3-phase Faraday optical current sensor assembly

1. A method of measuring the current in a 3-phase cable comprising three individual section-shaped phase conductors insulated in relation to one another and encapsulated inside an insulator, the 3-phase cable defining a diameter, a longitudinal dimension along said 3-phase cable, and a radial dimension perpendicular to the longitudinal dimension, the method comprising:

providing a frame located outside of the insulator and spaced apart from the insulator;

providing a Faraday optical current sensor arrangement comprising three Faraday optical current sensors, each Faraday optical current sensor being fixed in a specific position on the frame outside of the insulator and spaced apart from the insulator;

providing a processing unit operable for calculating a current value from a magnetic field value input thereto;

measuring three magnetic field values by using each of the three Faraday optical current sensors; and

calculating a current value in each of the section-shaped phase conductors by using the processing unit with the three magnetic field values input thereto.

2. The method according to claim 1 , wherein each of the Faraday optical current sensors defines an individual light propagation direction, and wherein the step of providing a Faraday optical current sensor arrangement includes:

(a) positioning the Faraday optical current sensors annularly spaced by a specific angle around the 3-phase cable at an equal distance in relation to the longitudinal dimension and oriented such that the light propagation direction of each of the Faraday optical current sensors is oriented perpendicular to both the longitudinal dimension and the radial dimension; and

(b) fixing the Faraday optical current sensors in a measurement position in which the arithmetic sum of the current values is maximized.

3. The method according to claim 1 , wherein the frame comprises three plates, each plate having fixed thereto a Faraday optical current sensor.

4. The method according to claim 1 , wherein the frame comprises a circular plate mounted on the 3-phase cable parallel to the radial dimension, the circular plate defining:

a centrally located hole configured and located for accommodating the 3-phase cable, the centrally located hole having a diameter approximately equal to the diameter of the 3-phase cable; and

a detachable section defining an angle of approximately 120 degrees;

wherein the three Faraday optical current sensors are fixed on the circular plate at approximately equal distances from the 3-phase cable.

5. The method according to claim 1 , wherein the frame comprises:

first and second circular plates mounted on the 3-phase cable parallel to the radial dimension and separated by a specific distance along the longitudinal dimension, each circular plate defining:

a centrally located hole located and configured for accommodating the 3-phase cable, the centrally located hole having a diameter approximately equal to the diameter of the 3-phase cable; and

a detachable section defining an angle of approximately 120 degrees; and

three longitudinal plates each having a Faraday optical current sensor fixed thereto and extending between the first and second circular plates parallel to the longitudinal dimension, one of the longitudinal plates extending between the detachable sections of the first and second circular plates.

6. The method according to claim 1 , wherein the Faraday optical current sensors are fixed at equal distances from the 3-phase cable in relation to the radial dimension.

7. The method according to claim 1 , wherein the Faraday optical current sensors are fixed at equal distances from the 3-phase cable in relation to the longitudinal dimension.

8. The method according to claim 1 , wherein the 3-phase cable comprises a shield surrounding the section-shaped phase conductors.

9. The method according to claim 1 , wherein the 3-phase cable comprises a neutral conductor.

10. The method according to claim 1 , wherein the Faraday optical current sensors are positioned annularly spaced by an angle of approximately 120degrees around the 3-phase cable.

11. The method according to claim 10 , wherein the current in the 3-phase cable is calculated by the processing unit using the following formula:

I 1 =Gain( a )·φ( a )· I s +Gain( a )·φ(− a )· I i

I 2 =Gain( a )· b 2 ·φ( a )· I s +Gain( a )· b ·φ(− a )· I i

I 3 =Gain( a )· b ·φ( a )· I s +Gain( a )· b 2 ·φ(− a )· I i

with

b

=

1

2

+

j

·

3

2

,

φ(a)=cos(f(a))+j·sin(f(a)) and I s and I i considered as vectors and where I s represents a synchronous system current, I i represents an inverse system current, Gain(a) represents a reduction factor depending on an offset angle, and φ is a phase shift.

12. A system for measuring the currents in a 3-phase cable comprising 3 individual section-shaped phase conductors insulated in relation to one another and encapsulated inside an insulator, the 3-phase cable defining a diameter, a longitudinal dimension along the 3-phase cable and a radial dimension perpendicular to the longitudinal dimension, the system comprising:

a frame located outside of the insulator and spaced apart from the insulator;

a Faraday optical current sensor arrangement comprising three Faraday optical current sensors, each operable for measuring a magnetic field value, each Faraday optical current sensor being fixed in a specific position on the frame outside of the insulator and spaced apart from the insulator; and

a processing unit operable for calculating a current value in each of the section-shaped phase conductors in response to the input thereto of the magnetic field values from the three Faraday optical current sensors.

13. The system according to claim 12 , wherein each of the Faraday optical current sensors defines an individual light propagation direction, and wherein the Faraday optical current sensors are annularly spaced by a specific angle around the 3-phase cable at an equal distance in relation to the longitudinal dimension and oriented such that the light propagation direction of each of the Faraday optical current sensors is oriented perpendicular to both the longitudinal dimension and the radial dimension; and wherein the Faraday optical current sensors are fixed in a measurement position in which the arithmetic sum of the current values is maximized.

14. The system according to claim 12 , wherein the frame comprises three plates, each plate having fixed thereto a Faraday optical current sensor.

15. The system according to claim 12 , wherein the frame comprises a circular plate mounted on the 3-phase cable parallel to the radial dimension, the circular plate defining:

a centrally located hole configured and located for accommodating the 3-phase cable, the centrally located hole having a diameter approximately equal to the diameter of the 3-phase cable; and

a detachable section defining an angle of approximately 120 degrees;

wherein the three Faraday optical current sensors are fixed on the circular plate at approximately equal distances from the 3-phase cable.

16. The system according to claim 12 , wherein the frame comprises:

first and second circular plates mounted on the 3-phase cable parallel to the radial dimension and separated by a specific distance along the longitudinal dimension, each circular plate defining:

a centrally located hole located and configured for accommodating the 3-phase cable, the centrally located hole having a diameter approximately equal to the diameter of the 3-phase cable; and

a detachable section defining an angle of approximately 120degrees; and

three longitudinal plates each having a Faraday optical current sensor fixed thereto and extending between the first and second circular plates parallel to the longitudinal dimension, one of the longitudinal plates extending between the detachable sections of the first and second circular plates.

17. The system according to claim 12 , wherein the Faraday optical current sensors are fixed at equal distances from the 3-phase cable in relation to the radial dimension.

18. The system according to claim 12 , wherein the Faraday optical current sensors are fixed at equal distances from the 3-phase cable in relation to the longitudinal dimension.

19. The system according to claim 12 , wherein the 3-phase cable comprises a shield surrounding the section-shaped phase conductors.

20. The system according to claim 12 , wherein the 3-phase cable comprises a neutral conductor.

21. The system according to claim 12 , wherein the Faraday optical current sensors are positioned annularly spaced by an angle of approximately 120degrees around the 3-phase cable.