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Risks from ground fault transfer (GFT) on closed-loop high-voltage (HV) underground distribution systems (UGDS) with cables running in a common route are assessed based on simulations by the Alternative Transienta Program (ATP) of the Electromagnetic Transients Program. To model the system, the configuration of a real and typical closed-loop HV UGDS is explicitly depicted. The complex connecting relationships between cable metallic shields, grounding electrodes, parallel ground continuity conductors (PGCCs), and surge suppressors at manholes and substations are clearly shown. Then, through the system modeling and simulation by ATP, the GFT characteristics (i.e., the distributions of currents and potentials on cable metallic shields and PGCCs along the cable length are analyzed). Based on the simulation results, the risks from GFT on personnel, equipment, devices, or other associated systems are assessed. Finally, the damages caused by a three-phase ground fault in a customer substation are surveyed to certify assessment result of risks and the severity of GFT on closed-loop HV UGDS with cables running in a common route.