Voltage Distribution in Multi-Cascaded Transformer

Abstract

Voltage distribution for lightning surge in multi-cascaded transformer, that will be used for a converter transformer in self-excited DC transmission, was studied using model transformers. There was good agreement between measured data and calculated results. It was cleared that our calculation program have enough performance for estimating voltage distribution.
Maximum voltages in high-voltage windings for lightning surge were below 120% and transfer voltages to converting circuit were below about 5%. Therefore, there were no serious problems in cascaded transformers for lightning surge. However, their voltage distribution was not satisfactory when same transformers were connected in cascade. We clarified with simulation that the distribution could be improved by modifying every transformer's structure according to position in cascade connection.