The Behavior of WLS State Estimator Near the Maximum Loadability Point of Power Systems

The Jacobian matrix of the power flow equations become singular at the maximum loadability point and problemes of non convergence are observed due to ill-conditioning. The Jacobian of the state estimation formulation also becomes singular at the maximum loadability point and problems with state estimator convergence are expected. In this paper, the behavior of the WLS-state estimator in the neighborhood of the maximum loadability point is investigated. The results indicate that low levels of redundancy of the measurement set may lead to increased problems of convergence in the neighborhood of the maximum loadability point. But worst than that, average estimates of the total load that are lower than the real load are also observed. This behavior may lead operators to make non conservative estimates of load margin and allow the operation in non secure states.