The high-voltage and large-capacity DC transformer is the core equipment supporting large-scale renewable energy transmission. As a forward-looking solution for high-capacity high-voltage DC transformers

the high-voltage DC transformer with arm multiplexing presents a significant technical challenge in revealing its fault characteristics' evolution. To address the issues such as short transient duration of internal branch faults

limited electrical features

and complex coupling paths

this paper establishes an equivalent circuit model for branch short-circuit faults with AC/DC decoupling and derives the analytical expressions for physical quantities from the fault occurrence to submodule locking. The fault characteristics of branch short-circuit faults are revealed. A comparison is made between the equivalent model and the switch model of the high-voltage DC transformer with arm multiplexing which is built on the basis of MATLAB/Simulink. Simulation results show that the proposed fault analysis method

considering the interaction coupling effects of internal branch faults

reflects the fault evolution of branch short-circuits in the high-voltage DC transformer with arm multiplexing

providing references for subsequent fault feature extraction

accurate fault identification

and rapid protection techniques.