Highspeed rail longdistance power lines have gradually realized full cable,and some highspeed rail power systems still use neutral point ungrounding. Therefore,when the system is singlephase grounded,it is often accompanied by intermittent arc grounding,which causes damage to some PTs. In order to solve the PT damage phenomenon of long cable line,the main reason of the PT burnout of highspeed long cable line is obtained through theoretical analysis without changing the grounding mode and line structure of the neutral point. Then,by constructing the simulation model,the railway is pointed out. In the longdistance cable line,the neutral point ungrounded system should be designed according to the ungrounded system for electrical equipment selection and insulation coordination. The electromagnetic PT with higher excitation point saturation should be selected. The PT rated voltage factor should be greater than 2.2 pu;The scheme is applied to a number of highlength cablelength cable distribution stations in Wuxi East,and good results have been obtained,which verifies the feasibility of the scheme.