RELIABILITY OF OPTICAL FIBRE MEASURING SYSTEMS IN ELECTRICAL POWER INDUSTRY

Sensor development is a new focus for non-telecommunication applications of fibre optic technology. One particular area of activity is in current and. voltage sensing for which envisaged applications are monitoring current flow in transmission lines and in power circuit breakers and in other hostile environments. Fibre optic sensing and transmission has inherent advantages compared with conventional electronic techniques, particularly immunity to electromagnetic noise, insulation strength, wide-band response, light weight, compactness and possibly lower cost. To date research on optical fibre current sensors has concentrated on single mode optical fibre systems. The current sensors exploit the Faraday electro-optic effect. This approach suffers from industrial incompatibility, lack of robustness and long term instability (due to the sensitivity of interferometers to both stress and temperature). To overcome these problems ef .iave been made to manufacture special types of optical fibre such as highly birefringent fibres for maintaining polarisation throughout the length of fibres but with little success. Recently a novel technique of modulation referred to as chromatic modulation has been developed at Liverpool which overcomes many shortcomings of other optical modulation techniques. The approach is attractive because of low cost, robustness, ease of manufacturing, installation and calibration, and thus is industrially more acceptable. The optical fibre voltage sensor systems examined here utilise the electro-optic effects (Pockelseffects) as a passive element. Resolutions of up to 1 in 104 were achieved, corresponding to a resolution of 0.9 V from 0 to 14 KV for systems based on the Pockels effect. Immunity of the prototype systems to environmental perturbations are demonstrated indicating the compatibility of this approach for harsh environments.