New smart approach for a U/I-measuring system integrated in a GIS cast resin partition (NCIT) - design, manufacturing, qualification and operational experience

Abstract:
NCIT-Technologies for high voltage Gas Insulated Switchgear (GIS) GIS solutions with non-conventional Instrument Transformer (NCIT) as integral parts of applications with process bus according to IEC 61850 came enhanced in the last decade on the market. New low-signal sensor interface with digital data output to process bus and significantly smaller dimensions and weight of NCIT opened the door to optimized GIS design and to innovative concepts for smart or digital substations. For testing of the functionality of new measurement technology under real operation conditions and for exploring its benefits interested utilities and NCIT manufacturer agreed on manifold pilot projects. One of such pilot projects for a 110 kV GIS substation equipped with parallel operated conventional and nonconventional instrument transformer from German GIS manufacturer was realized in an innovative company responsible for the electricity transmission in the high-voltage transmission system in 2016/2017. In order to get a long-term experience and comparison of measured current and voltage values between both measurement technologies special monitoring system for permanent recording was installed in addition to the GIS components needed for the usual operation and protection. Via vpn-communication channel measurement data gained and recorded in the substation has become available in head quarter of the utility and at the research centers of NCIT manufacturer in Germany. Common strategy was agreed between the utility and GIS manufacturer for evaluation, comparison of results and feedback during the long-term observation of technology. Deeper investigation of the measurement behavior of NCIT sensors has become possible in the early stage of the operation due to some unexpected earth-faults occurring in the overhead lines of substation. Dynamic, transient changes in primary voltage and current measured during the faults both by the old and by the new transformer technology were recorded and evaluated offline. Comparison of measurement behavior of both technologies during the grid faults brought valuable results in addition to the numerous records from usual steady-state grid operation. This paper describes the approach for integration of NCIT in the high voltage GIS and brings an overview about NCIT application in real operation conditions in pilot project in utility. Publication of deeper results of NCIT pilot application is planned for next CIGRÉ session in Paris 2018.