Simulating Calculations of Transient Voltages and Insulation Coordination on 500 kV AC XLPE Submarine Cable Line

A power transmission line with a 500 kV AC cross linked polyethylene (XLPE) submarine cable combined with the overhead lines will be built at Zhoushan of China in 2018. The calculation of various transient voltages on the insulation and insulating sheath of the submarine cables is one of important subjects. This paper aims to clarify the characteristics of transient voltages under various fault conditions for ensuring its safety and reliability. The models of simulating calculation for the whole transmission system, including of overhead lines and substations, were established with the PSCAD/EMTDC software to analyze the characteristics and distributions of various transient voltages on the main insulation and insulating sheath along a near 17 km submarine cable. The results indicated the highest switching transient overvoltage on the insulation of cable would occur when switching off an un-loaded cable line with a concomitant re-striking of circuit breaker, and could reach 850kV (or 1.90 p.u.). The highest transient voltages on the insulation sheath tended to locate near the middle of the long-distance submarine cables, and would reach 11.4kV. The insulation margin of submarine cable insulation was over 20 percent under the maximum switching or lightning transient overvoltage, and the one of the insulating sheath exceeded at least 90 percent based on their practically measured withstand voltages.