For long-length single-core submarine cables, it is crucial to ensure that the sheath overvoltage does not exceed the insulation level of the polyethylene corrosion-resistant sheath. To prevent excessive sheath overvoltage from the lead sheath from causing breakdown of the polyethylene corrosion-resistant sheath, the lead sheath and metal reinforcement strip must be grounded at regular intervals.
The design of grounding points and the calculation of distances between different points must be based on the specific conditions of the cable line. To ensure a watertight seal at the grounding point, grounding work is usually completed at the manufacturing plant. Generally, the grounding point is designed within the factory-installed flexible joint. Some foreign products use a polyethylene sheath with semiconductor electrodes, which avoids the hassle of grounding the sheath at a fixed point.
Factory-made flexible joints are a key feature of underwater cable systems. These joints are the same size as or slightly larger than the cable itself. Like all connected cables, they are flexible and can withstand various mechanical stresses such as tension, torsion, and bending. Therefore, factory-made flexible joints differ significantly in structure and performance from ordinary joints, but are very similar to the cable itself.
