Optoelectric measuring device and method for measuring an electrical current

1. 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, said light source including 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;

a polarization-maintaining optical fiber connecting said polarization element and said Faraday sensor together to carry said polarized primary light signal;

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.

2. The measuring device according to claim 1 , 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.

3. The measuring device according to claim 2 , 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.

4. The measuring device according to claim 2 , wherein said Faraday sensor and said compensating Faraday sensor have an equivalent construction.

5. The measuring device according to claim 1 , wherein said detector is configured to detect a light intensity depending on a polarization state of the secondary light signal.

6. The measuring device according to claim 5 , wherein said detector has a polarization analyzer.

7. The measuring device according to claim 6 , 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.

8. The measuring device according to claim 1 , wherein said Faraday sensor has an optical fiber coil or a glass ring for guiding the primary light signal.

9. The measuring device according to claim 1 , 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.

10. The measuring device according to claim 9 ,

wherein said light source and said detector are disposed at ground potential.

11. The measuring device according to claim 10 ,

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.

12. The measuring device according to claim 1 , wherein at least a portion of said detector is disposed adjacent to a compensating Faraday sensor.

13. A method for measuring an electrical current, which comprises the steps of:

providing a measuring device according to clam 1 ;

feeding in a primary light signal generated by the light source, into the 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.

14. The method according to claim 13 , 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.

15. The method according to claim 14 , 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 electric conductor as a manipulated variable.