Abstract: The operation of the Beijing power grid is divided into zones, and the grounding method used at the hub station has a significant impact on the overall operation of the electrical grid. In the K zone, the A substation adopts the operating mode of grounding the medium-voltage side neutral point of the 220 kV transformer through a small reactance. This article analyzes the neutral point grounding situation of the main transformer in this zone and the equivalent network of the A substation. It also calculates the short-circuit capacity of the A substation and the single-phase short-circuit current when different main transformers are operated in parallel. The calculation shows that grounding the neutral point through a small reactance can reduce the single-phase short-circuit current and meet the requirements for equipment thermal stability. The article also proposes the operational and switching requirements when the neutral point small reactance is put into operation.