An Improved Method for Determining Line Discharge Through Potential Transformers

Potential transformers of inductive type have proved to be efficient in discharging lines within the dead time of three-phase automatic reclosure. An accurate computer simulation of this discharge process requires knowledge of the actual non-linear flux-current relationship of the potential transformer intended for use. With an experimental method described in the paper, this relationship is determined with high accuracy, and thus discharge is computed on realistic basis. Effect of line length and primary winding resistance is analysed, and the conclusion is drawn that with the use of the 400 kV potential transformer investigated, the overvoltage level of the network is materially reduced.