Real time probabilistic security risk assessment at an EMS

An online risk-based security assessment system-Probabilistic Security Risk Assessment (PSRA) has been developed and implemented at China Southern Power Grid. PSRA calculates the probability or likelihood of each undesirable event in the transmission system and evaluates the corresponding severity. In PSRA, the probability measure of each undesirable event is combined with the consequence measure into a single reliability index-Probabilistic Loss of Load Index. When power system is insecure, optimal generation re-dispatch is implemented to ensure the system goes back to the secure region. Under emergency conditions, when generation re-dispatch alone is not enough, load shedding will be enforced to bring the system back to the security region. Weak point analysis is developed and used to identify the buses and branches that are most vulnerable. Online implementation of PSRA is also discussed and it is concluded that the proposed probabilistic reliability analysis is much more accurate than traditional methods and it provides system operators the capability to make faster trade-off decisions between economy and technical constraints.