摘要
Introduction In recent 10 years, due to fast developing of economy inChina, serious power shortage occurs. The system frequency oftenfell to abnormal values in most networks. For the security of powersystems, forced switch off of feeders from the distribution substationoften happend to recover normal frequency. In fact, the speed of development of Chinese power industryis very high in this period. The yearly average increasing rate ofgenerating capacity was about 8%. The yearly newly installed ca-pacity was more than 9000 MW in recent 4 years. But the
