Power System Stability Control Study Of The Third Line Of Defense

The emergency control for preventing widespread blackout, i.e., the third line of defence(i.e., breaking off out-of-step state, preventing voltage and frequency collapse), under extremely severe disturbance of power system is discussed in this paper. Based on the summarization of previous work .analysis on the out-of-step operation of power systems and study on the load frequency regulation factor have made. In chapter 3, a method that it dopes out the integral value of reactive power in one period of Out-of-step center and compares with the value of the two ends is proposed for capturing the interface of out-of-step by cooperation. In chapter 4, it's testified that u cos φ has the ability to reflect the lowest voltage magnitude in the interface tie lines of out-of-step in the power system. An advantageous system separation activation criterion and a new out-of-step splitting device based on the characteristics of the curve of u cos φ are proposed, also a discussion about the method of distinguishing the fault and the power swings based on u cos φ is made. In chapter 5, a new method of optimizing the Underfrequncy load shedding(UFLS) has been developed. The main idea is that on the basis of the on-line measurement of the load frequency regulation factor, the load with smaller frequency regulation factor is cut off earlier than those with lager frequency regulation factor in the basic load shedding but otherwise in the restoring load shedding. Therefore the power balance will be achieved more quickly in the transient process.