JPS5935156A - Optical current transformer - Google Patents

Abstract

PURPOSE:To enable measurement in a wide range from a low magnetic field to a high magnetic field, by arranging a plurality of a magnetical optical rotatory bodies comprising different materials in parallel to make it possible to use one magnetical optical rotatory body corresponding to a measuring range. CONSTITUTION:A magnetical optical rotatory body 5 having a light path provided to the interior thereof and formed of lead glass and a magnetical optical rotatory body 13 formed of quartz glass are arranged in parallel so as to cross a current flowing through a primary conductor 12. Linear polarized light is projected to the optical rotatory body 5 from a light source 1 through a polarizer 4. This linear polarized light is emitted from an emitting surface after going round the primary conductor 12 to be separated into its spectral components by an analyser 6 and received by a light receiver 11 to be converted to an electric signal which is, in turn, converted to a rotary angle signal Va by an operator 14 to be inputted to an OR circuit 15. Similar operation is performed with respect to the side of the optical rotatory body 13. In this case, a max. value of the rotary angle signals Va, Vb is outputted from the circuit 15. The output from the circuit 15 is shown by the solid line of the drawing and the measurement of a current from a low magnetic field to a high magnetic field is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical current transformer, and more particularly to an optical current transformer suitable for measuring a current flowing through a high voltage conductor.

As is well known, when linearly polarized light passes through a transparent material such as lead glass placed in a magnetic field caused by an electric current, the plane of polarization of the linearly polarized light rotates by an angle θ expressed by the following equation.

θ=VHL ・・・・・・・・・・・・・・・・・・
(1) where ■ is Weerde's constant, H is the strength of the magnetic field in the direction in which the light travels, and L is the optical path length of the light passing through the transparent material.

This phenomenon is called the Faraday effect, and a substance that exhibits the Faraday effect is called a magnetic optical rotator.By detecting the angle θ in equation (1) above using a well-known method and detecting the magnetic field strength H, the magnetic optical rotator can be Optical current transformers that measure the current flowing nearby are generally known (8.3aito, et al. 4: The L
a5er Current 'transformer
forBHy power Transmission
n Lines+IEEE Journal of Qu
antum Electronics VOI, QE-
2, No. 8, Aug. 1966).

An example of this optical current transformer is shown in FIG. light emitting diode,
A part of the light emitted by a light source 1 composed of one of a laser diode, a laser, etc. propagates through an optical fiber 2, is focused by a condensing lens 3, and then passes through a polymer film, a vapor-deposited film, and a polarizing prism. The light is made into linearly polarized light by a well-known polarizer 4 such as Etc., and then enters a magnetic optical rotator 5 . Magnetic rotator 5
is composed of a substantially rectangular flat plate with a through hole in the center through which the primary conductor 12 is passed, and the incident light a incident on the magnetic optical rotator 5 is fully focused twice at each corner. The light is reflected and goes around the one-groove body 12 and exits, and is transmitted to the light receiver 1 via the analyzer 6, the condensing lens 7.8 and the optical fiber 9.10.
The light is received at 1. According to this magnetic optical rotator 5, since the incident light a is totally reflected twice at each corner (six times in total), linearly polarized light changes to elliptically polarized light, and the amount of angular change θ decreases, resulting in output sensitivity. (Saito et al. 3; Basic research on laser-based power current and voltage measurement devices; University of Tokyo Production Technology Research Report. VOl, 28, No. 5, M
arclt 1980).

Here, the rotation of the plane of polarization of linearly polarized light due to the Faraday effect is proportional to the strength of the magnetic field parallel to the optical path and the length of the optical path, and the linearly polarized light incident on the magnetic optical rotator 5 goes around the single groove member 12. For emission, the rotation angle θ due to the Faraday effect is expressed by the following equation (2), and is proportional only to the current ■ of the primary conductor interlinked with the optical path.

θ=VVH(lt=VI・・・・・・・・・・・・・
...(2) However, t is the optical path length.

Note that the influence of the current flowing in other conductors near the one-groove body 12 can be ignored because it becomes zero when integrated along the optical path.

As mentioned above, an optical current transformer using a magnetic optical rotator has the very excellent feature of being able to measure the current flowing in a specific conductor without being affected by the current flowing in other conductors. As the magnetic optical rotator, lead glass, heavy flint glass, magnetic glass, quartz glass, etc. are used.

However, the amount of rotation due to the Faraday effect differs depending on the material, and when a magnetic optical rotator made of a single material is used as an optical current transformer, there is a limit to the measurement range. For example, the rotation angle due to the Faraday effect of lead glass is 0.12 min/AT for light with a wavelength of 633 nm, but for silica glass of the same shape and size, it is 0.012 min/AT.
It becomes 1/10 of Totori lead glass.

That is, in the case of lead glass, the rotation angle is large, so it is suitable for measurements in low magnetic fields, but in high magnetic fields, the rotation angle becomes saturated, making it impossible to measure positive magnetism. On the other hand, in the case of quartz glass, the rotation angle is small, so it is suitable for measuring high magnetic fields, but the sensitivity is too low for measuring low magnetic fields, resulting in a decrease in accuracy.

As described above, the conventional optical modulator using a magnetic optical rotator has a problem in that it cannot continuously measure a wide range.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to provide an optical current transformer that makes it possible to measure current over a wide range with high precision.

The configuration of the present invention is such that, in a conventional optical current transformer using a magnetic optical rotator, a plurality of magnetic optical rotators made of different materials are arranged in parallel. As a result, 1
A wide range of measurements from low to high magnetic fields is possible.

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 2 shows an embodiment of the present invention. Note that in FIG. 2, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and explanations thereof will be omitted.

As shown in the figure, the first groove body 12 is made of lead glass and has an optical path therein so as to interlink with the current flowing through the groove body 12.
A second magnetic optical rotator 5 and a second magnetic optical rotator 13 made of silica glass and provided with an internal optical path so as to be interlinked with the current flowing through the first grooved body 12 are arranged in parallel. .

The first magnetic optical rotator 5 includes an optical fiber 2 from the light source 1,
Linearly polarized light is incident through a condenser lens 3 and a polarizer 4 . The incident linearly polarized light is totally reflected twice at each corner of the flat first magnetic optical rotation body 5, goes around the one-groove body 12, and then exits from the exit surface and passes through the Rochon prism and the Wollaston prism. The light is separated by an analyzer 6 composed of a polarizing beam splitter, etc., and is received by a light receiver 11 such as a photodiode via a condenser lens 7.8 and an optical fiber 9.10, and converted into an electric signal.

This electrical signal is converted into a rotation angle signal V by the calculator 14.

and is input to the OR circuit 15.

As described above, the second magnetic optical rotator 13 includes a light source 1′.
Linearly polarized light is incident from the optical fiber 2', the condensing lens 3, and the polarizer 4'. The incident linearly polarized light is
Similarly to the above, it is totally reflected twice at each corner of the second magnetic optical rotator 13, goes around the one-groove member 12, and then exits from the exit surface, is deflected by the analyzer 6', and then passes through the condenser lens. 7', 8' and optical fibers 9', 10"e, the light is received by the light receiver 11' and converted into an electrical signal. This electrical signal is converted into a rotation angle signal vb by the calculator 14', and the OR The signal is input to the circuit 15.

Then, the maximum value of the rotation angle signals v, , v, is the OR circuit 1
Output from 5. The signal output from the OR circuit 15 is as shown by the solid line in FIG. 3, and current measurement is possible from a low magnetic field to a high magnetic field.

As explained above, according to the present invention, the excellent effect of expanding the current measurement range without being affected by other currents and enabling highly accurate measurement can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a conventional optical current transformer, FIG. 2 is a schematic diagram showing an embodiment of the present invention, and FIG. 3 is a diagram showing the output of the optical current transformer. 1... Light source, 4... Polarizer, 6... Analyzer, 5.
13... emotion (ward output ≠ Z mouth e-j; JV

Claims (1)

[Claims] 1. A light source, a magnetic optical rotator having an optical path formed therein so as to interlink with the current to be measured, a polarizer disposed between the light source and the incident surface of the magnetic optical rotator, and the magnetic and a detector disposed on the exit surface side of the magnetic optical rotator, and detects the magnitude of the current based on the rotation angle of the polarization plane of the linearly polarized light that has passed through the magnetic optical rotator, An optical current transformer characterized in that a plurality of magnetic optical rotators made of different materials are arranged in parallel.