Optical fibre line current measurement system

Optically coupled current measurement systems obviate the need for the large amounts of insulation required in high voltage CTs and usually allow the sensor to be sited hundreds of metres from the receiving end. The sensor described in the paper uses less power than previously reported hybrid systems which allows operation from a minimum line current of 3A rms. Chromatic modulation is used in which a continuous wide range of wavelengths is used with the measurement information encoded on the spectral signature of this optical signal. The advantages of the chromatic modulation technique include intensity independent modulation, high optical efficiency and high sensitivity. The block diagram of the current measurement system is shown. A broad band light source is used to optically activate the system. This light source addresses liquid crystal elements via an optical fibre