Stability Analysis of Power System with Under-excitation Limiter in Generator Excitation Control System

The objectives of setting under-excitation limiter (UEL) of generator excitation control system are to prevent excessive stator end-core heating and to prevent the generator from operating beyond the steady state stability limit when the generator operates in the leading reactive power region. But many oscillation cases caused by UEL happened in power system recently. This paper analyses the impact of important parameters of UEL to the system dynamic stability in-depth by using electromagnetic torque analysis method and time domain simulation method. It is concluded that the root causes of system oscillation are the negative damping provided by UEL and the effect of weakening the damping of PSS by UEL. The effective control strategy of optimizing the parameters of UEL to improve the system damping is proposed, which provides an important reference for good performance of UEL.