This work studies the non-conventional ferroresonance oscillation in the 275kV substation. Voltage transformer (VT) which is used in this substation has a 100VA capacity and magnetization characteristic of it was modeled by single-value two-term polynomial with q=7. In this study, at first ferroresonance oscillation in VT has been introduced, then effect of Metal Oxide Varistor (MOV) on limiting these nonlinear overvoltages is investigated. It has been shown for some parameters values, MOV cannot control the ferroresonance. So, by connecting the neutral earth resistance (NR) to the system grounding, non-conventional oscillation has been controlled for all value of system parameters. Simulation results show that considering neutral earth resistance exhibit great controlling of ferroresonance overvoltages. It is also shows by using this resistance, system exhibit less sensitivity to the changing the parameters value of the power system.