JPH09318675A - Photoelectric current transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase measuring sensitivity so as to miniaturize and make thin a transformer, to reduce the leakage of a magnetic flux to a minimum so as to increase measuring accuracy and to eliminate crosstalk caused by a leaked magnetic flux caused by intersection with other lines. SOLUTION: A photoelectric current transformer is a multiple reflection type photoelectric current transformer. In other words, a magnetic optical element 14 having a reflection films 15-1 and 15-2 formed in its upper and lower surfaces is disposed in the gap 20-1 of a core 20. The magnetic optical element 14 is made of a garnet artificial crystal (YIG) mainly containing yttrium, iron and oxygen. The reflection films 15-1 and 15-2 are, for example aluminum vapor deposited films.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocurrent transformer suitable for non-contact measurement of a current flowing through a high voltage electric wire over a coating.

[0002]

2. Description of the Related Art When a magnetic field is applied to a magneto-optical element such as lead glass from the outside and polarized light is transmitted in the same direction as the magnetic field, the plane of polarization of polarized light rotates in proportion to the strength of the magnetic field while passing through the element. . This is called the Faraday effect. This rotation angle φ can be expressed as φ = V · H · L ... (1). Here, H is the strength of the applied magnetic field, L is the optical path length in the magneto-optical element, and V is the Verdet constant. The Verdet constant is a constant peculiar to the magneto-optical element and indicates the magnitude of the Faraday effect.

As a photocurrent transformer utilizing the Faraday effect, there is a through-type photocurrent transformer whose main part is shown in FIG. In the figure, 1 is an optical fiber, 2 is an optical lens, 3 is a polarizer, 4 is a magneto-optical element, 5 is an analyzer,
6 is an optical lens, 7 is an optical fiber, 8 is a core (iron core),
9 is a high voltage electric wire located in the hollow portion of the core 8. The magneto-optical element 4 is made of lead glass and has a gap 8 in the core 8.
It is located between -1.

In this photocurrent transformer, light P _in from a light source (not shown) such as a light emitting diode is transmitted by an optical fiber 1, is condensed by an optical lens 2, and is polarized by a polarizer 3.
After being polarized (linearly polarized) by, the light is incident in the length direction of the magneto-optical element 4. If a magnetic field exists in the length direction of the magneto-optical element 4, the polarization plane of the polarized light incident on the magneto-optical element 4 rotates in proportion to the product of the strength of the magnetic field and the optical path length in the magneto-optical element 4. To do.

This rotation angle φ of the plane of polarization is detected as a change in light quantity by the analyzer 5 to which an optical bias of 45 ° is applied,
It is guided to a photoelectric conversion device (not shown) by the optical lens 6 and the optical fiber 7, converted into an electric signal to measure the strength of the magnetic field, and is positioned in the hollow portion of the core 8 based on the measured strength of the magnetic field. The current flowing through the high voltage electric wire 9 is measured.

[0006]

However, according to such a conventional photocurrent transformer, in order to increase the measurement sensitivity, the size of the magneto-optical element 4 in the direction of the optical axis must be lengthened, and the size of the magneto-optical element 4 must be small. Thinning is difficult. Further, since the magneto-optical element 4 is made of lead glass, a part of the magnetic flux passing through the core 8 leaks in the gap 8-1 and does not act on the magneto-optical element 4. Therefore, the measurement accuracy decreases. Further, when the high-voltage electric wire of the other phase is short-circuited (short-circuit accident), the leakage magnetic flux interlinking from the high-voltage electric wire of the other phase (other wire) acts on the magneto-optical element 4 as crosstalk, and the measurement is performed. It has an adverse effect as an error.

The present invention has been made in order to solve such a problem, and an object thereof is to increase the measurement sensitivity, to make it compact and thin, and to reduce the leakage flux. It is an object of the present invention to provide a photocurrent transformer capable of improving the measurement accuracy and removing crosstalk due to the leakage magnetic flux which is crossed from another line.

[0008]

In order to achieve such an object, the first invention (the invention according to claim 1) is a multiple reflection type photocurrent transformer and is arranged between the core gaps. The magneto-optical element is a garnet-like artificial crystal (YIG) containing yttrium, iron and oxygen as main components. According to the present invention, the optical path length is increased by the multiple reflection of light within the magneto-optical element. Further, by making the magneto-optical element an artificial crystal containing iron, that is, an artificial crystal that does not give a loss to the magnetic circuit, the leakage magnetic flux between the core gaps becomes small.

The second invention (the invention according to claim 2) is the first invention.
In the invention, the magneto-optical element is Y ₃ Fe ₅ O ₁₂ . A third invention (the invention according to claim 3) is the same as the first invention, except that the magneto-optical element is Y ₂ Bi ₁ Fe ₅ O ₁₂ . A fourth invention (the invention according to claim 4) is the first, second, and third inventions, wherein the reflective film for multiple reflection of polarized light in the magneto-optical element is a high-permeability body. According to the present invention, the leakage of magnetic flux in the reflective film is smaller than that in the case where the reflective film is a dielectric multilayer film.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on embodiments. FIG. 1 is a diagram showing a main part of a photocurrent transformer according to an embodiment of the present invention. In the figure,
10 is an optical fiber, 11 is an optical lens, 12 is a polarizer,
Reference numeral 13 is an optical prism (first prism), 14 is a magneto-optical element, 15-1 and 15-2 are reflection films deposited on the upper and lower surfaces of the magneto-optical element 14, and 16 is an optical prism (second prism). ), 17 is an analyzer, 18 is an optical lens, 19 is an optical fiber, 20 is a core (iron core), 21
Is a high-voltage electric wire located in the hollow portion of the core 20.

The magneto-optical element 14 is a garnet-like artificial crystal composed mainly of yttrium, iron and oxygen, that is, Y.
IG (Yttrium Iron Garnet), reflective film 15-
It is arranged between the gaps 20-1 of the core 20 with the surface on which 1 and 15-2 are formed as the vertical direction.

In this embodiment, the magneto-optical element 1
4, specifically, the molecular formula thereof is Y ₃ Fe ₅ O ₁₂
It is manufactured by making a YIG bulk and cutting it out. The reflection films 15-1 and 15-2 are, for example, aluminum vapor deposition films. In addition, the magneto-optical element 1
The size of 4 is 3x3x40mm or 5x5x40mm
Or, in combination with the core 20, the optimum size is determined.

In this photocurrent transformer, light P _in from a light source (not shown) such as a light emitting diode is supplied to the optical fiber 10.
Is transmitted by the optical lens 11, is condensed by the optical lens 11, is polarized (linearly polarized) by the polarizer 12, and then is incident in the thickness direction of the magneto-optical element 14 via the optical prism 13. Then, the polarized light incident on the magneto-optical element 11 is multiple-reflected in the element and then taken out from the optical prism 16.

In this case, the polarization plane of the polarized light extracted from the optical prism 16 is the reflection surface 15- of the magneto-optical element 14.
If a magnetic field exists in the direction orthogonal to 1 and 15-2,
It rotates in proportion to the product of the strength of this magnetic field and the effective optical path length in the magneto-optical element 14.

The rotation angle φ of the plane of polarization is detected as a change in the amount of light by an analyzer 17 to which an optical bias of 45 ° is applied, and is guided to a photoelectric conversion device (not shown) by an optical lens 18 and an optical fiber 19. The strength of the magnetic field (the magnetic field due to the current flowing through the high-voltage electric wire 21) is measured by converting it into an electric signal, and the current flowing through the high-voltage electric wire 21 located in the hollow portion of the core 20 is measured from the measured strength of the magnetic field. To do.

According to this method, the optical path length increases due to the multiple reflection of light within the magneto-optical element 14. As a result, the measurement sensitivity is increased by the length of the optical path, and it is possible to make the device compact and thin. Further, according to this method, since the magneto-optical element 14 is an artificial crystal containing iron, that is, an artificial crystal that does not give a loss to the magnetic circuit, the leakage magnetic flux between the gap 20-1 of the core 20 is small. Therefore, it is possible to improve the measurement accuracy and remove the crosstalk due to the leakage magnetic flux that intersects with another line.

FIG. 2 shows the relationship between the interval δ of the gap 20-1 and the indicated current value I when the magneto-optical element 14 is YIG and when it is lead glass. Characteristic I shown in the same figure is when the magneto-optical element 14 is YIG, and characteristic II is when the magneto-optical element 14 is lead glass. The characteristic III shown as a reference in FIG. 2 is a case where a general current transformer (see FIG. 4) including a core (closed core) and a winding is used.
From this characteristic, it can be seen that the measurement error is smaller when the magneto-optical element 14 is YIG than when it is lead glass. Further, the crosstalk due to the leakage magnetic flux which is cross-linked from the other line is almost the same in the characteristic I and the characteristic III, but it is actually measured that the characteristic II picks up the cross-linked magnetic flux of two digits or more.

In the above-described embodiment, the magneto-optical element 14 is Y ₃ Fe ₅ O ₁₂ , but Y ₂ Bi ₁ Fe _{5 is used.}
It may be O ₁₂ . That is, its molecular formula is Y ₂ Bi ₁
The magneto-optical element 14 may be manufactured by forming a YIG bulk containing Fe ₅ O ₁₂ and cutting it out.

The magneto-optical element 14 is replaced with Y ₂ Bi ₁ Fe ₅ O ₁₂
, The wavelength λ of the light used is 500 nm
Absorption is a little higher at (visible light), but 800 ~
The results show that at 850 nm (near infrared light), the absorption is small, the Verdet constant is large, and the Faraday rotation is the same as visible light. Moreover, it was experimentally confirmed that the absorption attenuation of Y ₂ Bi ₁ Fe ₅ O ₁₂ can be used in a small region.

Further, in the above-described embodiment, the reflection film 1
Although 5-1 and 15-2 are vapor-deposited films of aluminum, other metals such as gold, silver, and copper may be formed by vapor deposition or sputtering. Reflective films 15-1 and 1
If 5-2 is aluminum + nickel, aluminum + iron, etc.,
That is, if a high-permeability body is used, the leakage of magnetic flux in the reflective films 15-1 and 15-2 can be further reduced. The reflection films 15-1 and 15-2 do not necessarily have to be high magnetic permeability bodies, and the reflection films 15-1 and 1
Although there is some leakage of magnetic flux at 5-2, a dielectric multilayer film that is optimal for the wavelength λ of the light used may be used. Further, the vapor deposition film of aluminum may be provided with a SiO ₂ film so as not to be further oxidized. Good results have also been obtained with a reflective film of aluminum + SiO ₂ .

Further, in the above-described embodiment, the current flowing through the high voltage electric wire 21 is measured, but the object for measuring the current is not limited to the high voltage electric wire. Since the photocurrent transformer of the present invention has a very high measurement sensitivity, it can be increased in sensitivity and can measure from harmonics focusing on the current waveform to high frequencies. As a result, it is possible to identify a location (high-frequency generation source) where high-frequency waves are flowing out, such as an electric work and a factory.

[0022]

As is apparent from the above description, according to the present invention, the optical path length is increased by the multiple reflection of light in the magneto-optical element, and the measurement sensitivity is increased by the optical path length. And it becomes possible to make it thinner. Also, by using an artificial crystal containing iron as the magneto-optical element, that is, an artificial crystal that does not give a loss to the magnetic circuit, the leakage flux between the gaps of the core becomes small, improving the measurement accuracy and other wires. It is possible to eliminate the crosstalk due to the leakage magnetic fluxes that intersect with each other.

[Brief description of drawings]

FIG. 1 is a diagram showing a main part of a photocurrent transformer according to an embodiment of the present invention.

FIG. 2 shows a Y-type magneto-optical element in this photocurrent transformer.
It is a figure which shows the relationship between the gap space (delta) and marking current value I when it is set to IG and lead glass.

FIG. 3 is a diagram showing a main part of a conventional photocurrent transformer.

FIG. 4 is a diagram showing a general current transformer including a core (closed core) and a winding.

[Explanation of symbols]

10 ... Optical fiber, 11 ... Optical lens, 12 ... Polarizer,
13 ... Optical prism (first prism), 14 ... Magneto-optical element, 15-1, 15-2 ... Reflective film, 16 ... Optical prism (second prism), 17 ... Analyzer, 18 ... Optical lens, 19 … Optical fiber, 20… Core (iron core), 21…
High voltage wire.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jun Sato 15 Sakanoshita, Date-cho, Date-gun, Fukushima Prefecture Asahi Denko Co., Ltd. (72) Tetsuro Yoshida 15 Sakanoshita, Date-cho, Date-gun, Fukushima Prefecture Asahi Denko Co. (72) Inventor Sakae Watanabe 15 Sakanoshita, Date-cho, Date-gun, Fukushima Prefecture Asahi Electric Co., Ltd. (72) Inventor Yutaka Ono 4-5-1 Sagimiya, Nakano-ku, Tokyo (72) Toshihiko Yoshino Urayasu, Chiba Prefecture 3-4-12 Maihama

Claims (4)

[Claims] 1. A magneto-optical element is disposed between the core gaps, polarized light is incident on the magneto-optical element, multiple-reflected polarized light is extracted in the magneto-optical element, and a rotation angle of a polarization plane of the extracted polarized light. Is a photocurrent transformer that measures a magnetic field applied to the magneto-optical element based on the above, and measures the current flowing through the electric wire located in the hollow portion of the core from the measured magnetic field, wherein the magneto-optical element is yttrium and iron. A photocurrent transformer characterized by being a garnet-shaped artificial crystal containing oxygen and oxygen as main components. 2. The photocurrent transformer according to claim 1, wherein the magneto-optical element is an artificial crystal having a molecular formula of Y ₃ Fe ₅ O ₁₂ . 3. The photocurrent transformer according to claim 1, wherein the magneto-optical element is an artificial crystal having a molecular formula of Y ₂ Bi ₁ Fe ₅ O ₁₂ . 4. The photocurrent transformer according to claim 1, wherein the reflective film for multiply-reflecting the polarized light in the magneto-optical element is a high magnetic permeability body.