Hybrid Optical Voltage and Current Combined Instrument Transformer

Instrument transformers (IT) are used for protection and metering in energy distribution networks. Especially for the high and highest voltage levels the application of optical technologies seems to be advantageous due to its inherent electrical insulation by optical fibres which helps to avoid any electromagnetic compatibility (EMC) related problems caused by the inductive and capacitive coupling between the high voltage distribution level and the secondary metering. This issue becomes even more important as secondary relays are based on digital electronic equipment. This paper presents a combined instrument transformer for voltage and current measurements. The voltage measurement is based on the optical Pockel’s effect whereas the current measurement comprises a low power inductive current sensor and an optical transmission link. Furthermore, the international standards for electronic instrument transformers are referenced. The IT´s performance in terms of accuracy is discussed. The main goal of the presented approach is the combination of high reliable measurement technologies and economic insulation coordination.

Keywords:

Distributed Pockel’s Crystals , Digital Optical Data Transmission