Voltage Transformer Ferroresonance in One 400 Kv Gis Substation

This paper is aimed at analysing (i) the circumstances under which forrorasonance is liable to occur in one 400 kV Gas Insulated Substation (GIS) equipped with inductive voltage transformers, and (ii) the means to be applied for either avoiding its appearance or accelerating its damping out. After a concise description of both, the theorethical aspects of the phenomenon and the main characteristics of the substation, the paper outlines the calculating model as well as the various operational connection schemes investigated by making use of the FMTP Program. The various circumstances under which those operational schemes are liable to be driven into farroresonance are analysed and the results concentrated in tables. Two means aimed at avoiding ferroresonance occurence or assuring its rapid damping out are also examined. The insertion of 1 ohm resistance into the secondary of the voltage transformer (in parallel to its load) is considered to be the most favorable solution. This protective measure will be activated only when certain signals are indicating that forroresonance has occurred and is liable to persist.