Electric cable with bending sensor and monitoring system and method for detecting bending in at least one electric cable

1. A deformation monitoring method for measuring at least the bending strain of an electric cable having a geometric axis, comprising:

providing the cable with at least one peripheral mechanically non-symmetric strength member having higher resistance to tensile loads than to compressive loads, at least two longitudinal structural elements, and an optical fiber sensor located in a geometrical axis region of the cable and comprising an optical fiber, wherein the sensor is embedded in a strain-transferring filler mechanically coupling the sensor with at least one of the at least two longitudinal structural elements; and

detecting compressive strain in the optical fiber sensor;

wherein an entire outer perimeter of the sensor is in contact with the strain-transferring filler.

2. The method according to claim 1 , wherein detecting compressive strain comprises:

injecting a first optical signal into the optical fiber;

detecting Brillouin scattered light emitted from the optical fiber; and

analyzing spectral changes in the scattered light so as to measure at least the bending strain of the cable.

3. The method according to claim 1 , wherein the cable is substantially round and comprises the optical fiber sensor within a radial distance from the geometrical axis of not more than 20% of cable radius.

4. The method according to claim 3 , wherein the optical fiber sensor is within a radial distance from the geometrical axis of not more than 10% of the cable radius.

5. The method according to claim 1 , wherein the cable is substantially round and comprises the at least one peripheral mechanically non-symmetric strength member disposed along at a radial distance from the geometrical axis of at least 50% of the cable radius.

6. The method according to claim 1 , wherein the cable is flat and comprises the optical fiber sensor within a radial distance from the geometrical axis of not more than 10%.

7. The method according to claim 1 , wherein the cable is flat and comprises the at least one peripheral mechanically non-symmetric strength member disposed at a distance from the geometrical axis of at least 50% of cable thickness.

8. The method according to claim 1 , wherein the cable is substantially round and the peripheral mechanically non-symmetric strength member includes a cable anti-torsional braid.

9. The method according to claim 1 , wherein the cable is flat and comprises at least two parallel electric conductors and the peripheral mechanically non-symmetric strength member includes a pull strength element provided in interstices between conductors.

10. The method according to claim 1 , wherein the at least one of the at least two longitudinal structural elements comprises an electrical conducting element.

11. The method according to claim 1 , wherein the two longitudinal structural elements are in contact with a polymeric filler.

12. The method according to claim 1 , wherein the strain-transferring filler comprises an elastomer having an elastic modulus from 0.01 to 0.7 GPa.

13. The method according to claim 1 , wherein the strain-transferring filler comprises a thermosetting elastomer.

14. The method according to claim 1 , wherein the strain-transferring filler is selected from the group consisting of a polyester having an elastic modulus from 1 to 5 GPa, a polyamide having an elastic modulus from 2 to 4 GPa, a polyvinyl chloride having an elastic modulus 0.003 to 0.01 GPa, a low-density polyethylene having an elastic modulus from 0.1 to 0.3 GPa, and a high-density polyethylene having an elastic modulus of from 0.4 to 1.2 GPa.

15. The method according to claim 1 , wherein the optical fiber of the optical fiber sensor is coated with a coating system and tight-buffered with a buffer layer surrounding the coating system, and wherein a protective sheath surrounds the tight-buffered optical fiber.