Failure Mechanism Analysis of Busbar of MMC Submodule Under DC Fault

Overcurrent induced by DC fault may cause great electromagnetic force and temperature rise on the busbar of modular multilevel converter (MMC) submodule, which may result in permanent failure of the busbar. In order to explore the failure mechanism of the busbar under DC fault, we analyzed the electromagnetic-temperature-mechanical coupling field of the busbar based on DC fault calculation and multiphysical field simulation. First of all, based on the arm equivalent model, we accurately calculated the arm fault current, analyzed the influence of fault time on the arm fault current, and obtained the most serious fault current magnitude that may occur on the submodule busbar. Secondly, the electromagnetic force and Joule heat of each part submodule busbar were modeled, and the temperature rise and stress distribution of each part of busbar were solved. The calculation results show that the temperature rise of the busbar is negligible, but the mechanical stress is large, the deformation is serious, and the axial force on the bypass thyristor bolts is the largest of all, which may cause bolt detachment failure. This paper provides useful information for MMC submodule busbar failure analysis and design. © 2020, High Voltage Engineering Editorial Department of CEPRI. All right reserved.