Abstract: In order to solve the difficulty land requisition and high land cost problems for substation and line corridor in high load density regions, this paper put forward a scheme of 220 kV directly step-down to 10 kV to reduce the construction land of power facilities and save the cost of construction. According to the actual situations of power grid in Liaoning, this paper built two kinds of power supply models for 220/10 kV and 220/66/10 kV voltage sequences, and analyzed the technical and economic indicators, including the construction scale, the occupied area, the power supply cost of unit load and the terminal voltage deviation rate of 10 kV line. The results show that the 220/10 kV directly step-down to 10 kV scheme used in urban load center with load density higher than 15MW/km2 can attain better economic benefit. It is suggested that the area selection for directly step-down substation should think over four aspects: the capacity requirements of main transformer, easily 220 kV power supply, no requirement for 66 kV network, and high demand for 10 kV network.

Key words: 220/10 kV, grid model, voltage sequence, load density, voltage deviation rate