Behavior of the Digital Fourier Transform as Numerical filter in Distance Protection of Series Compensated Transmission Lines. Simulations With a Real Transmission System

In this paper, a MATLAB model of a Digital Fourier Transform (DFT)-based digital distance relay was developed and then its behavior was analyzed when it is applied on distance protection of a real series compensated transmission system, belonging to the Chilean generation and transmission utility Colbún S.A. The complete signal processing and the impedance calculation of real relays are simulated by the model. The transmission system was modeled with ATP and various fault types at buses and diverse line locations were simulated. The DFT-model response was evaluated in each fault case from the obtained current and voltage signals. The results show how series capacitors impact negatively on the impedance calculation using DFT.