Patent ID: 12210042

DETAILED DESCRIPTION OF INVENTION

Mutually corresponding parts are provided with the same reference signs in the figures.

FIG.1(FIG.1) shows a block diagram of one exemplary embodiment of a magneto-optic current transformer1for detecting a current intensity of an electric current in a current conductor2. The current transformer1comprises a light supply device3, two light guide units5,6and an analysis device7.

The light supply device3is configured to feed light9,10to the light guide units5on the input side. The light supply device3comprises for each light guide unit5,6a light source11,12, a collimator unit13,14and an optical waveguide15,16on the input side (relative to the light guide unit5,6). Each light source11,12is designed in each case as a light emitting diode, for example. Each collimator unit13,14focuses light9,10generated by a light source11,12and feeds the light9,10into an optical waveguide15,16. Each optical waveguide15,16forwards the light9,10fed to it to a light guide unit5,6.

Each light guide unit5,6comprises a linear input polarizer17,18, a linear output polarizer19,20and a light guide21,22arranged between the input polarizer17,18and the output polarizer19,20in the region of the current conductor2, said light guide exhibiting the Faraday effect and being configured to feed light transmitted by the input polarizer17,18to the output polarizer19,20.

The analysis device7is configured to detect for each light guide unit5,6a light intensity of light9,10output by the light guide unit5,6on the output side, and to determine the current intensity of the electric current through the current conductor2from the detected light intensities. For this purpose, the analysis device7has for each light guide21,22an optical waveguide23,24on the output side (relative to the light guide unit5,6) and a photodetector25,26. The optical waveguide23,24feeds light9,10output by the light guide21,22to the photodetector25,26. The photodetector25,26is configured to detect the light intensity of the light9,10fed to it. Each photodetector25,26is designed as a photodiode, for example. Furthermore, the analysis device7comprises an evaluation unit27, which evaluates the light intensities detected by the photodetectors25,26and ascertains therefrom the current intensity of the electric current through the current conductor2.

FIG.2(FIG.2) shows a perspective basic illustration of the light guides21,22of one exemplary embodiment of a magneto-optic current transformer1. The light guides21,22are embodied identically, run in each case in a ring-shaped manner along a quadrilateral around the current conductor2and are fabricated from a glass, for example from optic flint glass. In a departure fromFIG.2, the light guides21,22in the real embodiment have outer surfaces which face away from the current conductor2and which are angled by 45 degrees in the corner regions of the respective quadrilateral in order to deflect the light9,10there by 90 degrees by way of total internal reflection. However, the exact embodiment of the light guides21,22is not relevant to the invention and is therefore not illustrated here.

The polarization axis of the output polarizer19,20of each light guide unit5,6is rotated by a polarization angle relative to the polarization axis of the input polarizer17,18of the light guide unit5,6, wherein the polarization angles of the two light guide units5,6differ from one another.

By means of the input polarizer17,18of a light guide unit5,6, light9,10fed to the light guide unit5,6is linearly polarized parallel to the polarization axis of the input polarizer17,18. If a current flows in the current conductor2, the polarization direction of the light9,10is rotated while passing through the light guide21,22of the light guide unit5,6on account of the Faraday effect. The output polarizer19,20transmits a portion of the light9,10that is parallel to the polarization axis of the output polarizer19,20.

The light intensity of the light9,10output by a light guide unit5,6therefore depends on an angle of rotation φ by which the polarization direction of the light9,10is rotated when passing through the light guide21,22of the light guide unit5,6. Since the light guide units5,6are designed identically, the angle of rotation φ is identical for both light guide units5,6. Since the polarization angles of the two light guide units5,6differ from one another, however, the proportions of the light transmitted by the output polarizers19,20of the two light guide units5,6differ from one another, however (except for specific angles of rotation φ). Therefore, the normalized light intensities output by the light guide units5,6also differ from one another, wherein the normalized light intensity output by a light guide unit5,6is defined as the ratio I/Imaxof the light intensity I of the light9,10output by the light guide unit5,6to a maximum light intensity Imaxattained if the polarization direction of the light9,10after passing through the light guide21,22of the light guide unit5,6is parallel to the polarization axis of the output polarizer19,20of the light guide unit5,6.

FIG.3(FIG.3) shows characteristic curves I1, I2for the normalized light intensities which are output by the light guide units5,6in the case where a first light guide unit5has a polarization axis of 45 degrees and the second light guide unit6has a polarization axis of 90 degrees. In this case, I1denotes the characteristic curve of the first light guide unit5and I2denotes the characteristic curve of the second light guide unit6. Each characteristic curve I1, I2indicates the normalized light intensity as a function of the angle of rotation φ, which indicates the extent to which the polarization direction of the light9,10is rotated when passing through the light guide21,22of the respective light guide unit5,6.

Since the first light guide unit5has a polarization angle of 45 degrees in the example considered here, the characteristic curve I1has a minimum of normalized light intensity zero at −45 degrees (modulo 180 degrees), since at φ=−45° the polarization direction of the light9at the output polarizer19is orthogonal to the polarization axis of the output polarizer19, and a maximum of normalized light intensity one at 45 degrees (modulo 180 degrees), since at φ=45° the polarization direction of the light9at the output polarizer19is parallel to the polarization axis of the output polarizer19. Accordingly, the characteristic curve I2has a minimum of normalized light intensity zero at φ=0° (modulo 180 degrees) and a maximum of normalized light intensity one at φ=90° (modulo 180 degrees) since the second light guide unit6has a polarization axis of 90 degrees in the example considered here.

FromFIG.3, a number of advantages of the use of two light guide units5,6having different polarization axes can be elucidated by way of example. For example,FIG.3shows that the characteristic curve I1yields identical values for the angles of rotation φ=30° and φ=60° (or more generally for φ=45°−α and φ=45°+α), such that these values are not distinguishable by way of the first light guide unit5alone. The same correspondingly applies for example to the angles of rotation φ=−60° and φ=−30° (or more generally for φ=−45°−α and φ=−45°+α). In other words, if only the first light guide unit5were used, the measurement range would have to be restricted for example to the angle range [−45°, 45°] or to the currents associated therewith in the current conductor2in order that a current intensity of a current in the current conductor2is unambiguously assigned to a normalized light intensity output by the first light guide unit5. The additional use of the second light guide unit6makes it possible to extend this measurement range, however, since the characteristic curve I2of the second light guide unit6has different values for example for the angles of rotation φ=30° and φ=60° and also φ=−60° and φ=−30° and thus makes it possible to resolve the ambiguity of the characteristic curve I1at these angles of rotation.

Furthermore, the use of two light guide units5,6having different polarization angles can be utilized for identifying defects of the current transformer1. By way of example, in the case where only the first light guide unit5is used, it is not possible to distinguish between the case of an angle of rotation of φ=−45° (or an angle of rotation close to φ=−45°) and the case where a light feed to the first light guide unit5fails or is interrupted (for example owing to a defect of the optical waveguide15, of the optical waveguide23and/or a failure of the light source11). Additionally taking account of the second light guide unit6makes it possible to draw such a distinction, however, since the characteristic curve I2of the second light guide unit6at φ=−45° assumes a value that is distinctly different from zero.

Furthermore, there is no value of the angle of rotation φ for which both characteristic curves I1, I2assume a vanishing normalized light intensity. If no light intensity is detected for both light guide units5,6, a defect of the current transformer1can therefore be deduced.

Furthermore, the two characteristic curves I1, I2define a difference characteristic curve ΔI(φ)=I1(φ)−I2(φ) for all values of the angle of rotation φ. A great deviation from the difference characteristic curves ΔI(φ) by a difference between the light intensities detected for the two light guide units5,6can thus likewise indicate a defect of the current transformer1. In particular, a tolerance range R for said difference can be predefined as a range around the difference characteristic curve ΔI(φ) and a defect of the current transformer1can be deduced if the difference between the normalized light intensities detected for the two light guide units5,6lies outside the tolerance range R. In this case, the width of the tolerance range R around the difference characteristic curve ΔI(φ) takes into account for example the measurement accuracies of the detection of the light intensities.

Although the invention has been more specifically illustrated and described in detail by way of preferred exemplary embodiments, nevertheless the invention is not restricted by the examples disclosed and other variations can be derived therefrom by a person skilled in the art, without departing from the scope of protection of the invention.