Contingency ranking for voltage stability analysis of large-scale power systems

In this paper we propose a screening method and suitable software program to analyze contingencies and their impact on static voltage stability in large power systems. The program substantially reduces the number of load flow simulation for contingency analysis and voltage stability studies and is based on the impact of the contingency on the load, and the available Mega Watt Margin (MWM). The program provides initially a ranking scheme for first and second level contingencies by comparing their loadability with the maximum loadability of the system. It then makes a short list of important contingencies for detailed analysis. Contingencies that result in a larger reduction of maximum loadability are placed in Unacceptable Contingency Category, whereas, the contingencies pertaining to smaller reduction are put in Acceptable Contingency Category. The contingencies falling in between acceptable and Unacceptable categories are termed as Significant Contingencies and are placed in third category. The proposed method is tested first by the IEEE 118-bus Test System, and then is applied to study a large-scale real power system with 25,000 buses. The program considers the var limit of the synchronous generators and switching scheme for the capacitor banks.