Two electrooptic methods for measurement of DC currents at high voltage level, extending from the nA range and up to the milliampere range have been developed. First, by switching the polarity of a measured DC voltage into a Pockels cell, DC currents can be measured and transmitted along an optical fibre to an electrooptic converter. Second, by use of an electronic circuit the measured signal can be converted into a modulated frequency form for transmission along an optical fibre. These systems are described, measurement results are presented and improvements to be made in the future are outlined. The measuring methods can be used both for development and supervision of electrical insulating systems. For DC measurements a system wherein the voltage is applied (across the Pockels cell) not directly but via an electrooptic circuit was developed. This circuit periodically inverts the polarity of the voltage across the cell, effectively applying a square wave voltage with amplitude equal to the DC voltage to be measured. The switching circuit is based around two high voltage transistors TA, TB, with the Pockels cell electrodes being each connected to one of the transistor collectors. The transistor collectors are connected via resistors RA and RB to the protective side of the voltage to be measured and the emitters to the negative side. The currents flowing in to the bases of the transistors are independently controlled by the light levels following on the two photodiodes PDA, PDB.
Bibliographical noteCopyright: 1989 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE
Tønnesen, O., Beatty, N., & Skilbreid, A. O. (1989). Electrooptic Methods for Measurement of Small DC Currents at High Voltage Level. I E E E Power Engineering Review, 9(7), 41-42. https://doi.org/10.1109/MPER.1989.4310789