Investigation of a low frequency partial discharge location method utilising a 500 MW/23 kV turbo-generator stator

The development of a possible method for locating potentially dangerous partial discharges in large generator stator windings is described. The proposed location technique is based on spectral analyses of the low-frequency (0-30-kHz) components of the pulse waveshapes recorded at the line and neutral terminals of a phase. By taking the ratios of the spectra of the two signals and using appropriate digital processing methods it is shown how the procedures might form the basis of a practical system for locating unusual disturbances during high-voltage separate source tests on each phase and when operating under normal conditions with the neutral at, or near, each potential. The location parameters used in this method are independent of transit time measurements and are not affected by the 'capacitive' components of the pulses. The validity of the mathematical model and the location equations were investigated for injection of both sinusoidal voltages and simulated partial discharge pulses at various positions within a 500-MW, 23-kV generator stator winding. By application of computational procedures it was shown that the low-frequency data in the waveforms can be utilized for solving the equations to give location accuracies corresponding to better than one stator bar in 16 for the conditions tested.<
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