Abstract: The neutral terminal or the phase terminal of the PT secondary should be earthed, and in the non-effective grounding system, the phase B terminal is usually connected to the earthing terminal. The different voltage between phase B earthing and phase N earthing system affects the protection function directly. This article uses the generator protection relay from NR Electric Co., Ltd as a sample and analyzes the impacts on each voltage element and protection function due to the change of the voltage when phase B is earthed. The analysis is purposed to provide some references when selecting a grounding method and protection function.