Expanding the measuring range via S-parameters in a EHV voltage transformer modelling for reliable GIS VFT simulations

Abstract

The customary approach to modelling voltage transformers (VT) at gas insulate substations (GIS) subject to Very Fast Transients Overvoltages (VFTOs) consists of using a capacitive element. However, this simplistic approach is unable to reproduce characteristic resonances and predict how transients propagate to the VT’s secondary winding. Multiport black-box passive rational models built upon frequency-domain measurements are instrumental to overcome these challenges. The adoption of S-Parameters is an alternative to black-box approaches based on Y-Parameters so as to consistently expand the measurement frequency range which is required to accurately capture the dynamics involved in VFTO phenomena up to 50 MHz at GIS facilities. We validate our results using an strategy that entails measuring, modeling and simulation upon a multiport extra-high voltage (EHV) VT. The proposed approach using S-Parameters leads to increased accuracy compared with the customary approaches using Y-Parameters or capacitive elements.We build two models estimated upon distinct frequency ranges to highlight the importance of extending the measurements into the MHz range so that time-domain simulations better reproduce VFTO characteristics. The black-box VT model thus obtained is incorporated into an actual 500 kV GIS model for transient simulations enabling the analysis of transient propagation between primary and secondary windings.