Mutual induction assessment in hybrid AC/DC transmission lines – A case Study

Converting one circuit of a double-circuit AC (Alternating Current) line to DC (Direct Current) is an attractive solution to increase the power transfer capacity of an existing electric corridor. One concern with such hybrid systems is the mutual electromagnetic induction between the two circuits, especially during asymmetric faults on the AC circuit when zero-sequence components arise. Previous works on the same topic do not focus on the analysis of harmonics produced by the interaction between the two systems. This paper presents the results obtained by a study of mutual interferences in a hybrid AC/DC transmission system during asymmetrical fault conditions. A hypothetical 400 kV AC - ±500 kV DC double-circuit line on the same tower is modelled in detail, and electromagnetic transient simulations have been performed using MATLAB/Simulink. The results highlight significant induced current components during faults, particularly if the AC circuit is not transposed.