| The numerical methods to predict the transient electromagnetic environments when the circuit breakers and disconnect switches are operated in air-insulated substations are researched in this paper .The main contents are as follows:(1)The electromagnetic environments and interference sources in the air-insulated substations are described .The basic concepts of electromagnetic topology are described .And an electromagnetic topological shielding diagram of a small shielding room in the air-insulated substation is made.(2) As the foundation of the multi-conductor transmission line theory, the transmission line theory is introduced. Then, the models and equations of the multi-conductor transmission line are introduced in detail . The finite difference-time domain method for the multi-conductor transmission lines with many branches is proposed , and the interative equations of the connection points are analyzed.(3) After a model of bus-bars in a 500kV substation is set up, the transient voltage and current are predicted, using FDTD method.(4)The paper researches the interference on the ports of the secondary cables, which are caused by the transient voltages and currents on the high voltage bus via the instrument transformers. In view of this impact, the shielding cable grounding modes are discussed. The protective measures against transient electromagnetic interference caused by switching operation are proposed. |
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