Power System Monitoring and Control

8Wide-Area Measurement-Based Emergency Control

To prevent power system blackout following a severe contingency, an emergency control action may be needed. Serious load generation imbalance, which is usually the result of a severe contingency, may lead the system to cascading failures and even blackout. Load shedding (LS) is a well-known emergency control scheme used to curtail the loads that could not be supplied in an acceptable time duration, before loss of the remaining power. A general review on the role of disturbance size/location, shed load block size/location, and shed delay time in the effectiveness of LS actions shows that a wide-area LS approach is expected to be a useful solution candidate for developing LS schemes to offer better coordination (considering cascading failures).

Frequency and voltage are more frequent decision indices in the emergency control strategies. Most LS schemes proposed so far separately use voltage and frequency information via underfrequency and undervoltage LS (UFLS/UVLS) schemes. Furthermore, the underfrequency and undervoltage relays usually work in the power system without any coordination. In this chapter, the necessity of considering both voltage and frequency indices to achieve an effective and comprehensive LS strategy is emphasized. It is also clarified that this problem will be more dominant for a wide-area power system with renewable energy sources (RESs) such as wind power turbines.

In the present chapter, after a background ...