Abstract: Following the change of time and technical measures, some hidden troubles in the hydropower station transformer, such as the malpractices and its harmful aftermath in the main connection mode and the transformer operation, and the overtension of the terminal voltage and the auxiliary power, were emerged, it is necessary to reform aiming at deferent status. This paper analyzed the reform reasons of the hydropower station transformer, and proposed the optimum reform plan.

Key words: hydropower station transformer, main connection mode, overtension, optimum reform