Development trends in medium- and high voltage technologies for measuring systems, filters and bushings

Abstract

This paper is a continuation of my paper presented at the Joint Conference of IEEE/CSEE in Beijing / China 1987 development Trends in the Technologies of High Voltage Components for AC and DC Transmission Lines and Substations. The magnetic current transformer (CT) and the inductive (VT) and capacitor transformers (CVT) have had an excellent performance during the last 100 years. Important improvements were the introductions of the fine graded capacitive bushings for CTs/VTs, the stress calculation for CTs/VTs and the first IEC standard of CVTs. Due to its high reliability, the capacitor transformer (CVT's) is used to 90% for measurement. The convenor of the first IEC standard 60044-5, 1st edition 2004-04, is the author of this contribution. A short introduction in the theories for semi conventional current transformers (CTs) with iron-core coils and air-core coils with voltage output is given in this paper. The application is based on the IEC standard 60044-8,1st edition 2002-7. R- and RC-divider will be the sensors (VTs) in the future. The application in medium and high networks is for metering, protection, diagnostics and power quality measurements. The transient performance and the requirements for quality power management cannot be fulfilled by VTs and CVTs. The compensated R- and the RC-divider are today the superior systems for all requirements in GIS and open-air substation. The reliability has been proved during the last 30 years. The IEC standard 60044-7, 1st edition 1999-12, is the tool for application of the new sensors in medium- and high networks. In DC and AC networks, LC-filters are common circuits for the reduction of harmonics in high systems. The specified requirements in the IEC standard 60358, 1st edition 1990, for high capacitors (coupling capacitors) and capacitor dividers do not give enough information regarding the requirements of filter capacitors for the reduction of higher harmonics. The trend for this application is: Improved design of capacitor elements for high harmonic currents and a 2nd edition of the IEC standard 60358 with new requirements and the introduction of chopped wave impulse tests with multiple chopping gaps. High bushings are key components for power transformers, SF6-gas insulated substations (GIS), connection between power transformers and GIS and dead tank circuit breakers. Three technologies are used for the high bushings:The trends in the last 15 years were to improve the transient performance of bushings and to reduce the risk of high breakdowns between the bushing oil end-shielding and the turret.