With the continuous increase of the renewable energy integration scale and the delivery demand

the problem of heavy load and congestion in the transmission system tends to become more severe. This situation demands higher standards for the refinement of power grid construction schemes. Based on the refined modeling of substation construction engineering

this paper proposes a transmission system planning method that considers both substation and transmission network construction. This method expands upon the traditional planning theory

which mainly focuses on grid network construction. First

the method of connection on both the high-voltage and low-voltage sides of the new substation is modeled. Furthermore

a bi-level model of transmission system planning and checking is constructed. The upper level establishes a system model for substation and transmission line planning

considering the constraints of planning comparison and construction timing logic. The lower level considers the operation simulation in typical and fault scenarios simultaneously

ensuring that the planning results can meet the operation requirements in typical scenarios and adhere to the constraints for safe operation in fault scenarios. Finally

the effectiveness of the proposed method is verified based on the modified Garver's 6-bus system and an actual power grid case.