Design Of Uhf Antenna For Discharge Detection And Development Of Detection System

The occurrence of partial discharge is one of the main causes of power equipment failure,which will cause insulation damage and further deterioration.The off-line phenomenon of pantograph-catenary arc will affect the electromagnetic sensitive equipment in the railway signal system,and seriously affect the operation safety of the train.Therefore,it is an important method to prevent the occurrence of accidents and ensure the safe and stable operation of the system by monitoring the discharge to judge the insulation status and the contact state of pantograph and catenary.In order to achieve a high-performance monitoring system,a miniaturized,broadband and high-gain antenna needs to be designed.In this thesis,firstly,the design principle of Hilbert fractal antenna is studied,and the influence of wire width,peripheral dimension,dielectric layer thickness and feed point position on the performance of the antenna is simulated and analyzed.Then,a stacked fifth-order deformed Hilbert fractal antenna is designed.By increasing the order of fractal antenna to reduce the resonant frequencies,the antenna can be miniaturized.By introducing the stacked coupling structure,the antenna bandwidth was expanded.Through the deformation design of the connection mode,the gain of the antenna at each frequency point was further improved.The VSWR of the final antenna is less than 3.5(VSWR < 2 in the16～53MHz and 407～500MHz frequency bands),the normal gain is generally high and the directivity is good,and the gain at 0.1GHz is-38.1db.The research of the antenna provides a reference for the design of antenna sensor used in the detection of arc electromagnetic radiation signal of pantograph-catenary.The structure and working principle of the bowtie antenna were studied,and then based on the characteristics of electromagnetic waves excited by partial discharge of power equipment,a double-layer bowtie antenna with a metal back cavity was designed.By adjusting the structure of microstrip line to achieve the function of impedance transformation transition,the standing wave ratio of antenna was reduced.The size was reduced by bending the antenna radiation patch boundary,and the low-frequency bandwidth was effectively extended.Metal plates were added at the back,left and right sides to improve the directivity and gain of the antenna.The optimized antenna has a voltage standing wave ratio of less than 3 in the entire detection frequency band,where VSWR <2 in the frequency bands of0.3～0.82 GHz and 1.37～3 GHz.The antenna has good directivity and can well receive signals from the front.The minimum gain in the research band is-27 d B,in which the gain gradually increases with the increase of frequency in the 0.5 ～ 1.1GHz band,and then basically stabilizes between 1.1～3GHz,and the gain value is about 3d B.The antenna has good performance and can be used for UHF detection of partial discharge in power equipment.The research and selection of other signal processing devices of the discharge detection system is realized,including limiter,band-pass filter,amplifier and geophone.In cooperation with the antenna,a discharge detection system is preliminarily realized.The Labview program was designed to realize the functions of parameter setting and alarming,waveform display and analysis,data saving and historical data query,etc.Finally,each device was connected in sequence for preliminary discharge detection experiment.In the experiment,the amplitude of the discharge waveform obtained by Labview is about 1V,the waveform amplitude and pulse duration are consistent before and after detection,and the waveform displayed by Labview is basically the same as that obtained by high-speed digital oscilloscope,which preliminarily verifies the feasibility of the whole detection system.