Preliminary study on optical differential protection of transmission line

An all-fiber optic current transformer measures current in the conductor according to Faraday magneto-optic effect, with a wide measuring range, excellent nonlinearity and no magnetic saturation. Since the magnetic field effect of the current can be superimposed, measurement of differential current from transmission line with sensing optical fiber can be replaced by direct calculation of Faraday magneto-optical effect deflection angle at the level of optical path with optical components, which means differential current of the transmission line can be acquired without complicated time synchronization to constitute differential protection. An optical differential protection model is built with PSCAD, the simulation results showing using the optical differential protection to measure differential current can reflect the variation of actual differential current while optical differential protection using fixed threshold value has a higher sensitivity to fault in the area and definite reliability for one outside.