Describe in detail an arrangement for measuring the electric current in a high voltage conductor, making use of the Faraday magneto-optic effect in a single-mode optical fibre. Discuss the advantages and disadvantages of the arrangement.
A length of single-mode fibre is wound ten times around a former of radius 1 m which encloses a copper conductor. Linearly polarized light of wavelength 633 nm is launched into one end of the fibre. What magnitude of rotation of the polarization direction has occurred when the light emerges from the fibre at the other end if a current of 100 A is passing through the conductor? What is the maximum current which can be measured without ambiguity? (the Verdet constant for the fibre material = 5.3 x 10-6 radians A-1 at 633nm.)