Research On Head Wave Characteristics Of UHF Partial Discharge Signal And Its Influencing Factors

The long-term effective and safe operation of many electrical equipment in substations plays a vital role in the stable development of the national economy.When using UHF method to detect electrical equipment,accurate judgment of the arrival time of UHF signal head wave is the decisive factor to improve the detection effect of partial discharge.But after the UHF signal passes through the complex radiation path and the sensor system,the waveform will be seriously distorted,which will weaken the reading effect of the head wave.Therefore,it is urgent to study the characteristics of the original UHF signal,the characteristics of the sensor system and the influence of the propagation path on the UHF head wave,so as to provide technical reference for improving the detection effect of partial discharge.In order to study the characteristics of the first wave of the original UHF signal,this paper first introduces the simulation software and experimental platform for the research;establishes the free space model and the bowtie antenna simulation model,and builds the pressurization device,the test cavity,the current pulse and the special A test platform consisting of a high-frequency signal acquisition loop.The electric field first wave excited by the current source and the relationship between the output voltage of the antenna and the electric field around the antenna are analyzed.The original current pulses with different defects in free space are collected,and the characteristics of the simulated and measured UHF signals are compared.The antenna input impedance is analyzed for UHF.The influence of the signal waveform;the influence of the detection frequency band on the amplitude of the first wave of UHF signal is analyzed by software filtering,and the ability of different types of antennas to induce the first wave of UHF signal is compared.The research shows that the antenna output voltage is the integral of the electric field on the effective length of the antenna,that is,the antenna voltage waveform is similar to the electric field waveform.The first wave of the output voltage corresponds to the rising edge of the pulse current source;the non-resistive part of the input impedance causes the signal first wave.Decrease,waveform oscillation;increase the filter upper limit cutoff frequency is less than reduce the filter lower limit cutoff frequency to the first wave;the first wave amplitude of the horn antenna output voltage is larger than the large bow tie antenna and the small bow tie antenna,but the small bow tie The first amplitude of the antenna is closer to the maximum amplitude of the UHF waveform.For the sake of researching the influence of propagation path on UHF head wave,the characteristics of which during electromagnetic wave radiation are analyzed through simulation and experiment in the winding of smoothing reactor,the tank of transformer elevator,and the GIS cavity.It is found that the UHF head wave amplitude of horizontal sensor of smoothing reactor is larger than that of oblique sensor and the first wave amplitude of sensor below reactor.After UHF signal radiates outward through the outer oil passage of the casing,the head wave amplitude attenuates about 44 dB.For defect detection in the oil tank at the bottom of the casing,a low frequency acquisition system should be selected to obtain a larger first wave.When electromagnetic wave propagates in the GIS cavity,the amplitude of UHF first wave passing through the basin insulator attenuates about twice as much as that of UHF first wave passing through the basin insulator.In summary,this paper simulates and analyses the output voltage head wave of antenna,compares and analyses the influence of different defects,different detection bands and different propagation paths on UHF head wave in free space,and proposes different detection methods for different equipment.