There is zero sequence mutual inductance between the double-circuit lines on the same tower without parallel operation when an asymmetric grounding fault occurred in single line

which should be considered in line fault calculation. In this paper

the zero sequence decoupling model of loose coupling transformer is proposed

based on which

zero sequence network of not parallel operation with parallel circuits on the same tower is decoupled to obtain the line equivalent circuit. Then the equivalent zero sequence impedance of the line is obtained. In the fault analysis of not parallel operation with double-circuit lines on the same tower

the traditional symmetrical component method is employed to calculate the sequence current where the fault is with the line sequence resistance obtained. And then the phase currents can be obtained

thereby completing the calculation of the single line fault. The zero sequence decoupling model proposed is verified by the result of PSCAD/EMTDC.