Based on the sequential component method

the inter-line fault of mixed-voltage double-circuit lines partly on the same tower in neutral point directly grounding and indirectly grounding systems near substations is studied.Firstly

the zero-sequence mutual inductance between mixed-voltage double-circuit lines partly on same tower is eliminated

and the system is decoupled into comprehensive positive-

negative-and zero-sequence networks. According to wiring mode of three-winding transformers

the amplitude and phase angle of common impedance parts of the comprehensive positive-

negative-and zero-sequence networks are corrected

and the independent six-sequence network of mixed-voltage double-circuit lines partly on the same tower under different grounding modes of neutral points is obtained. The boundary condition of fault point is listed according to the fault types

and the short circuit current at fault point is obtained by the composite sequence network and its solution equations. Different types of faults in mixed-voltage（220 k V/110 kV/35 k V） double-circuit lines partly on same tower in neutral point directly grounded and indirectly grounded systems are simulated with PSCAD software

and the simulative results verify the accuracy and practicability of the proposed method.