Baotou Power Supply Bureau Lugang Substation has two main transformers,in operation with one transformer′s neutral point grounding directly both in 220 kV side and 110 kV side,the other one′s type is gap grounding.When system is fault,grounding transformer tripping and system losing ground,high zero-sequence over-voltage appeared.Put forward the method for both transformer′s 220 kV and 110 kV neutral points grounding directly.After implementation,when the earthed transformer tripped while system is fault,th...