Optical technique for measurement of current at high voltage

Consideration is given to the design of an optical device for the measurement of current at high voltage based on the Faraday magneto-optic effect in flint glass. A laser beam directed upward from the ground passes through the free atmosphere to interrogate a passive transducer situated on the high-voltage line. The beam is then reflected down to a ground-based detector system. The investigation has been directed, in the first instance, towards the provision of a versatile research tool for the analysis of disturbed-line conditions, although, ultimately, such an arrangement could obviate the necessity for the expensive and bulky insulation found in conventional current transformers. This is particularly relevant in view of the trend towards higher transmission voltages. The appropriate design features are considered in some detail. Their implementation in a prototype device is also considered. The bandwidth of the prototype device was from direct current to 2 MHz, and its dynamic range for less than 5% nonlinearity was 10–12000 A (these figures are not fundamental and can be varied). The device promises to provide a cheap, accurate and robust current-measurement system for various applications in power-transmission networks.