Frequency Characteristics Analysis of Partial Discharge Ultrasonic Signals in Generator Stator Windings

In recent years, due to the uneven distribution of electric field at the end of stator winding, ventilation slot and slot gap, stator rod insulation corrosion breakdown accidents often occur, which seriously affects the normal operation of generator and the stability of power grid. Due to the narrow space inside the generator, it is impossible to realize the internal installation of the traditional piezoelectric ceramic ultrasonic sensor, so it is proposed to implant the sensor into the notch block between the stator winding of the generator to achieve accurate detection. The research is divided into two steps, firstly, the time-frequency characteristics of the stator winding partial discharge ultrasonic signal are studied, and secondly, the design of the implantable ultrasonic sensor is carried out on the basis of the previous step. This paper is the first step of the study. The partial discharge experiment of stator winding slot of large generator is carried out. The ultrasonic signal generated during partial discharge is measured and the frequency characteristic of the ultrasonic signal is analyzed. The results show that when the insulation structure of the stator winding of the generator is not damaged obviously, the winding has internal discharge, and the characteristic frequency of the ultrasonic signal is 80kHz100kHz. When the low-resistance anti-corona layer is damaged, the ultrasonic signal frequency generated by the corona discharge at the notch is 20kHz-50kHz, and the signal will be superimposed with the 80kHz-100kHz high-frequency signal generated by the internal structure discharge of the winding. The research in this paper provides a practical basis for the diagnosis of generator stator winding insulation state based on partial discharge ultrasonic signal analysis.