New wide-area algorithms for detecting angle instability using synchrophasors

Electric power system is undergoing major technological advances with many new installations of synchrophasors across the North American grid as well in power systems all over the world. Wide-area monitoring system (WAMS) in the Pacific Northwest and the Eastern Interconnection Phasor Project (EIPP) in the eastern grid are examples of such installations. Synchrophasors together with modern communication technology facilitate the monitoring of the current state of the power system including the phase angles of the bus voltages at critical buses in a time-synchronized fashion. Power system operation is constantly facing contingencies such as from line faults and generator outages. For operational reliability, the system must be able to withstand all credible contingencies, either by itself (for N-1 contingency) or with the help of Special Protection Schemes (SPS) or Remedial Action Schemes (RAS) (for N-2 or worse contingencies). However, when the system is operating under unforeseen conditions or under unusually high stress, the system can experience the angle instability. In that case, the system breaks up into many islands, resulting in large loss of loads and generations and a potential blackout scenario. In this paper, new algorithms are proposed for detecting the emergence of angle instability phenomenon while it is still evolving so that suitable countermeasures can be initiated to prevent the islanding. The proposed algorithms and the controller detect the fast separation of phase angles among the critical areas automatically by using the synchrophasors, and proceed to mitigate the instability by suitable switching action. Briefly, the algorithms initiate tripping of critical generators in the accelerating part of the system when necessary, and also initiate load shedding in the decelerating part of the system whenever necessary. The novelty of the algorithms is in the fact that all the decisions are made in real-time purely based on the wide-area synchrophasor measurements without any knowledge of the details of the relay actions that may have resulted in the angle stability phenomenon. The concept of a real-time transient energy function method for the large power system is also explored to solve the problem. The paper will discuss the new algorithms along with illustrative examples on standard IEEE test systems.