To make up the defect of 100% stator grounding protection function， the protection scheme based on injecting 20 Hz electric source signal is proposed. The grounding resistance setting value is constant for the traditional stator grounding protection scheme of injecting 20 Hz electric source signal. The setting value is not varied when protection equipment operates. This paper discusses the existing questions of the traditional scheme， and proposes a new self adaptive scheme. The new scheme can self-adaptively adjust the setting value of grounding resistance according to the different operation conditions， grounding position and the grounding current limiting value. It can react quickly if the grounding current is greater than the limiting current in spite of the grounding position. The new scheme is more secure and flexible.