In recent years, based on the growing importance of clean energy in comparison with conventional energy production from fossil fuels, DG systems are gradually becoming more popular all over the world. These resources solve many problem of system. However, these resources create some other problems too. One of the most problem of DGs is unwanted islanding. This paper addresses reliable passive islanding detection algorithm based on the change of positive sequence (ROCOPS) of voltage signal analysis method. At first, all possible linear and nonlinear load switching, motor starting and capacitor bank switching is simulated. The ROCOPS signal of these conditions is measured for all conditions. From of these data, the reliable value of ROCOPS based on thresholding is calculated. The studies reported in this paper are based on time-domain simulations using MATLAB, and the feasibility of the proposed method is evaluated with an experimental system. The experimental system is a test system that impalement for islanding condition detection. The results show that the proposed islanding detection method succeeds in detecting islanding both in the experimental and simulated systems with negligible Non Detection Zone (NDZ). تفاصيل المقالة