In a neutral nongrounding power system, the excitation impedance of an electromagnetic potential transformer (PT) and a ground capacitance power transmission line of an electric power system can form a resonant circuit that causes ferroresonance and endangers the security and stability of the power system. This study analyzes a theory of ferromagnetic resonance that occurs under a single-phase earth fault in the power system of a PT, and Simulink is used to establish a simulation model of PT ferromagnetic resonance. Through this model, Simulink conducts an analysis of the ferromagnetic resonance simulation for the isolated operation of an ordinary PT and a low magnetic flux density-type PT, the parallel operation of these two PTs, and the parallel operation of two low magnetic flux density-type PTs. Simulation results show that ferromagnetic resonance phenomenon does not occur easily in a PT with good excitation characteristics. However, ferromagnetic resonance can be generated easily in PT parallel connections.