IFRA Technique to Detect Stator Winding High Impedance Earth Faults During Startup in Salient-Pole Synchronous Generators

This article introduces an impulse frequency response analysis (IFRA) technique to detect stator winding earth faults in salient-pole synchronous generators during startup. The proposed technique involves injecting a square pulse with an appropriate frequency spectrum into the neutral point of the stator winding, which is grounded through a resistance. The transmitted signals from the three phases are captured through high-pass filters installed at the machine terminals. These signals are decomposed in the time-frequency domain using the stationary wavelet transform (SWT). By analyzing and comparing the similarity/dissimilarity of these signals at an appropriate frequency band, a numerical index is defined to detect earth faults. Experimental results on a laboratory salient-pole synchronous generator demonstrate that this technique can detect high-impedance earth faults, even in the vicinity of the neutral point, with high sensitivity. Additionally, the defective phase can be identified using this method.