en Measurements Measurements Research Paper Research Paper <div style="text-align: justify;"><span style="color:#000000;"><span style="font-family:Times New Roman;"><span style="font-size:14px;">In this paper, a novel approach based on the Th&eacute;venin tracing is presented to modified conventional impedance-based out-of-step (OOS) protection. In conventional approach, the OOS detection is done by measuring positive sequence impedance. However, the measured impedance may be change due to different factors such as capacitor bank switching and reactive power compensators that it can cause the relay to malfunction. In this paper, first, an on-line Th&eacute;venin equivalent (TE) approach based on the recursive least square (RLS) is presented. Then, a protection function is developed based on online network Th&eacute;venin equivalent parameters to correct the measured impedance path. The main feature of this method is the use of local voltage and current measurements for Th&eacute;venin equivalent estimation and OOS protection. The performance of the proposed method is investigated by simulation of synchronous generator OOS protection function in the presence of a static synchronous compensator (STATCOM). The simulation results show that, STATCOM changes the impedance path and can cause the incorrect diagnosis of OOS relay. Furthermore, the proposed method corrects the impedance path and improves the accuracy of OOS impedance-based function when the STATCOM is installed in system.</span></span></span></div> Thévenin Equivalent, STATCOM, Out-of-Step Protection, Synchronous Generator. 1690 1690 http://ijeee.iust.ac.ir/browse.php?a_code=A-10-1705-2&slc_lang=en&sid=1 S. R. Hosseini sr.hosseini@aut.ac.ir 180031947532846009469 180031947532846009469 No Depatrment of Electrical Engineering, Amirkabir University of Technology, Tehran, Iran. M. Karrari karrari@aut.ac.ir 180031947532846009470 180031947532846009470 Yes Depatrment of Electrical Engineering, Amirkabir University of Technology, Tehran, Iran. H. Askarian Abyaneh askarian@aut.ac.ir 180031947532846009471 180031947532846009471 No Depatrment of Electrical Engineering, Amirkabir University of Technology, Tehran, Iran.