JPH07280849A - Optical current transformer - Google Patents

Abstract

PURPOSE:To provide an optical current transformer excellent in cost, performance, structure and environmental resistance. CONSTITUTION:A pair of single mode optical fibers 12, 13 are wound, with different number of turns, around a conductor 11 inserted into an objective line for detecting current in series therewith. Lights from light sources 14, 15 are passed through optical fibers 18, 19 to polarizers 20, 21 where the lights are subjected to linear polarization before being fed to optical fibers 12, 13. Optical signals having rotatory polarization varied by the current flowing through the conductor 11 is taken out as optical intensity signals through analyzers 22, 23. The optical intensity signals are taken in through optical fibers 24, 25 and converted into electric signals through optical detectors 28, 29 before the current values are determined at a current operating section 30. The current value detection signal is subjected to temperature compensation based on the temperature variation of both detection signals by taking advantage of the fact that variation in the duration of detection signals for a pair of optical fibers having different number of turns depends on the temperature variation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical current transformer utilizing the Faraday effect.

[0002]

2. Description of the Related Art Many optical current transformers utilize the interaction between a magnetic field and light and the magneto-optical effect, and among them, most utilize the Faraday effect.

The Faraday effect has been recognized in crystalline glass materials, and various forms have been considered depending on the application. Above all, when applied as an optical current transformer, particularly when detecting a three-phase current, a structure that avoids the influence of the currents of other phases as much as possible is desired.

FIG. 2 shows an example of a conventional circulating type optical current transformer. The conductor 1 through which the current to be measured flows is circularly constituted by _four Faraday cells 2 ₁ to 2 ₄ and prisms 3 ₁ to ₃ 3 as reflectors, and incident light from a light source is polarized by a lens 4 and a polarizer 5 to make a Faraday. The emitted light, which is introduced into the cell 2 ₁ and is influenced by the magnetic field generated by the current of the conductor 1 while circulating the Faraday cell and the prism, is led out by the analyzer 6 and the lens 7 at the end of the Faraday cell 2 ₄ and The emitted light whose intensity is modulated according to the current of 1 is obtained.

Faraday element materials include lead glass and BG.
Diamagnetic materials such as O (Bi ₁₂ GeO ₂₀ ) and BSO (Bi ₁₂ SiO ₂₀ ) are often used. This is for widening a wide magnetic field range, that is, a measured current range due to diamagnetism.

Of these, lead glass is amorphous, so that it is easy to manufacture with respect to cubic BGO and BSO, and the price per unit volume is low. However, in terms of performance, the Verdet constant, which indicates sensitivity, is a fraction of that of BGO and BSO, and is easily affected by noise in the small current region.

However, the temperature dependence of the Verdet constant is small,
There is an advantage that the characteristics are stable against changes in ambient temperature, and the material is selected in consideration of these matters.

[0008]

In the conventional revolving type optical current transformer, it is necessary to mold the sensor material in order to form a loop-shaped optical path around the conductor to be the current detection target.

Further, in order to circulate the light in a loop, it is necessary to use a molding process having a perfect reflecting surface, and if the reflecting surface is not suitable, the accuracy of the measured value will be deteriorated.

That is, since the Faraday effect used for detection detects the magnitude of the magnetic field (magnitude of the current) from the change in the polarization state of light, the change in the polarization state directly appears as the change in the measured value. At this time, if the reflection surface provided on the optical path changes the polarization state, it appears as a measurement value error.

Therefore, in the conventional revolving optical current transformer, many contrivances such as the processing method of the reflecting surface and the improvement of the sensor material are required to eliminate the influence on the polarization state on the reflecting surface, and the molding processing cost is high. And the sensor material becomes expensive.
For example, the sensor material is 10 compared to a wire wound type electromagnetic current transformer.
The price will exceed 0 times. Furthermore, handling (environment) of the sensor material becomes difficult.

In addition, when an optical current transformer is applied to gas-insulated substation equipment or the like, it is required that the performance does not deteriorate even if the environmental temperature changes greatly from -20 ° C to 90 ° C.
The structure and mechanism around the sensor, such as the support structure of the sensor body, also become expensive.

An object of the present invention is to provide an optical current transformer excellent in cost, performance, structure and environment resistance.

[0014]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a conductor inserted in series in a current detection target line and a pair of single windings wound around the conductor with different numbers of turns. Mode optical fiber, a polarization means for linearly polarizing monochromatic light from a light source and introducing the linearly polarized light into the pair of optical fibers, and a polarization detecting means for obtaining a light intensity signal according to the rotation amount of the polarization output of the pair of optical fibers, respectively. A current calculation unit that obtains a detection signal corresponding to the current value of the conductor from one of the light intensity signals obtained by the polarization detection unit and corrects the temperature of the detection signal from both of the light intensity signals. Characterize.

[0015]

[Function] A revolving optical current transformer is constituted by winding an optical fiber around a conductor.

Utilizing the Faraday effect of a single mode optical fiber, the strength of the magnetic field generated by the current of the conductor is extracted as a change in the rotation amount of the linearly polarized light propagating in the optical fiber, and this is detected by the polarization detecting means. It is taken out as a signal, and from this signal, the current calculation unit obtains it as a current detection value of the conductor.

By obtaining two detection values from a pair of optical fibers having different numbers of turns with respect to the conductor, the change in the length of the optical fiber due to the change in environmental temperature affects the rotation amount of the polarized light. Obtained from the amount of change in the detected value, temperature compensation of the detected current value is performed.

[0018]

1 is a block diagram showing an embodiment of the present invention. The conductor 11 is connected in series to a line that is a current detection target. Two optical fibers 12 and 13 are wound around the conductor 11. Fiber optics 12 and 13
Are made into a single mode optical fiber and have different numbers of turns. This conductor 11 and optical fibers 12 and 13
The coupling due to the magneto-optical effect may be a structure in which an optical fiber is wound around the conductor 11 wound in a coil shape.

Light linearly polarized by the polarization means is introduced into these optical fibers 12 and 13. This polarization means uses the coupler 1 for the monochromatic light from the light sources 14 and 15, respectively.
A polarizer 2 provided at the light introducing ends of the optical fibers 12 and 13 by taking in from 6 and 17 and guiding them to the mounting positions of the optical fibers 12 and 13 through the optical fibers 18 and 19.
Linearly polarized light is obtained with 0 and 21.

The optical fibers 18 and 19 are polarization maintaining optical fibers or fiber polarizers including a multimode optical fiber or a polarizer. As the polarizers 20 and 21, general PBSs, polarizing filters, polarizing prisms, polarizing plates, etc. can be used.

Therefore, linearly polarized light is introduced into the optical fibers 12 and 13, and the vibrating surface is rotated by the magnetic field generated by the current of the conductor 11 while propagating in the single mode optical fibers 12 and 13. This amount of rotation corresponds to the magnitude of the current in the conductor 11.

Next, polarization detecting means is provided at the light output ends of the optical fibers 12 and 13. This polarization detecting means is provided with analyzers 22 and 23 at the light output ends and takes out as a light intensity signal according to the rotation amount of the light polarized by the current of the conductor 11. .

Further, the optical outputs from the analyzers 22 and 23 are led to the couplers 26 and 27 at the ends through the optical fibers 24 and 25, respectively. Optical outputs from the couplers 26 and 27 are converted into electric signals by photodetectors 28 and 29, respectively.

The optical fibers 24 and 25 are composed of multimode optical fibers or the like, similarly to the structure of the optical fibers 18 and 19.

The light intensity of the light sources 14 and 15 is set so that the detection levels of the two detectors 28 and 29 become equal.

Therefore, the light passing through the optical fibers 12 and 13 is taken out by the photodetectors 28 and 29 as an electric signal of a light intensity signal corresponding to the rotation amount of the polarization.

The detection signals of both photodetectors 28 and 29 are fetched as a current calculation input to the current calculation section 30. The current calculation unit 30 calculates the current of the conductor 11 and the temperature correction calculation from both detection signals.

The current calculation in the current calculation unit 30 is performed from one detection signal of the photodetectors 28 and 29, and the calculation result is temperature-corrected from both detection signals.

This correction compensates for the optical paths 12 and 13 causing a change in optical path length due to a change in thermal expansion due to a change in temperature of the surrounding environment, and the change in optical path length appears as a change in polarization rotation amount.

That is, the optical fibers 12 and 13 made of the same material and having different lengths have different length changes even with the same temperature change, and the level change amount of the detection signal with respect to the temperature change is different. The difference between the amounts of change is used as calibration data for the current calculation unit 30.
By having it, the correction due to the change in environmental temperature is performed.

As described above, in the present embodiment, the current is detected by utilizing the Faraday effect of the optical fiber, and the temperature change is compensated by providing two detection systems having different lengths.

In the embodiment, the two light sources 1
4 and 15 and two detectors 28 and 29 are shown, but one light source and one detector may be used by utilizing a fiber demultiplexer, a beam splitter, a half mirror, or the like.

[0033]

As described above, according to the present invention, a circular optical current transformer is constructed by winding an optical fiber around a conductor, and two detection values are obtained from a pair of optical fibers having different numbers of turns with respect to the conductor. By obtaining the compensation, the compensation due to the change of the environmental temperature is achieved, and the following effects are obtained.

(1) Since it is a revolving type optical current transformer that uses the Faraday effect of an optical fiber, it is smaller in size and lighter in structure while having the features of a revolving type compared to conventional revolving type optical current transformers. Can be achieved.

(2) In order to obtain the magneto-optical effect between the linearly polarized light and the current / magnetic field, a revolving type optical current transformer can be constructed without the need for a conventional reflection prism, etc., which simplifies production and maintenance and reduces the cost. Cost and reliability can be improved.

(3) Since temperature compensation of the current detection signal is obtained using a pair of optical fibers having different numbers of turns with respect to the conductor, environmental resistance can be improved and high accuracy can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 shows an example of a conventional circulating optical current transformer.

[Explanation of symbols]

 11 ... Conductor 12, 13 ... Optical fiber 14, 15 ... Light source 16, 17, 26, 27 ... Coupler 18, 19, 24, 25 ... Optical fiber 20, 21 ... Polarizer 22, 23 ... Analyzer 28, 29 ... Photodetector 30 ... Current calculation unit

Claims (1)

[Claims] 1. A conductor inserted in series with a current detection target line, a pair of single-mode optical fibers wound around the conductor with different numbers of turns, and linearly polarized monochromatic light from a light source, Polarizing means respectively introduced into the pair of optical fibers, polarization detecting means for respectively obtaining a light intensity signal corresponding to the rotation amount of the polarized output of the pair of optical fibers, and one of the conductors from one of the light intensity signals obtained for the polarization detecting means. An optical current transformer, comprising: a current calculation unit that obtains a detection signal corresponding to a current value, and temperature-corrects the detection signal from both light intensity signals.