Optoelectric Measuring Device And Method For Measuring An Electrical Current

Abstract

A measuring device measures an electrical current and contains a light source for generating a polarized primary light signal for feeding into a Faraday sensor unit, and a detector for detecting a secondary light signal provided by the Faraday sensor unit and polarization-altered in relation to the primary light signal. An optical-electrical compensation element, by which the polarization alteration of the secondary light signal can be compensated via an opposite polarization alteration, and a measurement signal, according to the opposite polarization alteration, for the electrical current can be deduced. A method for measuring an electrical current by use of the measuring device is further disclosed.

Claims

1-15. (canceled)

16. A measuring device for measuring an electrical current, the measuring device comprising: a Faraday sensor; a light source for generating a polarized primary light signal for feeding into said Faraday sensor device; a detector for detecting a secondary light signal provided by said Faraday sensor device and altered in polarization in relation to the polarized primary light signal; and a compensation element, by which a change in the polarization of the secondary light signal can be compensated for by an opposite change in the polarization, and a measurement signal that depends on the opposite change in the polarization can be derived for the electrical current.

17. The measuring device according to claim 16, wherein said compensation element has a compensating Faraday sensor and a compensation electrical conductor disposed close to said compensating Faraday sensor, wherein the secondary light signal passes through said compensating Faraday sensor, and a compensation current in said compensation electrical conductor can be adjusted in such a way that a change in the polarization of the secondary light signal can be compensated, wherein the measurement signal can be derived from the compensation current.

18. The measuring device according to claim 17, wherein said compensation element has a control device that is configured for a zero-regulation of the change of polarization of the secondary light signal or of a controlled variable derived from it, making use of the compensation current as a manipulated variable.

19. The measuring device according to claim 17, wherein said Faraday sensor and said compensating Faraday sensor have an equivalent construction.

20. The measuring device according to claim 16, wherein said detector is configured to detect a light intensity depending on a polarization state of the secondary light signal.

21. The measuring device according to claim 20, wherein said detector has a polarization analyzer.

22. The measuring device according to claim 21, wherein said polarization analyzer is adjusted such that the secondary light signal without a change of polarization results in a zero-signal at an output of said detector.

23. The measuring device according to claim 16, wherein said Faraday sensor has an optical fiber coil or a glass ring for guiding the primary light signal.

24. The measuring device according to claim 16, wherein said Faraday sensor is disposed close to a high-voltage electrical conductor, so that the measurement signal for the electrical current in the high-voltage electrical conductor can be derived.

25. The measuring device according to claim 24, wherein said light source and said detector are disposed close to a ground potential; wherein said light source has an optical fiber, a light generation element and, separate from said light generation element, a polarization element, said light generation element and said polarization element are connected together by means of said optical fiber; and further comprising a polarization-maintaining optical fiber to carry the primary light signal which connects said polarization element and said Faraday sensor together.

26. The measuring device according to claim 25, wherein said detector contains a further optical fiber, a polarization analyzer and, separate from said polarization analyzer, an intensity sensor, said polarization analyzer and said intensity sensor are connected together by said further optical fiber; and further comprising another polarization-maintaining optical fiber to carry the secondary light signal, which connects said Faraday sensor and said polarization analyzer together.

27. The measuring device according to claim 16, wherein said detector is disposed physically close to said compensating Faraday sensor.

28. A method for measuring an electrical current, which comprises the steps of: feeding in a primary light signal generated by means of a light source, into a Faraday sensor and the Faraday sensor providing a secondary light signal with a polarization that has been changed in relation to the primary light signal; compensating for, via a compensation element, a change in the polarization of the secondary light signal by an opposite change in the polarization; and deriving a measurement signal that depends on the opposite change in the polarization for the electrical current.

29. The method according to claim 28, which further comprises performing the compensating step for compensation of the change of polarization of the secondary light signal by means of a zero-regulation of the change of polarization or by means of a zero-regulation of a controlled variable derived from that.

30. The method according to claim 29, wherein the secondary light signal passes through a compensating Faraday sensor which is disposed physically close to a compensation electric conductor, and the zero-regulation is performed with a compensation current through the compensation electrical conductor as a manipulated variable.

Description

[0034] The invention is further explained below with reference to FIGS. 1 to 3.

[0035] FIG. 1 shows a schematic structure of an exemplary embodiment of a measuring device according to the invention;

[0036] FIG. 2 shows a schematic representation of a further exemplary embodiment of the measuring device according to the invention;

[0037] FIG. 3 shows a schematic representation of a further alternative exemplary embodiment of the device according to the invention.

[0038] A sketch of a measuring device 1 is accordingly illustrated in the figure. The measuring device 1 comprises a Faraday sensor device 2 which is arranged close to a high-voltage electrical conductor 3. The Faraday sensor device 2 comprises a plurality of optical fiber windings 21 which are wound around the high-voltage electrical conductor 3. In the variant illustrated here, the electrical conductor 3 is part of a high-voltage installation (not illustrated).

[0039] The high-voltage electrical conductor 3 is thus at a high-voltage potential. An insulation element 4 is provided for a potential insulation between the high-voltage potential and the ground potential, extending between the high-voltage electrical conductor 3 and the ground, and is illustrated here as being formed as a hollow insulator. The insulation element 4 further comprises an insulator foot 41, on which the insulation element 4 is placed.

[0040] The measuring device 1 further comprises a light source 5. The light source 5 comprises a light generation element 51 and a polarization element 52. The polarization element 52 is arranged in the insulating foot 41. The light generation element 51 is arranged in a building 7. The building 7 is set up to house parts of the measuring device 1 as well as further parts of the high-voltage installation. In the figure, a line 18 is used to suggest that the distance between the building 7 and the insulation element 4 can be up to several thousand meters. The light generation element 51 and the polarization element 52 are connected together by means of an optical fiber 53.

[0041] The detector comprises a polarization analyzer 61, an intensity sensor 62 and an optical fiber 63, where the optical fiber 63 connects the polarization analyzer 61 to the intensity sensor 62. The polarization analyzer 61 is arranged, in the form illustrated, in the insulator foot 41. The intensity sensor 62 is arranged in the building 7, also at ground potential.

[0042] The measuring device 1 further comprises a compensating Faraday sensor device 8 that is integrated into an optical fiber 19 extending between the polarization analyzer 61 and the Faraday sensor device 2. In the exemplary embodiment of the invention illustrated in the figure, the compensating Faraday sensor device 8 is constructed as a fiber coil, where the fiber windings of the fiber coil are wound around a compensation electrical conductor 9. In the exemplary embodiment illustrated, the compensation electrical conductor 9 comprises a plurality of windings of an electrical conductor.

[0043] The measuring device 1 furthermore comprises a control device 10 which, in the variant illustrated here, is arranged in the building 7. The control device 10 is illustrated in a simplified manner in the figure. The control device 10 accordingly comprises a measurement resistor 11, a feedback loop 12 and a voltage source 13. The control device 10 is connected by means of electrically conductive connections 14 and 15 to the compensation electrical conductor 9, so that a suitable circuit is formed.

[0044] In the exemplary embodiment illustrated, the compensating Faraday sensor device 8, the compensation electrical conductor 9 and the control device 10 form elements of a compensation element.

[0045] The manner in which the measuring device 1 functions will be considered more closely below. A light signal is generated by means of the light generation element 51. This light signal does not yet have any defined polarization. The light signal is passed through the optical fiber 53 to the polarization element 52. The light signal is set into a well-defined polarization state by means of the polarization element 52. The polarized primary light signal is accordingly provided at the output of the polarization element 52. The primary light signal is passed to the Faraday sensor device 2 by means of a polarization-maintaining optical fiber 16. The primary light signal circulates around the high-voltage electrical conductor 3. The primary light signal has linear polarization in the exemplary embodiment of the measuring device 1 illustrated in the figure. This means that the primary light signal exhibits a well-defined polarization angle with respect to a predefined zero angle, e.g. zero degrees. As a result of the Faraday effect, this polarization angle changes in the magnetic field of the high-voltage electrical conductor 3. This means that a secondary light signal with a changed polarization is provided at the output of the Faraday sensor device. The secondary light signal passes through the optical fiber 19, and is fed into the compensating Faraday sensor device 8. By means of the current flowing through the compensation electrical conductor 9 a magnetic field can be generated here, which creates an opposite change in the polarization of the secondary light signal in the compensating Faraday sensor device.

[0046] For the purposes of explanation, it will be assumed below that in the presence of a given current ih through the high-voltage electrical conductor 3, the secondary light signal exhibits a change of polarization that corresponds to a rotation of the plane of polarization through an angle ah. The opposite polarization in the compensating Faraday sensor device 8 creates, for example, in the presence of a given value ik of the compensation current, a rotation of the angle of polarization through the additional angle ak, which can also adopt negative values. At the output of the compensating Faraday sensor device, the secondary light signal thus in total exhibits a rotation of the plane of polarization through the angle ah+ak. An intensity signal that depends on the angle ah+ak is generated in the polarization analyzer 61, and is passed to the intensity sensor 62. The polarization analyzer 61 is set up in such a way that it outputs a zero intensity signal for the angle ah+ak=0°. If the intensity signal is not equal to zero, then a positive or negative amplification of the compensation current is created through the feedback loop 12. It is possible to determine whether an over-compensation or an under-compensation is present, i.e. whether a positive or negative amplification should be applied, for example by means of a suitable additional measurement, a suitably selected evaluation, or through an overlaid high-frequency signal outside the measuring range. The value of the angle ak can in turn be affected in this way. If the compensation current ik is finally adjusted such that it causes rotation of the plane of polarization through an angle ak such that ah+ak=0, then the complete compensation of the change of polarization of the secondary light signal through opposite polarization has been reached. The voltage Umax measured at the measurement resistor 11 at this compensation current carries the information about the electrical current ih in the high-voltage electrical conductor 3.

[0047] A further exemplary embodiment of the measuring device 100 according to the invention is sketched in FIG. 2. Identical parts have been given the same reference signs in the FIGS. 1 and 2. The general manner in which the measuring device 100 functions corresponds to that of measuring device 1. For reasons of clarity, only the differences between the exemplary embodiments of the FIGS. 1 and 2 will be considered in more detail below.

[0048] The measuring device 100 of FIG. 2 differs from the measuring device 1 of FIG. 1 in that the polarization element 52 and the polarization analyzer 61 in FIG. 1 are replaced in FIG. 2 by a phase modulator 54. The phase modulator 54 has two inputs and two outputs. The phase inputs and outputs of the phase modulator 54 are arranged such that the primary light signal and the secondary light signal pass through the phase modulator 54.

[0049] An alternative exemplary embodiment of a measuring device 200 according to the invention is sketched in FIG. 3. Identical or similar parts of the measuring devices 100 and 200, respectively, have been given the same reference signs in the FIGS. 1 and 3. Only the differences between the measuring devices 100 and 200 of FIGS. 2 and 3 are considered in more detail below.

[0050] In the exemplary embodiment of FIG. 3, the measuring device 200 also has a phase modulator 54. The phase modulator 54 of measuring device 200 has two inputs and one output. The polarization-maintaining optical fibers 16 and 19 of the measuring device 100 of FIG. 2 thus coincide in the measuring device 200 of FIG. 3. Both the primary light signal and the secondary light signal thus pass along the polarization-maintaining optical fiber 16. The primary light signal and the secondary light signal are overlaid in the optical fiber 16. The measuring device 200 further comprises a mirror 20 that is arranged at the Faraday sensor device. The primary light signal reflects at the mirror 20, and thus reverses its direction of propagation.

[0051] List of Reference Signs

[0052] 1, 100, 200 Measuring device

[0053] 2 Faraday sensor device

[0054] 21 Fiber winding

[0055] 3 High-voltage electrical conductor

[0056] 4 Insulation element

[0057] 41 Insulator foot

[0058] 5 Light source

[0059] 51 Light generation element

[0060] 52 Polarization element

[0061] 53, 63 Optical fiber

[0062] 54 Phase modulator

[0063] 6 Detector

[0064] 61 Polarization analyzer

[0065] 62 Intensity sensor

[0066] 7 Building

[0067] 8 Compensating Faraday sensor device

[0068] 9 Compensation electrical conductor

[0069] 10 Control device

[0070] 11 Measurement resistor

[0071] 12 Feedback loop

[0072] 13 Voltage source

[0073] 14, 15 Optical fiber

[0074] 16, 19 Polarization-maintaining optical fiber

[0075] 20 Mirror