| The coupled protection of strong electromagnetic pulse in power system has become a research hotspot.In this paper,the transmission cable,an important transmission medium in power system,is studied in detail.Based on the basic transmission line theory,this paper solves the coupling response problem of transmission line models under different conditions when the transmission line is coupled with HEMP,and combines the practice with the theory by direct experiment.Finally,a design idea of protection circuit for power transmission cable coupled with strong electromagnetic pulse is provided,and its validity is verified by simulation and test.Specific work has been carried out as follows:Firstly,the basic overview of HEMP is given.The field-line coupling model is used to solve the relevant equations of current and voltage.A single transmission cable is tested by using a bounded wave HEMP simulator.The coupling wave is a typical damped oscillating wave,which has a positive correlation with the electric field strength and the energy is concentrated within 100 MHz.At the same time,the coupling effect of transmission cable will change with different erection height,incident elevation,cross-section area,coupling length and terminal load.Then,the coupling effect of multiple transmission cables is explored.The excitation source equation is analyzed by the field-line coupling model,and several arrangement modes are tested.It is found that the shielding effect of multiple transmission cables is smaller than that of a single transmission cable,and the voltage and energy coupled to a regular triangle arrangement is smaller than that of a single transmission cable.Therefore,it is assumed that the shielding effect would be better if a positive N-sided arrangement was used.Regardless of the arrangement,the voltage and energy coupled by the transmission cable will increase with the distance between each cable,that is,the shielding effect will be weakened with the increase of the spacing.These coupling characteristics have some reference value for the way we place transmission cables in our real life.Finally,the transient response tests of three different types of surge protection devices are carried out.Varistor and gas discharge tube are selected as transient protection devices of protection circuit according to their transient response characteristics.A seven-order Butterworth low-pass filter with a cutoff frequency of 100 k Hz is designed according to its characteristics,which meets the design requirements of the low-pass filter as a whole.After three-stage protection is combined,the coupling test is carried out,and the coupling voltage and damped oscillation frequency are obviously suppressed,which has significant protection effect.The test is carried out through the method of Military Standard,reaching the A-level inhibition level. |
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