Analysis of Converter Transformer Failure in HVDC Systems and Possible Solutions

An HVDC transmission system has a converter transformer as one of its main components. The failure of the converter transformer is one of the major concerns for electric power utilities all over the world. Invariably, the top portions of the secondary windings of the converter transformers fail whereas the primaries are left unaffected. In this paper, an effort has been made to analyze the causes for these failures by means of modeling a practical HVDC system existing in India which ties up Talcher and Kolar and has a length of 1368 km. The modeling and analysis have been carried out in the MATLAB/SIMULINK environment. Based on the analysis, possible solutions for this problem have been suggested, such as providing passive filters on the secondary windings of the converter transformer, connecting a parallel capacitor on the do side of the converter and R-C snubbers across the secondary windings. The suggested solutions have been compared to bring out their relative merits and demerits.