Optical fibre current measurement system using liquid crystals and chromatic modulation

A novel monitoring system has been developed for the measurement of electrical current in power systems. A sensor which incorporates active electronic components is sited on the power line. Power for these components is derived from the line itself. However, owing to the low power consumption, the sensor operates from line current levels as low as 3 A. An optical link is used to convey measurement information derived from the power line to a remote site, resulting in electrical isolation of the site from the line. The sensor uses liquid crystal elements to transduce a voltage related to the line current into an optical signal. This information is encoded in the form of chromatically modulated light. Particular attention has been paid to the problem of liquid crystal temperature sensitivity with the implementation of a liquid crystal matrix modulator