Study On System For Ultrasonic Detection Of Generator Stator Winding Partial Discharge

Generator is extremely important electrical equipment in power systems. Generator failure is mainly caused by the insulation failure, which will also threaten the power system security and stability. By generator stator windings partial discharge (PD) on-line monitoring, the insulation condition of the generator stator can be judged, and the alarm can also be given to prevent accidents in advance, which will have great significance on stability, security and reliable operation of the entire power system.In the paper, on-line monitoring system of generator stator winding PD has been developed. The ultrasonic sensor has been used as system field-sensitive devices, which can gain ultrasonic signals generated by partial discharge.The ultrasonic signal is amplified, filtered, level lifted, A/D analog-digital convertered, and transfered by Universal Serial Bus(USB). The results are processed and analyzed, and then the characteristics of partial discharge have beeen extracted.The lower machine communication is programed by Keil C, including A/D converter of PD signal, the microcontroller initialization, the USB program. The relevant drivers and API functions are getten by USBXpress software and data communications between the USB and PC are realized.Based on virtual instrument technology and ultrasonic detection terminal, software system of generator stator windings PD ultrasonic testing is developed on the Lab VIEW platform. The software system realizes PD data receiving, decomposing and re-combining , and PD waveform is graphically displaied on human-computer interaction interface. The wavelet analysis software based on virtual instrument is developed and wavelet analysis of PD ultrasonic signal is done by the software. The database management of partial discharge is established to realize the database information inquiry.The propagation characteristics of PD ultrasonic from PD model and PD ultrasonic in generator stator winding are detected by using the detect system. Discharge sources in different position of the generator detected by the system are analyzed and compared. Propagation characteristic of ultrasonic signals in the generator stator is analysised.The system detects ultrasonic signals of generator stator bars successfully and PD ultrasonic signal is extracted by wavelet denoising method.Experimental results show that the proposed detection system is feasible and has high sensitivity and stability,which lay the foundations for further drawing the corresponding relationship between ultrasonic signals characteristics of PD and the insulation fault. With further improved, the system can detect operation state and failure point of the generator and realize planned inspection and maintenance, ensure that generators safely operate which will reduce the social economic losses effectively.