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

A deformation monitoring method for measuring at least tensile strain of at least one electric cable, comprising:

• providing at least one electric cable comprising a strain sensor longitudinally extending along the cable and comprising a single mode strain optical fibre arranged within a bending neutral region surrounding and comprising a bending neutral longitudinal axis of the electric cable, a strain-transferring filler, and at least three longitudinal structural elements, at least two of the at least three longitudinal structural elements being a core comprising an electrical conductor, wherein the strain sensor is embedded in the strain-transferring filler mechanically coupled and congruent with the at least three longitudinal structural elements at least in a strained condition;
• injecting a first optical signal into the strain optical fibre;
• detecting Brillouin scattered light emitted from the strain optical fibre;
• and
• analysing the spectral changes in the scattered light so as to measure at least the tensile strain of the at least one electric cable.

A deformation monitoring system for measuring at least tensile strain of a plurality of electric cables comprising:

• a sampling apparatus for measuring spectral changes of Brillouin scattered light comprising a first and a second optical input/output port, the first input/output port being capable of emitting a first optical signal and the second input/output port being capable of emitting a second optical signal;
• and
• a first plurality of electric cables comprising a first and a last electric cable, each cable of the plurality comprising a strain sensor comprising a strain optical fibre and a temperature sensor comprising a temperature optical fibre, the strain and temperature sensors extending longitudinally along a respective cable, the strain optical fibre and temperature optical fibre having proximal ends and distal ends, the proximal ends being positioned at a proximal end of the respective electric cable, wherein:
• the distal ends of the strain optical fibre and the temperature optical fibre of each electric cable are optically connected one to another,
• the proximal end of the strain optical fibre of the first electric cable of the first plurality is in optical communication with the first input/output of the sampling apparatus and the temperature optical fibre of the last electric cable of the first plurality is in optical communication with the second input/output port of the sampling apparatus, and
• the proximal end of the temperature optical fibre of the first electric cable is optically connected with the proximal end of the strain optical fibre of the last electric cable, so as to form an optical fibre loop in which the strain optical fibre and the temperature optical fibre of each electric cable of the plurality are in optical communication with both the first and the second input/output ports of the sampling apparatus and the first and second optical signals enter the optical fibre loop in opposite directions, wherein:
• each electric cable of the first plurality of electric cables comprises at least three longitudinal structural elements, at least one of the at least three longitudinal structural elements being a core comprising an electrical conductor, the strain optical fibre of each heavy-duty cable being arranged within a bending neutral region surrounding and comprising a bending neutral longitudinal axis of the cable, a strain-transferring filler, and the strain sensor is mechanically coupled with at least one of the at least three longitudinal structural elements.