| With the increase of voltage level and the more decentralization of secondary equipment, the secondary circuit of substation is in a strong electromagnetic environment. Because of the_secondary circuit in DC system being interfered, there are many trip accidents happened in power grid without any fault in recent years. This phenomenon has caused a serious threat to power grid and affected the safety and the reliability of power system. It is of great theoretical significance and practical value to research the electromagnetic coupling of the transient electromagnetic field to secondary cable in substations.In this thesis the multi-conductor transmission line based on the finite difference time domain method and electromagnetic interference coupling secondary cable in substation are emphatically researched. Firstly, from the conception of electromagnetic compatibility, the main interference in substation is classified, According to the object of study——the different channel and mechanism of interference of second cable, mode of interference coupling to secondary cable is classified into three kinds:conductive coupling,radiative coupling and secondary circuit itself coupling. The application of FDTD method in multi-conductor transmission line model is emphatically researched, the affectting discipline of the FDTD method in different connected transmission line is discussed. Then, the three most serious electromagnetic interference of secondary cable is modeled and simulation calculation in substation. Lastly, do many testing to cable in laboratory to get the finite difference time domain method's availability validation and experiment results' comparison. The result will provide a certain reference value to the protection of the secondary cable in substation.
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