Low-power optical current measurement system employing a hybrid transmitter

Abstract

A high-performance current measurement system has been developed for use in power systems. Active electronic components are sited in a transmitter on the power line, with power for these components being derived from the line via a current transformer(CT). Measurement information is transmitted to the remote receiver by an optical fibre, which provides electrical isolation from the line and immunity to the electromagnetic interference commonly present in such installations. The optical fibre also allows the transmitter to be sited up to kilometres from the receiver. A current transformer is used to derive measurement signal proportional to the line current. The active circuit, in conjunction with a pulsed frequency modulation optical transmission system, achieves new standards of performance for low power consumption. Thus the transmitter will operate from line currents of less than 1 A. The CTs used in the transmitter are subject to different design criteria from those used in conventional CTs, and particular attention is paid to optimised designs for both types of CT.