Abstract:Abstract: At present,in river basin development mode,the small hydropower stations such as power source stations in construction period depend on the large hydropower stations of main stream to integrate with main power grid together in later stage. The especial operating mode is the small hydropower station working with long lines alone,so the corresponding configuration measures are put forward to eliminate the self - excitation of small hydropower through the over - voltage electromagnetic analysis of a power source station during construction when accessing to power grid.