Development and field test evaluation of optical current and voltage transformers for gas insulated switchgear

An optical current transformer (CT) based on the Faraday effect and an optical potential divider (PD) based on the Pockels effect, for application to electric power systems, are described. This optical CT is suitable for highly reliable gas insulated switchgear (GIS), and has free space light transmission parts among the optical fiber signal transmission lines. The developed optical CT and PD were built into 77/ square root 3 kV 1200 A single-phase prototype GIS. Their basic characteristics of current and voltage measurement conformed well with the standards of the JEC (Japan Electrotechnical Commission) 1201 for instrument transformers. A long-term field test of the prototype GIS was carried out at a substation for 20 months, during which time no significant variation of current and voltage measuring characteristics was observed.<>