Dynamic Security Assessment to protect systems after severe fault situations

In the last 10 years the number of severe fault situations and black-outs world wide is increasing. The classical static security assessment is used to monitor the system situation after contingencies, but is not able to take into account the complex dynamic behaviour of an electrical system together with the control of generators and grid equipment like switched capacitors or FACTS together with the protection reaction in unforeseeable situations after severe system faults. The paper describes a modern dynamic security assessment (DSA) system which allows handling predefined dynamic contingencies in real-time and intelligent proceeding and evaluation. The base of the system is the system simulation tool PSStrade NETOMAC, which can simulate the dynamic behaviour of large electrical systems including control and protection. A contingency builder allows the user to define the interesting contingency scenarios like outage of grid elements, generators or combination of outages or system faults like short circuits, etc. The events can be calculated in real time which means, that about 200 contingency cases can be handled in about 10 minutes, depending on the system size. The DSA-system analyses the events using an intelligent and flexible criteria editor which gives the opportunity to select criteria for critical system time behaviour. These criteria allow to observe how critical a system reacts checking under voltages, frequency, angle differences in the grid, overcurrents, machine angle, etc. The information about severe cases is available in a protocol for easy recalculation of critical cases in details with more parameters checked and monitored. The results can be used to monitor the overall situation of a system periodically. The automatic monitoring of critical events is under construction.