Ultra-low frequency oscillation( ULFO) has been the most common problem of frequency stability in Southwest Power Grid in recent years. The existing researches point out that the governor system is the key factor to cause the UFLO.The optimization of governor parameters is an effective way to suppress the ULFO. Besides

the nonlinearity of governor deadband has a great influence on ULFO

and the appropriate setting of governor deadband contributes to the suppression of ULFO.The frequency response system is adopted to analyze the governor deadband of hydro-thermal generation unit

and its influence on ULFO is presented. Adjusting the deadband setting is suggested for purpose of suppressing ULFO while maintaining the system ability of frequency regulation.