Qualitative insights into the voltage stability problem

This work investigates some of the bus indicators for the problem of voltage stability. The purpose is to learn more about the behavior and to observe the factors that cause mis-ranking in estimating the stability margin. Three indicators are examined, the L-index, the coupled-port method, and the P-index. it found that the L-index does not have a reliable alarm level, and when flagged with an alarm used for the P-index, it shows a large variation of the estimation accuracy across systems. Also, the coupled single-port method is a reformulated L-index method with no novelty on estimation, the novelty is only in the presentation. Finally, the P-index is examined and found to be more reliable if it coincides with a maximum P-index and greater participation in the collapse mode. This is tested on benchmark systems; the results indicate that this approach leads to a better estimation in many cases