Research On The Characteristics Of Signal Line Coupling Strong Electromagnetic Pulse And Its Protective Measures

Aiming at the problem of conducted interference caused by the strong electromagnetic pulse coupled signal line,this paper builds a test platform to simulate the coupling characteristics of the signal line in the environment of lightning electromagnetic pulse and highaltitude nuclear electromagnetic pulse,and analyzes the overvoltage peak value,energy and spectrum distribution range that it is coupled to.Equal coupling law,and analyze and compare the coupling characteristics under different strong electromagnetic pulses.Combined with the cable coupling parameters and laws,a protection circuit combining a surge device and a filter circuit is designed for the video surveillance system.The design process of the protection circuit includes: firstly,the transient response test of the surge device;secondly,through the ADS simulation software designed a 9th-order Butterworth low-pass filter,and studied the influence of distributed capacitance on the insertion loss of the entire protection circuit;finally,the designed three-level protection circuit was tested for protection performance to verify its performance.The results of the test have certain practical significance for the research on strong electromagnetic pulse protection.The conclusions and research results obtained in this paper are as follows:(1)The voltage waveform coupled by the signal line near the simulated lightning channel is approximately a double exponential wave close to the source waveform,the rise time is at the ?s level,the frequency is mainly distributed in several kilohertz,and the coupling energy level is large;while the coupled nuclear electromagnetic pulse The voltage waveform of,which is a distinct damped oscillation waveform,has a rise time of ns level,a wider frequency distribution range,up to hundreds of megahertz,and the coupling energy is relatively small.(2)Analyze the transient response of different surge devices under nuclear electromagnetic pulse.As the injection current increases,the gas discharge tube and the varistor both increase the overshoot peak voltage and clamping voltage.The relationship between the pulse starting voltage and the injection current is the same,but the arc voltage is only related to the DC breakdown voltage.The greater the DC breakdown voltage,the greater the arc voltage.The response time of the three is in the ns level.The varistor is second,and the gas discharge tube is the slowest.(3)According to the working voltage of the protected circuit and the bandwidth of the working signal,the design index bandwidth of the filter is determined to be 0?10MHz,and the insertion loss is less than 3d B.The designed filter is added to the terminal of the signal line and placed in the bounded wave simulator to compare with the coupling voltage without the protection cable.After adding the filter,the coupling voltage is controlled at about 3V.(4)In order to study the influence of the distributed capacitance of TVS on its insertion loss,it is obtained through ADS simulation that the larger the distributed capacitance of the TVS tube,the greater the insertion loss of the entire protection circuit.Therefore,when choosing a TVS tube,try to choose the capacitance as much as possible.small.(5)Finally,the protection performance of the entire designed protection circuit is tested,and the final measured residual voltage and residual current basically meet the test standards.