Abstract: As the characteristics of high penetration of renewable energy and high proportion of power electronics in power systems become increasingly prominent, issues such as uneven power flow distribution and constrained transmission sections have become more pronounced. The Suzhou power grid faces a structural contradiction between the demand for zonal interconnection and short?circuit current control, which hinders the effective utilization of existing substation capacity. Taking the 220kV Wujiang zonal power grid as an example, this paper proposes an application scheme for phase?shifting transformers (PSTs), conducts optimal configuration of key parameters including impedance and phase?shift angle, demonstrates their power flow regulation capability, and establishes a comprehensive evaluation index for power supply capacity. The results show that PSTs can enable inter?zonal power mutual support while maintaining short?circuit current levels within acceptable limits, thereby effectively unlocking the potential of existing transformer capacity. The findings provide a technical reference for the planning and upgrading of zonal power grids in regions with high load density.