Analysis of Excitation Inrush Current and Secondary Harmonic during 500kV AC Field Commissioning Test of ±800kV Shan to Wu UHVDC

In the process of 500kV AC field commissioning test of ±800kV Shan to Wu UHVDC transmission project, the transformer in the station will be switched on and out over 5 times. As a result, the flux density in the iron core will increase greatly with the combined action of remanence and system voltage if transformer is switched on immediately after removal. Due to the saturation magnetization characteristics of the transformer iron core, the excitation reactance will be greatly reduced and the excitation current will be greatly increased, which is called excitation inrush current, 5-10 times that of the rated current. The inrush current is accompanied by a large amount of second harmonic, at the same time. Considering the new energy units of large capacity accessed in the vicinity of Wuhan converter station, theirs protection and control systems may cut off the units due to the second harmonic content of bus voltage and line current, leading to a large-scale off-grid of new energy units. In this paper, the transformer excitation inrush current, the secondary harmonic content and total harmonic distortion(herein after as THD) of 220kV bus voltage in the vicinity of Wuhan converter station are simulated and calculated, and several measures to prevent large-scale off-grid of new energy units are put forward at last.