Study On Partial Disrcharge Signals Of Air-insulated Substation Monitoring Based On Ultral High Frequency Method

Partial discharge(PD)not only threatens safety of electrical equipments, but also is an indicator of insulation integrity degeneration, so research on PD of electrical equipments detection and diagnosis has important scientific significance and extensive useful value. For safety of substation operation, PD level of all the high-voltage equipments within substation should be monitored, the previous research was always applied to detect internal PD of solo electrical equipment, but the cost of monitoring all the equipments within substation by providing the specialized monitoring system to electrical equipments and attachments with relative unimportance and low price is too high. Therefore, this paper has researched the approach on monitoring PD signals within air-insulated substation by fixed antenna array based on ultra-high frequency(UHF)method,electromagnetic theory,electrical measurement,microwave and antenna theory, this approach is mainly used to monitor external insulations and attachments of electrical equipments, can monitor the substation for a long time and sample UHF signals in substation to analysis and calculate, sensors installation and detection are not contact with equipments, safety of substation can be enhanced by combining this approach with internal PD of electrical equipments monitoring approach. Research content of this paper as follows:The principle of UHF based PD within air-insulated substation monitoring by fixed antenna array and the mechanism of PD electromagnetic wave which propagate in the space of air-insulated substation have been researched. First, the principle, approach and applied range of UHF based PD signals within air-insulated substation monitoring by fixed antenna array has been introduced, and then PD electromagnetic wave attenuation and delay while propagating in space of substation has been researched at the angle of UHF electromagnetic wave propagation, the main reasons of PD signals attenuation and delay have been analysed, the approach for decreasing PD signals attenuation and delay as far as possible has been discussed.A discone antenna used to detect PD signals in the air of air-insulated substation has been developed. First, discone antenna has been analyzed and calculated and relation between antenna geometry and performance has been found by simulation, geometry of discone antenna used to detect PD signals within air-insulated substation has been optimized according to summarizing approach of designing discone antenna. Then, discone antenna with cone angle 25°, cone height 30cm, disk radius 20cm has been discrete made, this antenna has advantage with small volume, low weight, easy installation and detachability. This antenna has impedance bandwidth 200MHz to above 2GHz in which antenna VSWR is less than 2, average gain above 4dB, most gain direction in E plane pattern is below the antenna according to measurement, otherwise, this antenna has good performance in UHF signals receiving test.Test research of UHF based PD within air-insulated substation monitoring by fixed antenna array has been carried on. In the outdoor field test, signals arriving time delays of antenna array is almost the same with theoretic time delays, and accuracy of estimating time delays is very important to locate discharge source exactly. In one 220kV air-insulated substation test, discharge signals far away from 35m horizontally have been detected by 4 antenna array installed on the roof of control room and energy frequency spectrum of the signals is mainly below 350MHz, the discharge source has been calculated accurately via detecting discharge signals, discharge source is isolating switch with air-insulation discharge through checking, so this approach has been proved to be feasible and valid in engineering application.