In debugging process of 168 h trial operation for unit no.2 in second-phase project of Bashu Jiangyou Power Plant(2×300 MW units)

power oscillation had appeared

resulting in abnormal fluctuation of power and voltage in a large region of 500 kV power grid in Sichuan Province.Through analysis

it is believed that the causes leading to above-mentioned abnormal fluctuation of power and voltage are as follows:(1)in the stage of sliding parameter operation for starting up the unit

the valve-position control mode was used

and the governing valve being put into the "whole open"position

the target value of load being too high;(2)the slope of original low excitation limit curve was too large;(3)after occurrence of fluctuation

the reactive load hadn't timely increased

on the contrary

the active load of the unit was still increasing.Regarding to this

the curve of low excitation limit has been modified

and now the unit can keep in stable operation.