An adaptive correction for voltage security analysis using a local approach solution

This paper presents an efficient contingency screening for voltage limit violations. The screening process is based on the local approach solution. A separation in the Q-mismatch calculations between buses situated in the vicinity of the perturbation and buses electrically far away from the perturbation is used. This approach takes advantage of the fast convergence rate of buses that are far from the outaged equipment and allows fast and accurate Q-mismatch calculations. The concept of electrical distance is also used in order to predict the buses in which major voltage shifts can occur after the contingency. The solution usually corresponds to the single iteration of the well known fast decoupled load flow model on which an adequate correction is applied in order to detect all possible contingencies that can cause limit violations. This solution can also be carried out with two iterations instead of the traditional one iteration scan methods. Results of tests with a 206 bus-299 branch 400 kV French network show that CPU time required for two partial iteration scans is almost equivalent to one complete iteration (1P-IQ) of the fast decoupled load flow model. In fact, computation time is saved by using approximate Q-mismatch calculations, by setting small Q-mismatches at zero and by using sparse vector techniques for nonzero mismatches (fast forward, fast back solutions). The number of buses involved for the solution process is drastically reduced especially for the second iteration and accuracy is better than with traditional methods