The medium-voltage （MV） power systems with high-resistance grounding at the neutral point are becoming increasingly prevalent with the continuous development of ship power systems.Single-phase disconnection fault，a common electrical issue，can cause significant overvoltage in the power systems.This paper analyzes three scenarios of single-phase disconnection fault：disconnection without grounding，grounding at the power supply side of the disconnection point，and grounding at the load side of disconnection point.Considering the factors such as transition resistance at the grounding point，load impedance，and the location of disconnection，the symmetrical vector method is used to derive the analytical expression for zero-sequence voltage before and after disconnection.The relationship characteristics of overvoltages at both ends under different conditions are analyzed based on the theory of inverse transformation and conformal mapping.A typical power system simulation model is constructed to verify the correctness of the theoretical analysis results，providing a theoretical foundation for the precise localization of single-phase disconnection faults in power systems in the future.