As the connection unit of the flexible HVDC transmission project

the insulation level of the HVDC submarine cable is critical to the safe operation of project. The statistical method is applied to calculate the overvoltage distribution of flexible HVDC submarine cables based on the modular multilevel converter in this work. The flexible HVDC submarine cables are studied to get the insulation level of the cables

which connect Dinghai Convertor Station and Daishan Convertor Station in Zhoushan multiterminal flexible HVDC project. The maximum fault overvoltage is obtained by simulating calculation

which is 403.44 k V between conductor and lead sheath

6.72 k V between lead sheath and armor

and 0.39 k V between armor and ground. The insulation level of the cables is determined by the insulation with 30% margin

which is 525 k V between conductor and lead sheath

9 k V between lead sheath and armor

and 0.6 k V between armor and ground. The results can provide the references for the selection and test of the flexible HVDC cables.