| With the rapid development of the electronic information technology,more and more intelligent electrical and electronic devices are used in power systems.These devices are easily to be disturbed by the external intense electromagnetic pulse(EMP),which makes the protection against the intense EMP for power systems become a hotspot of electromagnetic compatibility study.As an important medium for energy distribution and information transmission in electrical and electronic equipment,cables are also a major coupling path of electromagnetic interference.The intense EMP usually generates coupling current on the cable through field-line coupling.The current can subsequently spread to the internal circuits of the connected device,thereby causing interference or even damage to sensitive devices,and bringing serious safety risks to the normal operation of the system.Therefore,it is necessary to study the coupling effect between the intense EMP and power systems.Considering that the actual power system is often situated in a large background area and complex environment,the characteristics of the intense EMP with a steep rise time and wide spectrum coverage make its propagation process more vulnerable to the undulating terrain and materials of the earth surface.At the same time,the disturbed cables,which may include different types,lengths,heights and terminal loads,etc,are widely distributed in the large area environment.Therefore,studying the coupling process between the intense EMP and cables existing in the large area environment is of great significance.However,neither the single experimental method nor the electromagnetic numerical method can directly solve this kind of complex problem involving the large area.Therefore,this dissertation systematically studies a variety of efficient time-domain hybrid algorithms,which are used to analyze the key problems in the coupling process between the intense EMP and cables with the large area environment considered.The main work of this dissertation is described as follows:1.A modified method for calculating the electromagnetic coupling of long cables near the ground is proposed.Firstly,for lumped excitation problem,based on the traditional FDTD method of transmission line equation,the time-domain pseudospectral solution technology is introduced.The proposed method divides the transmission line into non-uniform grids,which reduces 2 / 3 total grid,compared with the traditional FDTD method,and saves a lot of computing memory and time consumption.The proposed algorithm can effectively deal with the crosstalk problem of long cables.Secondly,for the external field excitation problem,a novel transmission line equation model of the overhead two-wire line is proposed.By considering the influence of the ground on the distributed parameters of the overhead two-wire line,the proposed algorithm is suitable for solving the coupling problem of the overhead two-wire line at any height.Moreover,compared with the traditional two wire model,the results are more accurate and the calculation efficiency is greatly improved.Finally,by combining the fast calculation method of lightning-induced field via the analytical method and the transmission line equation method,the coupling between the lightning electromagnetic pulse and the long-distance overhead line above the lossy ground is analyzed.2.An efficient time domain algorithm for the electromagnetic coupling of high overhead line is studied.Firstly,the thin wire method in 3D FDTD mesh is used to deal with the high overhead line.An improved processing method is proposed for the termination of the lumped element at the end of the transmission line.Through the interpolation technology,it can more accurately deal with the multi-element and multi position parallel loading problem in a unit cell.The method is also applied to the calculation of High-altitude Electromagnetic Pulse(HEMP)coupling of actual 35 k V overhead transmission line.By introducing STL adaptive mesh generation technology,the analysis of the shielded cavity is realized.An efficient time domain field-line hybrid method is proposed to improve the computational efficiency of the penetrative lines problem.The high overhead and vertical lines outside the shielded cavity are calculated by the thin-wire FDTD method,while the internal lines are solved by the transmission line equation method.The synchronous calculation of the hybrid method is realized by data exchange between field and line at the penetrative hole.Finally,the correctness and efficiency of the hybrid method are verified by several numerical examples,and the coupling analysis of the penetrative lines problem excited by a HEMP in the actual substation environment is also presented.3.A hybrid PE-TL method for the electromagnetic coupling calculation of wires in large area is proposed.Firstly,the two-way parabolic equation(TWPE)method is introduced to calculate the spatial electromagnetic field distribution in a large-scale and complex environment.The Split-Step Fourier Transform(SSFT)method is used to solve the equation,and the electromagnetic waves propagating forward and backward are grouped to improve the calculation efficiency.At the same time,considering the effect of terrain and obstacles,the step formula of the spatial field is obtained.The method is verified to be correct and applied to a factory environment with microwave source interference leakage,and the propagation and distribution of electromagnetic interference are calculated and evaluated.Then,using the advantages of the parabolic equation in calculating the wave propagation in a large-scale complex environment,and combining with the transmission line equation,a PE-TL hybrid method is proposed.In this method,TWPE is used to calculate the spatial field distribution in the large-area environment.The time-domain equivalent distributed sources on the wires are obtained by inverse Fourier transform and then substituted into the TL equation.One-dimensional FDTD is used to solve the equation to obtain the time-domain voltage and current response on the terminal load.The correctness and high efficiency of the hybrid method are verified by numerical examples in complex obstacle environment.Finally,the hybrid method is applied to the complex terrain environment in a large area and combined with digital map technology to quickly solve the response on the wire excited by a HEMP in real terrain environment.4.Aiming at the large area and multi-scale field-line coupling problem,an efficient time domain LAMS-TL hybrid method is proposed.Firstly,in order to deal with the complex circuit of cable termination and the problem of cable cascading,an efficient time domain field-circuit hybrid method is formed by using the Modified Nodal Analysis(MNA)method and the hybrid port model respectively.For improving the efficiency of FDTD in spatial field calculation,GPU computing technology based on CUDA is used to realize the parallel FDTD.Using parallel FDTD algorithm and transmission line equation method,the coupling effect of high-power microwave interference on actual box-type substation and internal cables is analyzed.Then,in order to improve the calculation efficiency and accuracy of multi-scale spatial electromagnetic field in a large area,PE and FDTD are combined.Spatial interpolation and time-frequency transformation technology are used to transfer PE calculation field to the connecting boundary surface of FDTD,while FDTD is used to complete the field-line coupling calculation of the fine target area.Based on the research content introduced in this study,a novel hybrid time-domain method for field-line coupling,namely LAMS-TL method,is proposed.The excitation field of the large-area cable and the target location complex cable network is provided by PE and FDTD,and different parts of the cable are connected as a whole by the cascade technology based on the hybrid port model,so as to realize the integrated calculation of the multi-scale field line coupling problem in the large area environment.Finally,this hybrid method is applied to the field-line coupling problem in a large-area complex environment.The HEMP coupling response on transmission line nodes of cables existing in the large area,complex substation and device scene is calculated. |
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