Seismic Performance Analysis of ±800kV UHV Delta-connection Converter Transformer System

Convert transformers are important components in the ultra-high voltage (UHV) converter substation, serving to convert the AC voltage into the commutation voltage for the converter. In general, the converter transformer group have two connection forms, the delta connection and the star connection, which can realize twelve-pulse commutation. However, if the connections are not sufficiently flexible, significant dynamic interaction may occur between the interconnected bushings during the earthquake, which can result in great damage of the converter transformers. In order to investigate the seismic performance of the ±800kV UHV delta-connection converter transformer system, three earthquake records are adopted as the input ground motions, and dynamic time-history is analyzed on two finite element models of a single transformer and the delta-connected converter transformer system were performed in this paper. Results of the numerical study show that the connection can reduce the fundamental frequency of the lower valve-side bushing and increase its displacement response during the earthquake. Moreover, the connection can increase the top acceleration, top displacement, and root stress response of the upper valve-side bushing, with displacement and stress response increased by more than 40%.