Experimental Study on Overvoltage Propagation Characteristics of High-Voltage Submarine Cables

With the large-scale development of deep-sea offshore wind power, the insulation safety of high-voltage submarine cable outer sheaths faces severe challenges, yet the propagation characteristics and coupling mechanisms of cable-core overvoltages to the metal sheath remain unclear. To address this, a physical experimental platform was established for lightning impulse testing based on a 66 kV submarine cable, and the transient potential response characteristics of the metal sheath under various operating conditions were systematically investigated. The results indicate that under fully suspended conditions, the sheath voltage is primarily determined by the voltage division caused by the radial coaxial distributed capacitance. When a 30.6 kV lightning impulse voltage is applied, the overall potential of the sheath approaches that of the cable core; under conditions where the sheath is grounded at the end, the capacitively coupled charge is rapidly discharged, and the transient potential is then dominated by inductive coupling, with its variation strictly corresponding to the rate of change in the cable-core’s transient current; under conditions where the sheath is fully suspended and the cable core is grounded, the potential of the metal sheath exhibits a dynamic superposition of the radial capacitive common-mode voltage and the axial inductive differential-mode potential difference. These findings demonstrate that metallic-sheath grounding conditions significantly influence the relative contributions of capacitive and inductive coupling to transient sheath overvoltages under lightning impulse excitation. The experimental results provide a physical basis for further investigation of sheath grounding arrangements and overvoltage protection strategies.