Comparison frequency estimation methods on adaptive protection architecture applied on systems with distributed generation

In this paper the performance of three algorithms for frequency estimation is evaluated and they are applied in an adaptive protection scheme (APS) which was proposed to determine the instantaneous overcurrent relay setting. The APS will monitor system modifications done from the estimation of the fundamental frequency. For this, three methods of fundamental frequency estimation such as: (a) zero-crossing, (b) adjustment of points to a pure sinusoidal waveform method (APPSW), and (c) algorithm based on discrete Fourier transform (DFT). Here, these algorithms were applied in distribution systems with distributed generation (DG), and were compared and analyzed the behavior of the APS. The proposed adaptive protection method by frequency estimation was applied in a real Brazilian sub-transmission system, owned by Eletrobrs Distributer of Alagoas (EDAL). APS was built using ATP/MODELS. The evaluation methodology for the frequency estimators is based in statistical error such as mean square error. The DFT based estimator presented better results in comparison with the other evaluated algorithms. Therefore, the application of the DFT method to the adaptive overcurrent protection presented good results of the relays settings and on the protection of the system.