JP2715145B2 - Optical current transformer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical current transformer, and more particularly to a circular integral type suitable for measuring a current flowing in a high-voltage conductor with high accuracy by utilizing the Faraday effect. It relates to an optical current transformer.

[Conventional technology]

FIG. 5 shows an example of such a conventional circuit-integrated optical current transformer. In the figure, a magnetic field H is generated by a current I flowing through a conductor 1. At this time, linearly polarized light passes through the conductor 1 along the internal optical path L of a glass having a Faraday effect (hereinafter referred to as a Faraday effect element 2) such as lead glass arranged so as to interlink with the conductor 1. Then, the polarization plane of the light is rotated by an angle θ = V · H · L (where V is a Verde constant, H is the strength of the magnetic field in the light traveling direction, L is the optical path length in the Faraday element). When the strength of a magnetic field along an arbitrary closed curve generated around the conductor 1 by the current I is circularly integrated, a formula of the so-called Ampere circuit law, I = φH · dL, is established. Therefore, when light is circulated in the Faraday effect element, I = (1 / V) Δθ · dL.

As described above, by integrating the Faraday rotation angle generated by circling light so as to interlink with the conductor 1, the magnetic field intensity H for the entire magnetic path of the conductor itself can be accurately detected. The current I flowing through the conductor 1 can be measured with high accuracy.

FIG. 6 is a plan view showing the orbital optical path L in FIG. 5 in detail. In the orbital integral path closed loop which is a complete orbital integral type, the incoming and outgoing light intersect at a point 0, but the linearly polarized light portion is 0-ab-
If it exists only in the closed loop of c-0, the magnetic field intensity received by the linearly polarized light portion is constant regardless of the position of the self-phase conductor 1 in the through hole φ, and the current flowing through the conductor 1 is It will be possible to measure with high accuracy. In addition, it is hardly affected by the other-phase magnetic field.

FIG. 7 shows an arrangement in which the Faraday effect element 2 is arranged so as to interlink with the conductor 1, and a part of the element 2 that makes the linearly polarized light A circulate around the conductor 1 is deleted. In this configuration, the linearly polarized incoming / outgoing light intersects at the intersection 0 in the space. Further, the polarizer 7 for inputting the linearly polarized light A to the element 2 and the analyzer 8 are separated from each other, for example, a sheath 13 of a GIS (gas insulated switchgear).
Are located in In this configuration, the linearly polarized light A obtained through the polarizer 7 is transmitted to dabcg. And the spatial transmission unit, which is not affected by the magnetic field,
▼ ′ and ▲ ▼, and the Faraday effect element 2 alone forms a closed loop of 0abc0, and the ▲ ▼ ′ and ▲ ▼ ″ portions before the element 2 are partially deleted become a space. You will gain accuracy.

[Problems to be solved by the invention]

However, in the conventional circulating-integrated optical current transformer shown in FIG. 5, both the polarizer 7 and the analyzer 8 using the polarization beam splitter (PBS) are arranged outside the Faraday effect element 2. Configuration. This means that the linear polarization part is rotated by the magnetic field, and the linear polarization part is occupied by the optical path from the central part of the polarizer 7 to the central part of the analyzer 8, and the linear polarization part is extended to outside the closed loop of the circuit. Will be.

That is, in FIG. 6, the linearly polarized light portion affected by the magnetic field also exists in the arrows ▲ and ▼.

Therefore, the magnetic field intensity received by the linearly polarized light portions of ▲ and ▼ changes depending on different positions of the self-phase conductor 1 in the through hole φ.

This change affects the rotation of the polarization plane of the light, and the measurement accuracy of the current I flowing through the conductor 1 decreases. The error amounts to several percent, and for example, it is not possible to clear the JEC-1201-scale population class of current transformers for substation protection. The largest defect is easily affected by the other-phase magnetic field. In particular, in the case of the three-phase type, the adjacent other-field magnetic field cannot be avoided. Since this error affects not the ratio of the length of the optical path length in the Faraday effect element but the absolute value of the magnetic field of the other phase, there is a risk that an unpredictable large error may occur.

7, the polarizer 7 for obtaining the linearly polarized light A and the linearly polarized light that has been subjected to Faraday rotation by the Faraday effect element 2 by the magnetic field are branched and converted into an optical output. The photon 8 is indispensable and has a finite length for spatial transmission. For example, in the Faraday effect element 2 arranged in the GIS, the location of the polarizer and analyzer depends on the distance to the sheath 13. . During this time, it is the place most susceptible to the other-phase magnetic field. Therefore, the linearly polarized portion between the triangle in the polarizer 7 and the triangle in the analyzer 8 is affected by the self-phase conductor 1 and the other-phase magnetic field. That is, the polarizer 7 and the analyzer 8 also have a function as a photocurrent sensor, and it becomes impossible to measure an accurate current of the self-phase conductor 1. Also, in the Faraday effect element 2,
I = (1 / V) Δθ · dL, and L is ▲ ▼ ′ and ▲ ▼ ′
Not only is the space shortened due to spatial transmission, the measurement sensitivity is reduced, but this configuration is always limited to only the spatial transmission method, which causes various problems such as the spread of spatial light, axial misalignment, and contamination of the lens surface. There was a problem with the functional accuracy as a photocurrent sensor.

Therefore, the present invention has been made based on such circumstances, and an object of the present invention is to reduce the influence of a magnetic field of another phase remarkably, and to achieve highly accurate and stable measurement of light. To provide a current transformer.

[Means for solving the problem]

In order to achieve such an object, the present invention enters light through a polarizer into a Faraday effect element installed around a conductor, and after going around the conductor, emits light from the Faraday effect element. In an optical current transformer that extracts light as an amount of light by an analyzer and measures a current in the conductor, the polarizer and the analyzer look at the light passage portion from the running direction of the conductor, and inside the Faraday effect element. Are positioned on the orbiting optical path.

In the configuration described above, the polarizer and the analyzer have Verdet constants sufficiently smaller than those of the Faraday effect element.

[Action]

As described above, the polarizer and the analyzer are arranged such that the light passage portion thereof is positioned so as to coincide with the orbiting optical path in the Faraday effect element when viewed from the running direction of the conductor. Integration can be performed, and detection can be performed in a state where there is no excess or deficiency in the round integration.

Therefore, the influence of the magnetic field of the other phase is remarkably reduced, and highly accurate and stable measurement can be performed.

〔Example〕

Hereinafter, an embodiment of an optical current transformer according to the present invention will be described with reference to FIGS. 1 (a) to 1 (e). In FIG. 1A, a Faraday effect element 2 made of, for example, lead glass is used.
A through hole φ is provided at the center thereof, and the conductor 1 is penetrated.

The Faraday effect element 2 has a rectangular shape when viewed from the running direction of the conductor 1. A rectangular notch 15 is formed at one corner thereof, and an analyzer 8 and a polarizer 7 are sequentially arranged on the side of the conductor 1 in the running direction.

The polarizer 7 is adapted to receive the parallelizer A _0, and after passing through the center O of the polarizer 7, the linearly polarized light A
Then, the light travels straight parallel to one side of the Faraday effect element 2, and reaches point a as shown in FIG. 1 (b). This point a is a portion where each of the front and back surfaces of the Faraday effect element 2 is inclined and cut, where it is totally reflected, and further, as shown in FIG. Go straight and reach point b. Also at this point b, the front and back surfaces of the Faraday effect element 2 are cut in a slanted manner, where they are totally reflected, and further, as shown in FIG. 1 (d), one side of the Faraday effect element 2 And go straight to the point c. Also at the point c, similarly, the front and back surfaces of the Faraday effect element 2 are cut by inclining the front and back surfaces.
As shown in FIG. 3D, the light beam goes straight to one side of the Faraday effect element 2 and reaches a position where the analyzer 8 is arranged. In this case, the light beam that circulates the Faraday effect element 2 with respect to the light beam incident on the polarizer 7 forms an optical path in a state of being shifted in the direction of the conductor 1. At the analyzer 8
Are arranged so as to overlap with the polarizer 7 when viewed from the running direction of the conductor 1. Then, the center O of the light passage portion of the analyzer 8 is positioned so as to coincide with the center O of the light passage portion of the polarizer 7 as viewed from the running direction of the conductor 1.

With this configuration, the polarizer 7 and the analyzer 8 are
When viewed from the running direction of the conductor 1, the light passing portion O is positioned so as to coincide with the orbiting optical path (0-abc-0) in the Faraday effect element 2. Therefore, the linearly polarized light part that depends on the magnetic field strength is all present in a closed loop, and it becomes a so-called complete circuit, the law of Ampere's circuit is established, and it is hardly affected by the other-phase magnetic field. become.

2 (a), 2 (b) and 2 (c) are configuration diagrams showing another embodiment of the optical current transformer according to the present invention. This figure has a schematic configuration similar to that of FIG. But,
When the polarizer 8 and the triangular prism 10 are fixed to each other, and the analyzer 7 and the triangular prism 11 are fixed to each other, each is viewed from the running direction of the conductor 1 and positioned so as to form a triangle. Each of the triangular prisms 10 and 11 is fixed to a surface of the Faraday effect element 2 where the corners are obliquely cut, thereby obtaining a configuration similar to that of FIG.

3 (a), (b), (c) and (d)
FIG. 6 is a configuration diagram showing another embodiment of the optical current transformer according to the present invention. The optical current transformer shown in FIG. 1 is configured such that the optical path makes one round of rotation, whereas the optical current transformer shown in FIG. It is intended for an optical current transformer that makes a total of two rounds by following a similar optical path.

In other words, the light becomes linearly polarized light after the parallel light A ₀ passing through the corner prism 12, a ', b', c ' and passes through the optical path L leading to the Q of the corner prism 12, the corner prism 12 Q, is totally reflected by R, c ", b", through the "optical path L leading to" a, parallel to (Fig. 3 and the parallel light a ₀ (b)
As shown in (2), when viewed from a direction perpendicular to the running direction of the conductor 1, a positional shift occurs.) The light is emitted out of the Faraday effect element 2.

In such an optical current transformer, O ₁ and O shown in FIG.
_As shown in FIG. 1, a polarizer and an analyzer are arranged at positions 2 so that they can be positioned at their respective central portions.

Even in this case, the polarizer and the analyzer can be positioned such that the light passage portions thereof are aligned with the orbiting optical path in the Faraday effect element, as viewed from the way the conductor runs.

According to the present embodiment, since the optical path of the reflection surface of the corner prism 12 is within the circular integration path, the influence of the other-phase magnetic field can be extremely reduced. Here, the optical paths between the reflecting surfaces Q and R overlap, but this is because the position of the incident light A is slightly
By sliding to the acute angle side of 12, the reflecting surfaces Q, R
It is possible to make the distance very short, and at the same time, by selecting the material of the corner prism 12 to be very small compared to the Verdet constant of the Faraday effect glass 2,
The same measurement accuracy as that of the embodiment shown in FIG. 1 can be obtained.

FIG. 4 is a block diagram showing another embodiment of the optical current transformer according to the present invention. This figure shows an optical current transformer that divides and divides the frequency twice as in FIG. 3. The difference from FIG. 3 is that the corner prism 12 that reflects back reflects the incident light and reflected light in the traveling direction of the conductor 1. From the point of view.

In this case, the light passing through the polarizer and the light passing through the analyzer are slightly shifted from the running direction of the conductor 1. However, the resulting shift is
Since it is small compared with the measurement deviation caused by the conventional configuration, the measurement accuracy is achieved by positioning the light passing portions of the polarizer and the analyzer at O ₁ and O ₂ in FIG. 4 (a).

〔The invention's effect〕

As is apparent from the above description, according to the optical current transformer according to the present invention, the influence of the magnetic field of the other phase is significantly reduced, and the measurement can be performed with high accuracy and stability.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an optical current transformer according to the present invention, FIGS. 2 to 4 are block diagrams showing another embodiment of an optical current transformer according to the present invention, and FIGS. FIG. 7 is a configuration diagram showing an example of a conventional optical current transformer. DESCRIPTION OF SYMBOLS 1 ... Conductor, 2 ... Faraday effect element, 3 ... Photocurrent sensor, 4 ... Light source, 5 ... Signal processing circuit, 6 ... Condensing lens, 7 ... Polarizer (P, B, S7) , 8 ... Analyzer (P, B,
S8), 9, 10, 11… right-angle prism, 12… corner prism, 13… sheath, PS… light output component, A ₀ … parallel light, A… linear polarization, L, L ′… ... optical path, H ... magnetic field, I
…… conductor current, φ …… through hole of conductor, ▲ ▼, ▲
▼: linearly polarized light part, ▲ ▼ ”, ▲ ▼”: space part, aa′a ″, bb′b ″, cc′c ″ ... total reflection surface, X ...
... Start point of the linearly polarized light portion of the incident light, Y...

Claims (2)

(57) [Claims] 1. A light is incident on a Faraday effect element installed around a conductor through a deflector, and after circulating around the conductor, light emitted from the Faraday effect element is extracted through an analyzer. In the optical current transformer for measuring the current in the conductor, the center of the light passage portion of the deflector coincides with the center of the light passage portion of the analyzer, as viewed from the running direction of the conductor, An optical current transformer, wherein the optical current transformer is arranged on a circuit light path in a Faraday effect element. 2. The optical current transformer according to claim 1, wherein the Verdet constant of the deflector and the analyzer is sufficiently smaller than the Welde constant of the Faraday effect element.