Partial discharge location by cross-talk phenomena between three phase stator coils of generators

Online detecting PD of the stator insulation of generators is a good way to find some primary defects. But there are many kinds of pulse noises must be eliminated. In this paper, cross-talk phenomenon among the three phases of stator coils is described. A digital oscilloscope measured the signals coming from three high voltage buses of a real 50 MW generator. The coupling rule of PD pulse from one stator bar to another bar is analyzed. It is found that PD pulses can travel through the terminal part of stator coils by diffused capacitor between bar to bar. More closely the PD source is to the terminal bar where sensor is put on, more bigly the signal of this sensor is. From the amplitude of the output of the three sensors, the phase that the PD source belong to can be decided easily. Further more, the bar of PD source can be estimated by the decrease rule of PD pulse when it travels through the circle of the terminal part of stator coils.