| Gas-insulated switchgear(GIS) was widely used in ultrahigh voltage transformation system in cities. Partial discharge (PD) was not only a symbol and representation of the degradation of insulation, but also led to further deterioration. In order to improve the reliability of GIS, a large amount of research had been studied both in China and abroad, and the ultrasonic method was proved to be highly serviceable in PD detection. However, the numerical simulation of the PD signal was very few, and the characteristics of the PD signal were mostly experimental results. Therefore, in view of this problem, the finite difference time domain method was used to simulate the propagation characteristics of ultrasonic signals in GIS.The research of GIS partial discharge propagation of ultrasonic signals could provide a theoretical reference for PD location calculation. Paper main research contents and results are as follows:(l)Mechanism for ultrasonic signals generated by PD based on the electromagnetics-mechanics-acoustics theory was described. The main factors affecting the detection sensitivity of ultrasonic sensors was analyzed.Besides,the relationship between the thickness and the resonant frequency of the piezoelectric crystal was studied.(2)The FDTD method was used to discrete the acoustic wave equation., and an ultrasonic signals propagation model was established based on HOkV GIS.The attenuation characteristics of ultrasonic signal in GIS, catadioptric problem, sound pressure distribution of PD source location, and the angle detection were studied.The results showed that the amplitude of ultrasonic signal was inversely proportional to the propagation distance,the serious interfacial loss occurred in the gas solid interface and metal guide bar had a serious effect on the propagation of ultrasonic signals.Besides,the bottom of GIS was a suitable detction location.(3)The design of detction system, this part mainly includes two parts of software and hardware. The hardware part includes the selection of emission sensor based on the characteristics of Ultrasonic Signals in GIS, and the design of the corresponding pre amplifier filter circuit was designed. The data acquisition and transmission module based on FPGA chip was desgned. At last,a slave computer software was wrote using SOPC and NiosII for the Control strategy of data acquisition and transmission.Finally, the PD detection system was tested in 110kV GIS. The result showed the effectiveness of the system. |
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