Statistical Analysis of Energization Overvoltages in EHV Hybrid OHL–Cable Systems

Energization overvoltages are among the severest overvoltages stressing insulations of EHV power system components. Since these overvoltages have a statistical nature, the insulation level should be determined with the use of a statistical approach by which the distribution of overvoltages is calculated. Literature has properly studied the distribution of energization overvoltages in purely overhead line (OHL) or cable systems, but such a study is not available for hybrid systems consisting of both OHLs and cables. It is expected that the overvoltage distributions change substantially when both OHLs and cables are used in a transmission line. This paper tackles this issue by analyzing the overvoltage distributions due to the energization of a 380 kV hybrid OHL-cable circuit, in which the cable length is variable. The study includes various sensitivity analyses to find out the impact of system parameters and topology on overvoltages. By the statistical analysis, it has been discovered that energization overvoltages of a hybrid OHL-cable circuit are higher than those of a fully-cable circuit and very likely lower than those of a fully-OHL circuit with the same transmission lengths.