An Empirical Criterion for the Convergence of the Fast Decoupled Load Flow Method

This paper presents a study of the reliability and convergence characteristics of the rast Decoupled Load Flow (FDLF) method. The results presented in the paper clearly show that the reliability of the FDLF mcathod cannot be taken for granted for systems having lines of large R/X ratios and/or capacitive series branches. An empirical criterion for testing the reliability of the FDLF method for any given system is proposed. This involves the estimation of a scalar con stant from the given system parameters. It is shown that the magnitude of this constant is correlated to the rate of convergence of the FULF method and the convergence could be expected only when the constant is less than unity. Results oF studies on a large number of test cases are prpsented in order to validate the proposed critprion. In addition the results presented in the paper provide significant information on a number of aspects of the behaviour of the FDLF method.