en 1-Distributed Generation Distributed Generation Research Paper Research Paper Identification of intentional and unintentional islanding situations of dispersed generators (DGs) is one of the most important protection concerns in power systems. Considering safety and reliability problems of distribution networks, an exact diagnosis index is required to discriminate the loss of the main network from the existing parallel operation. Hence, this paper introduces a new islanding detection method for synchronous machine–based DGs. This method uses the average value of the generator frequency to calculate a new detection index. The proposed method is an effective supplement of the over/under frequency protection (OFP/UFP) system. The analytical equations and simulation results are used to assess the performance of the proposed method under various scenarios such as different types of faults, load changes and capacitor bank switching. To show the effectiveness of the proposed method, it is compared with the performance of both ROCOF and ROCOFOP methods. Islanding Detection,Non-Detection Zone,Passive Methods,Synchronous Machine-Based Distributed Generation, 94 106 http://ijeee.iust.ac.ir/browse.php?a_code=A-10-876-1&slc_lang=en&sid=1 M. Bakhshi bakhshi.mohsen@gmail.com 180031947532846003022 180031947532846003022 No Department of Electrical Engineering, Zanjan University, Zanjan. R. Noroozian noroozian@znu.ac.ir 180031947532846003023 180031947532846003023 Yes Department of Electrical Engineering, Zanjan University, Zanjan. G. Gharehpetian grptian@aut.ac.ir 180031947532846003024 180031947532846003024 No Amirkabir University of Technology, Tehran , Iran