As the outer diameter of the power cable is larger, transportation and laying are more difficult, and the power cable has stricter requirements for turning radius. In the construction of the power cable, if the turning angle is too large, the conductor may be mechanically damaged, and the mechanical damage cannot be seen because it is covered by the cable insulation layer. Even if the loop resistance, insulation and leakage tests are performed, it is difficult to find the defect. When it is overheated at the point of damage, the insulation strength of the cable decreases until failure occurs. The author has found that the reason for multiple cable head failures is that when the cable head is manufactured, the length of the three cable heads is the same, and due to the topography limitation when the device is connected, the medium phase cable head becomes long and arched, and the root of the cable head is damaged and discharged. After taking measures, according to the connection of different devices, the length of the connection of the intermediate phase cable heads should be appropriately shortened so that the three-phase cable heads are not subject to external forces. Practice has proved that the operation results are good. It can be seen that during the construction of the cable, the torsion to which the cable is subjected should be reduced as much as possible. When the cable is turned and the cable is left to stay, the cable is naturally bent and the phenomenon of internal mechanical damage is eliminated.