraday rotator. The power line is supplied, and a signal processing unit for obtaining a value corresponding to the Faraday rotation angle of the one Faraday rotator based on the measured current from the electric signal converted by the light receiving element. However,
In the current transformer having such a configuration, although the problem of the Kramer-type current transformer is solved, there are also technical problems described below.

That is, in the current transformer according to the above-mentioned application, a Faraday rotator to which a magnetic field is applied by a current to be measured and a Faraday rotator to which a magnetic field is applied by an alternating current for modulation are arranged close to each other. There is a need to. However, when such an arrangement is to be ensured in an actual power facility, an electric circuit for applying a modulation current comes close to a high-voltage charging unit. For example, in a GIS facility, electrical insulation may be secured. It was difficult. The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a DC photocurrent transformer in which electrical insulation is easily ensured in actual power equipment. Is to do.

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a polarizer on which a composite wave of two lights having different wavelengths is incident, and a polarizer provided behind the polarizer and having a current to be measured. A Faraday element to which a magnetic field is applied, and a polarization separation element that is provided behind the Faraday element and separates light that has passed through the Faraday element into two polarization components;
A pair of photoelectric conversion elements for converting two lights separated by the polarization separation element into an electric signal, and extracting the light amount of each wavelength of the composite wave from the electric signal converted by the photoelectric conversion element, is extracted. A calculator for calculating a Faraday rotation angle by applying the magnetic field from the amount of light , wherein the combined wave is
Into a pair of fluorescent optical fibers with fluorescent components of different wavelengths
Projecting light emitted from at least one light source
And the polarization splitting element has two surfaces parallel to each other.
And a pair of polarizers.
It is characterized by doing. The fluorescent optical fiber transmits light.
A first fluorescent light filter having a red phosphor on the front side in the excessive direction;
The first fluorescent fiber has a green
Connecting a second fluorescent optical fiber having a phosphor
it can.

According to the DC photocurrent transformer having the above-described configuration, if a Faraday element to which a magnetic field is applied by a current to be measured is installed in, for example, GIS equipment, a composite wave having a different wavelength is used as a polarizer. Since the light enters through the Faraday element and passes through the Faraday element, the light is received by the polarization splitting element. Therefore, these parts are constituted only by a complete optical system, and electrical insulation is easily secured. Also, in the present invention, different wavelengths
Since the centers of the beam widths of the two light sources almost coincide,
Constant accuracy is improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is similar to the present invention .
Measuring the magnitude of the current using two different wavelengths of light
FIG. 4 is an explanatory diagram of a measurement principle of a DC photocurrent transformer. The DC photocurrent transformer shown in FIG. 1 includes a polarizer 1, a Faraday element 2, a polarization separation element 3, a pair of photoelectric conversion elements 4 and 5, an arithmetic unit 6, which are installed on the same optical axis. have. The polarizer 1 receives a combined wave of two lights having different wavelengths, and transmits the combined wave as linearly polarized light. In this embodiment, as for the composite wave, the light of wavelength λ ₁ emitted from the light source 7 and the light of wavelength λ ₂ emitted from the light source 8 are introduced into the multiplexer 9 by an optical fiber, and It is generated by merging inside. The Faraday element 2 applies a Faraday rotation that is inversely proportional to the square of the wavelength to light passing through the inside thereof, and a coil through which a current to be measured flows is wound around the outer periphery. Can be The polarization separation element 3
For example, it is composed of a lotion prism, a beam splitter, and the like, and separates the light passing through the Faraday element 2 into two orthogonal polarization components. The pair of photoelectric conversion elements 4 and 5 receive the two lights separated by the polarization splitting element 3 through the optical fiber 10, respectively, and convert the introduced lights into electric signals. The arithmetic unit 6 includes the photoelectric conversion elements 4 and
5, the wavelengths λ ₁ and λ _{2 of the} composite wave
The Faraday rotation angle due to the application of the magnetic field H is calculated from the extracted light quantity. Now, light source 7,
8, the light amount of the light of wavelength λ ₁ that has passed through the polarizer 1 is P ₀₁ , the light amount of the light of the same wavelength λ ₂ is P ₀₂ , and the output of the photoelectric conversion elements 4 and 5 has the wavelength λ ₁ light amount P _1X of wavelength components, a P _1Y, amount of wavelength components of the lambda ₂ is P
_2X , P _2Y , Faraday rotation angle of wavelength λ ₁ is θ ₁ , wavelength λ ₂
Assuming that the Faraday rotation angle is θ ₂ and θ ₁ , θ ₂ ≪π / 4, the following relational expression is established in the transformer of FIG. P _1X = αP ₀₁ α _x (1 + 2θ ₁ ) (1-a) P _2X = αP ₀₂ α _x (1 + 2θ ₂ ) (1-b) P _1y = αP ₀₁ α _y (1-2θ ₁ ) (1-c) P _2y = αP ₀₂ α _y (1-2θ ₂ ) (1-d) θ ₂ = rθ ₁ where r is the ratio of the Faraday rotation angle of the two lights,
α is a coefficient representing the loss from the polarizer 1 to the polarization splitter 3, and α _X and α _Y are the polarization splitter 3 to the photoelectric converter 4,
Coefficients representing losses up to 5. By transforming equation (1), the output S is a function of only θ ₁ and r (ratio of θ ₁ and θ ₂ ) as shown below, using measurable values P _1X , P _1Y , P _2X , and P _2Y. Is obtained. _{S = {(P 2Y / P} 1Y) / (P 2X / P 1X)} - 1 (2-a) S = {4 (1-r) θ 1} / {1-2 (1-r) θ 1 -4rθ ₁ ^{2 (2-b)} _{Accordingly, P 1X, P 1Y, P} 2X, by measuring the P _2Y (2-a)
Calculates the S based on the equation, by obtaining a theta ₁ based from this value (2-b) wherein the magnetic field H the theta ₁ is due to the measured current
And the wavelength λ ₁ , and the wavelength λ ₁ is known, so that the magnitude of the current to be measured is known. FIG. 2 shows a first embodiment of a DC photocurrent transformer according to the present invention. The embodiment shown in the figure differs from the measurement principle diagram shown in FIG. 1 in a portion for generating a synthetic wave and a polarization splitting element 11. The part that generates the composite wave is a pair of first and second fluorescent optical fibers 12 and 13.
Is used. The first fluorescent optical fiber 12 contains a red phosphor and is disposed on the front side in the light transmission direction. The second fluorescent optical fiber 13 contains a green phosphor, and
4 is connected to the rear end of the first fluorescent optical fiber 12. A normal plastic fiber 15 is connected to the rear end of the second fluorescent optical fiber 13 via an optical connector 14.
6 are arranged. In this embodiment, a pair of fluorescent lamps 17 are used as the light sources for the fluorescent optical fibers 12 and 13. However, the number of the fluorescent lamp light sources may be one. Light may enter from the opening end of one fluorescent optical fiber 12. On the other hand, the polarization splitting element 11 is composed of a thin flat glass plate 11a that is installed to be inclined behind the Faraday element 2, and this glass plate 11a.
Pair of polarizers 11b and 11 that receive transmitted light and reflected light
c. In the DC photocurrent transformer configured as described above, the magnetic field H due to the measured current is applied.
The Faraday element 2 to be installed, for example, in a GIS facility
Then, the combined waves having different wavelengths are added to the light via the polarizer 1.
Incident on the Faraday element 2 and the polarization separation element
Child 3 and these parts are completely optical
It is composed of only the system, and electrical insulation is easily secured.
To measure the magnitude of the measured current with high accuracy
Can be. This effect was found based on the following experiment. In this experiment, first, in the transformer of FIG.
The state of the composite wave incident on the Faraday element 2 was measured. The experimental conditions were as follows.
Using an ED and an LED having a wavelength of 660 nm, the cross-sectional intensity of the outgoing beam of the light transmitting side optical fiber (plastic fiber having a core diameter of 200 μm) was measured at a position 2.5 cm from the end face. FIG. 3 shows the measurement results. As is clear from the measurement results shown in this figure, it was found that the intensity distributions for the two wavelengths were different. If the intensity distributions are different as described above, the coupling between the two lights is generally not equal, and the measurement accuracy is reduced. Here, when the cause of the difference in the intensity distribution was examined, it is supposed that the difference was due to the different light incident conditions on the fiber. This is inferred from the fact that the same LED changes the beam intensity by changing the angle and position of the incident end face of the optical fiber, and also changes the distribution by applying force to the side of the optical fiber. Was. Therefore, as a countermeasure against this problem, a fluorescent optical fiber that contains a phosphor inside the core and has a function of converting light incident from the side surface into a transmissible fluorescent light has been devised. FIG. 4 shows a result of connecting a fluorescent optical fiber having a diameter of 1 mm to a plastic fiber having a diameter of 1 mm and measuring the intensity distribution of the output beam at a position 1 cm from the end face. In this case, the change in the intensity distribution was small even when the type of the fluorescent optical fiber to be connected was changed. It is considered that such a result is obtained because the fluorescence generated in the fluorescent optical fiber has no directivity.
Next, an experiment for confirming the function of the lotion prism as the polarization separation element 3 was performed. FIG. 5 shows a main part of the experiment, in which two LED lights (880 nm and 660 nm) emitted from a common fiber are incident on a lotion prism (calcite, a separation angle of 15 degrees), and the beam cross section of the extraordinary ray is shown. The intensity distribution was measured 16 cm away from the prism. FIG. 6 shows the measurement results. The results show that the centers of the two beam widths are shifted because the refraction angles at the joining surfaces in the prisms are different. Such a phenomenon did not occur for the ordinary beam. This problem is caused by refraction, and could not be solved by using another polarization splitting element with refraction. Then, the polarization separation element 11 as shown in FIG. 7 was devised. The polarized light separating element 11 includes one thin glass plate 11a and a pair of polarizers 11b and 11c.
According to this configuration , the glass plate 1
Since 1a is thin and both sides are parallel, the beam passing through the plate 11a is parallel, and a slight displacement occurs. FIG. 8 shows the measurement result of the intensity distribution of the reflected light beam. In this measurement, a 1 mm thick glass plate 11 was used.
A light beam was incident on a at an incident angle of 67 degrees, and the cross-sectional strength was measured at a position 12 cm away from the glass plate 11a. As is clear from the results shown in this figure, no deviation was recognized at the center of the two beam widths . That is, the measurement results shown in FIG.
As a result, the width of the beam of light having a wavelength of 660 nm is
Is about 0 mm to about 19 mm, but the wavelength is 88 mm.
The width of the 0 nm light beam is about 1 mm to about 2 mm at the measurement position.
0mm, the beam width of light with a wavelength of 880nm
Is at the center of the width of the beam of light having a wavelength of 660 nm.
On the other hand, it is shifted by about 1 mm. However, FIG.
In the measurement results obtained, there was no such a significant deviation between the two.
The centers of the beam widths of two lights with different wavelengths are almost the same
are doing. Here, in the configuration using the glass plate 11a,
Although the loss of light for p-polarized light and that for s-polarized light are different, this can be considered to be included in the losses α _X and α _Y shown in the above equation 1, and in equation 2, these losses are eliminated. It does not affect the measurement of. Based on the above experimental results, a DC current was actually passed through a coil wound around the Faraday element 2 with the DC photocurrent transformer having the configuration shown in FIG. The experiment conditions were the same as those in the above experiments, and in order to minimize the influence of the problem of the intensity distribution of the beam cross section, after sufficiently adjusting the optical axis and the focus of the light incident on the fiber on the light receiving side, θ ₁ (Wavelength 880 nm) =-4.2
° to + 4.2 °. FIG. 9 shows the measured values of the _amounts of emitted light P _1X , P _1Y , P _2X , and P _2Y of the light receiving fiber according to the formula (2-
The relationship between the value of S obtained by substituting into (a) and θ ₁ is expressed by equation (2).
This is shown together with the theoretical curve obtained from b). As is clear from the results shown in the figure, it is understood that the optical transformer shown in FIG. 2 can perform a measurement close to the theoretical value. In addition, above
In the above embodiment, a pair of fluorescent light
A thin flat plate is used for the polarization separation element 11 using fibers 12 and 13.
Although the case where the glass plate 11a in a shape of is used is illustrated, the present invention
Then, it is not necessary to use both at the same time.
Even if they are used individually, the corresponding effects
can get.

As described above in detail in the embodiments,
According to the photocurrent transformer for direct current according to the present invention, only the optical system is directly installed in the actual power equipment,
Electrical insulation can be easily performed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a measurement principle of an optical transformer according to the present invention.

FIG. 2 shows a first embodiment of the optical transformer according to the present invention .
FIG.

FIG. 3 is an intensity distribution characteristic diagram of an optical fiber.

FIG. 4 is an intensity distribution characteristic diagram of a fluorescent optical fiber.

FIG. 5 is an explanatory diagram of a polarization splitting element used in a conventional optical transformer.

FIG. 6 is a characteristic diagram of the polarization separation element shown in FIG.

[7] of the polarization separating element used in an optical transformer of the present invention
It is a description view.

FIG. 8 is a characteristic diagram of the polarization separation element shown in FIG.

9 is a graph showing a current measurement result of the optical transformer shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polarizer 2 Faraday element 3,11 Polarization separation element 4,5 Photoelectric conversion element 6 Operation unit 7,8 Light source 9 Combiner

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tetsuo Hirano 460 Momokasa, Hino-shi, Tokyo Tokyo Electric Power Company, Toden Gakuen (56) References JP-A-63-118677 (JP, A) JP-A-61-26875 (JP, A) JP-A-56-29174 (JP, A) JP-A-1-302330 (JP, A) JP-A-61-182553 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ G01R 19/00-19/32 G01R 15/24 G01R 33/032

Claims (2)

(57) [Claims] 1. A polarizer on which a synthetic wave of two lights having different wavelengths is incident, a Faraday element provided behind the polarizer and to which a magnetic field by a current to be measured is applied, and a Faraday element provided behind the Faraday element A polarization separation element that separates the light that has passed through the Faraday element into two polarization components;
A pair of photoelectric conversion elements for converting two lights separated by the polarization separation element into an electric signal, and extracting the light amount of each wavelength of the composite wave from the electric signal converted by the photoelectric conversion element, is extracted. A calculator for calculating a Faraday rotation angle by applying the magnetic field from the amount of light , wherein the composite wave has a pair of fluorescent components having different wavelengths.
Fluorescent optical fiber fired from at least one light source
The polarized light separating element is formed by projecting light, and the polarized light separating element is a thin flat plate having two parallel surfaces.
A photocurrent transformer for direct current , comprising a glass plate having a shape of a circle and a pair of polarizers . 2. The optical fiber according to claim 1, wherein the fluorescent optical fiber has a light transmitting direction.
A first fluorescent optical fiber having a red phosphor on the front side of
A green phosphor is disposed at the rear end of the first fluorescent fiber.
That the second fluorescent optical fiber having
The DC photocurrent transformer according to claim 1, wherein