Tri-axial cable has been intensively developed recently by the advantages of their reduced amount of HTS tapes, small leakage field, and low heat loss as compared with HTS Coaxial cable. Before the cable can be installed in power grid, the reliability of the cable in steady-state operation and any dynamics condition should be ensuring. However, in steady-state operation, the differences in radius due to concentric phase structures induce an inherent imbalance in the three-phase currents distribution. In our previous research, a Tri-axial cable composed of two longitudinal sections with different twist pitches was proposed. A symmetrical inductance distribution in three phases was acquired by adjusting pitches. In this paper, for a long transmission line, the electric circuit PI model, which treats an unbalanced phase distribution due to unsymmetrical capacitance in the Tri-axial structure, should be used for analysis. A simulation of typical power capacity Tri-axial cables was carried out to analyze the effect of unsymmetrical capacitance. Meantime, in dynamics condition, simulation of single line to ground fault was carried out in the cable with different combinations of radius and stabilizer area design to observe the temperature rise.
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