| The transmission line has been widely used in diverse fields of modern society,especial in the power and communication system. However, in some serious electromagnetic environment, such as nuclear explosion, lightning electromagnetic wave and ultra-wide LEMP, transmission line could inevitably couple the energy into the system.LEMP occurs most frequently,resulting the most extensive hazards and causing the largest loss of property. Due to the layout characteristics, the transmission line is very easy to become a coupling medium, whose coupling method includes the radiation coupling and induction coupling.The coupling over-voltage and current cause damage to the whole system. The signal cable is more sensitive to the over-voltage because of the numerous back-end electronic components,so it is vulnerable to be influenced by the lightning current.Therefore, it is necessary to study the characteristics of electromagnetic compatibility of the transmission line under the lightning electromagnetic environment. At the same time, the research on signal SPD can ensure the normal operation of the signal transmission and also solve the treats of lightning over-voltage. This paper consists of three parts, firstly, the characteristic of single-double line scanning and coupling lightning electromagnetic wave has been analyzed by the simulated 8/20?s combined waveform, then the variation of coupling voltage is obtained. Secondly, the transient performance of TVS has been studied by utilizing the simulated 8/20?s combined waveform and damped oscillatory wave. Thirdly, the transient performance of unbalanced signal has been discussed. Draw a conclusion:1.The transmission line is selective to the frequency of coupling LEMP, the energy mainly gathers in the extreme low frequency. By contrary, the coupling wave has shorter time period and steeper waveform form time domain. Changing the coupling area of the cable would directly affect the voltage amplitude. The voltage is linear with the length and height of the cable, and the testing results are consistent with the theory. During the test, the impedance mutation would cause high frequency mode.2.After the conducting caused by the 8/20?s and damping oscillations waveform, the residual voltage and current would increase with the rising impact voltage, and its absorbed energy reaches its maximum in deep saturation zone.When the TVS is broken, it cannot absorb the energy efficiently, so the residual voltage decreases rapidly. With the increase of the TVS's nominal clamping voltage,the current decreases. The characteristics of TVS is not only related to the voltage amplitude and also the energy.3.For signal SPD, the higher the frequency is, the more severe the attenuation is.Choosing the most suitable TVS could decrease the affection caused by SPD network. Meanwhile, the decoupling resistance of signal SPD is generally from 2.2? to 10?and should be taken according to the structure and characteristic of the appropriate decoupling resistance. The residual voltage of unbalanced signal increases with the impulse voltage, and the higher the operating voltage the TVS is,the higher the residual voltage is. When the GDT is not in operation, SPD clamps relying on TVS and the current is small. When the over-voltage beyond the threshold and make the GDT work, the current increases rapidly with the impulse voltage. From the data analysis, the discharge ratio of GDT and TVS is about 9:1. |
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