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The insulation level of power apparatus is mainly determined by the amplitudes and waveforms of system overvoltages. The substation is handled as a lumped equivalent model, and the detailed substation structure is not taken into account in present switching transient calculations. In this study, the influence of considering a substation structure on the switching transient calculation of a 1000-kV ultra-high-voltage system is analyzed, and the factors affecting this calculation are obtained. Generally, considering the substation structure will not affect the calculation of switching overvoltage amplitudes, but it will generate a damped oscillation with a very sharp wavefront and very high frequencies upon the familiar switching transient waveform. Attention should be paid to the insulation withstand level of air gaps and power apparatus to this kind of complex wave of a short-front rapid impulse superimposed on a long-front slow impulse.