Stator ground fault protection based on phase angle differential of delta third harmonic voltages

New stator ground fault protection principle is presented in this paper, which takes into account the phase angle comparison of the third-harmonic voltages at the generator terminals and the neutral. Analysis results show that the phase angle differential value of Δ-third-harmonic voltages under normal condition and fault condition will present greatly different, and this characteristic could not be influenced by the operation conditions. Thus, it can be used to detect the generator stator ground fault, which could ensure higher sensitivity because of cancellation of the pre-fault component. The start-up component is based on the wavelet transform (WT), its effects are also described. Experimental and field test results demonstrate that new scheme can obtain high sensitivity and reliability the generator relay required during different operation conditions.