Study on 500 KV autotransformer with neutral point grounded through small reactance

With the fast development of power system and the expansion of the scale, 500kV grid structure is greatly enhanced, and 500kV autotransformer runs in the neutral grounding mode, 220kV single-phase grounding fault current may exceed three-phase grounding fault current which affects the security and stability of power grid operation. In this paper, we mainly study the current level of single-phase grounding fault on the 220kV side of the 500kV autotransformer, which is changed from the direct grounding to the series reactor. The equivalent model of 500kV system is built as an example, explaining the principle of 500kV autotransformer with neutral point grounded through small reactance that can limit 220kV single-phase grounding fault current, calculating different resistance reactance restriction results on the single-phase grounding fault current of 220kV side.