| In power system,the detection of corona discharge in overhead lines can find the occurrence of corona discharge in time,effectively eliminate the hidden danger,and avoid more serious accidents.The primary causes of corona discharge in overhead lines are poor contact between transmission lines and metal fittings of insulators,contamination on insulator surface,aging insulators,and strand breakage of lines.The occurrence of corona discharge will bring power consumption of overhead lines,interference of frequency modulation(FM)broadcasting signal,and rising of the local temperature of transmission equipment.In addition,the discharge itself will produce corrosive gases,such as ozone and nitrogen oxides,which will aggravate the aging of insulator and other equipment,and may cause serious lines fault.If it can be detected and eliminated in time,it is of great significance.In this paper,the time-frequency distribution characteristics of radio-frequency(RF)electromagnetic wave of corona discharge are studied by using electromagnetic wave measurement method.According to the spectrum distribution of corona discharge,the corresponding RF detection antenna and hardware circuit are designed.In order to realize the short-distance detection of overhead lines with the detection device installed on the unmanned aerial vehicle(UAV),the shell is designed and the RF detection device is completed.Through the field test of overhead lines,the function of discharge detection of the detection device is verified.The main works of this paper are as follows:(1)The detection frequency range of RF electromagnetic wave of corona discharge is studied.A simulated test platform of corona discharge is established to analyze the time and frequency distribution of RF electromagnetic wave signals generated by corona discharge.The main frequency distribution of RF electromagnetic wave signal of corona discharge is determined.Through the analysis of the noise signal near the outdoor overhead line,the main frequency range of the interference noise is determined,so that the detection frequency range of RF electromagnetic wave of corona discharge is100MHz～500MHz.(2)The detection antenna of RF electromagnetic wave of corona discharge is studied.According to the detection frequency range of RF electromagnetic wave of corona discharge and the space limitation of UAV,the antenna is required to be able to realize the detection frequency band of corona discharge and small size.The rectangular spiral antenna and Hilbert fractal antenna are selected as the main research objects,and the structural characteristics of the two antennas are simulated and analyzed.By combining the characteristics of the two antenna structures,an innovative antenna structure of rectangular spiral with a Hilbert unit(RSHU)is proposed,and the antenna design is completed through simulation optimization.The final antenna size is 100 mm× 100 mm × 1.6 mm.The real antenna is 35 g,and the detection function of RSHU antenna is verified by discharge test.(3)The detection hardware circuit of detection device of corona discharge is designed.The hardware circuit is divided into LNA,filtering,VGA amplification,envelope detection,signal processing,post amplification,storage,Wi Fi communication,power supply and other parts.The circuit schematic diagram is designed and the hardware circuit is completed.According to the available space under the UAV,the size of the RF detection antenna and the occupied space of the hardware circuit,the RF detection device shell which can be installed in the UAV is designed.(4)The field test of corona discharge in overhead lines.A set of RF electromagnetic wave detection device for detecting corona discharge in overhead lines is formed by assembling and debugging the RF detection antenna,hardware circuit and device shell.In order to illustrate that the detection device can achieve corona discharge detection,it is brought into the 500 k V overhead lines for experimental analysis of field test.The UAV was used to test the insulator fittings on the left,right and jump string parts of the overhead line tower.The discharge signals of different parts were measured successfully,and the relative strength of the discharge can be distinguished.The experimental results showed that the RF detection device can be carried by UAV and used for close-range discharge detection,which provides a new and convenient detection method for corona discharge detection of overhead lines. |
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