Abstract: One Nuclear Power Station No. 3 Unit reconstruction project has improved the transformer design due to No. 1&2 Units had ever suffered failures of the interconnecting transformer coil by VFTO, so the new No.3 interconnecting transformer should be fully considered the impact of VFTO to avoid the similar incidents. This article analyzed 10 routine operations about the VFTO impact to the equipment by using the ATP electromagnetic transient calculation program. The results shown that the overvoltage value near isolating switch is the highest, which is 2.95 p.u., the maximum overvoltage at the transformer entrance is 1.60 p.u., the insulation level of the equipment could fulfill the requirement of VFTO.