Development of an Adaptive Underexcitation Limiter in Excitation System

A generator is designed to operate in the underexcitation region within its capability according to the system conditions. However, a sustained underexcitation condition owing to the partial and complete loss-of-field in the generator can cause thermal damage and system instability. Thus, an automatic voltage regulator and an underexcitation limiter should control the underexcitation condition of the generator, and the loss-of-field relay should be utilized to guarantee reliable operation. Therefore, in this paper, we discuss the coordination of generator underexcitation protection among various factors. In addition, in order to enhance the conventional underexcitation limiter, we proposed an adaptive underexcitation limiter. Through this method, a possibility of miscoordination can be avoided and the operation is modified adaptively according to the loss-of-field condition. The performance of the proposed method was verified via a 345-kV Korean nuclear power plant and transmission system using the Electromagnetic Transients Program.