The Research Of Processing Signal And Location In On-line Partial Discharge Monitoring System For GIS

Higher and higher quality electrical power supply is needed with the development of the society. So gas insulated switchgear(GIS) has more and more applications in the power system due to its characteristics advantage, such as small volume, high quality, etc. Essentially, GIS is designed not to need maintenance. However in case of an insulation breakdown, it takes a longer time for its restoration and the breakdown causes more serious damage to system operation.As is known to all, partial discharge(PD) is a symptom of an insulation breakdown occurring in GIS. So it's very important to develop a new diagnostic technique to detect a characteristic symptom when PD occurring. At present, signals of light, supersonic wave, current and electromagnetic wave which are emitted from GIS can be utilized to determine whether PD occurs, however, the results are not satisfying due to the processing methods and the strong noise at the sites. To solve this problem, this paper proposes a noncontact detection method by using antennas fitted closely on the outer circumference of the insulation spacer to receive signals of electromagnetic wave emitted. The wavelet transform is used to filter the PD signal to get the signal with fewer disturbances. We emphasizes particularly on the research of using the time delay between signals from two antennas to locate the PD in GIS. Two methods, which are the unit impulse response method based on cross correlation and the energy ratio method based on examining the energy increasing of signals respectively, are employed to achieve the time delay estimation. The reason of affecting the estimation precision and the procedure for improvement are discussed. Experiments proved that the time delay between the signals can be use to find correctly the location of defects in GIS.This paper has three parts. The first part introduces basic knowledge such as PD's principle and detection methods used now whose shortcoming are also provided in brief. The second part introduces the system for detecting and our experiment, and the last part analyzes the data to locate the defects, discusses the results and gets the conclusion.