This paper studies the effect of zinc oxide arrester (ZnO) and neutral earth resistance on controlling nonconventional oscillations\r\nof the unloaded power transformer. At first, ferroresonance overvoltage in the power system including ZnO is investigated. It\r\nis shown this nonlinear resistance can limit the ferroresonance oscillations but it cannot successfully control these phenomena.\r\nBecause of the temperature dissipation of ZnO, it can withstand against overvoltage in a short period and after that ferroresonance\r\ncauses ZnO failure. By applying neutral earth resistance to the system configuration, mitigating ferroresonance has been increased\r\nand chaotic overvoltage has been changed to the smoother behavior such as fundamental resonance and periodic oscillation. The\r\nsimulation results show that connecting the neutral resistance exhibits a great mitigating effect on nonlinear overvoltage.
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