Unplanned island effect small hydropower station system coping processing method and device

The invention discloses an unplanned island effect small hydropower station system coping processing method and device. The method comprises the steps of controlling a circuit breaker on the high-voltage side of a main transformer between a small hydropower system and a main power grid to be disconnected after monitoring that the main power grid fails, measuring to obtain exchange power between the small hydropower system and the main power grid, and determining that the absolute value of the exchange power is smaller than or equal to electromechanical group regulation limit active power in the small hydropower system, if the reactive exchange power between the small hydropower station system and the main power grid is smaller than or equal to the electromechanical group regulation limit reactive power in the small hydropower station system, obtaining the frequency change off-limit time of the exchange power, determining that the frequency change off-limit time is smaller than the electromechanical group regu