Structure Optimization for Downlead Cable of 110 kV Insulated Optical-Unit Phase Conductor

Abstract Currently, the structure of insulated optical-unit phase conductor (IOPPC) is gradually being employed in 10 kV and 110 kV power transmission lines, replacing the existing Optical Fiber Composition Phase Conductor (OPPC) structures. However, incidents of lines breakage have occurred in the widespread application of IOPPC downlead cables in 110 kV lines. Addressing these breakage incidents, this paper proposes a modified structure for the IOPPC downlead cable. Initially, finite element method is employed to calculate the electric field intensity of both the traditional and modified IOPPC downlead cable structures under a 110 kV voltage, providing preliminary validation of the effectiveness of the proposed modification. Subsequently, power frequency withstand tests are conducted to further validate and optimize the modified structure. Simulation results indicate that the electric field strength is notably higher in the air region near the parallel groove clamp of the traditional structure. The addition of a semiconductor shielding layer in the modified structure effectively suppresses the increase in electric field strength. Power frequency withstand test results further confirm the inhibitory effect of the semiconductor shielding layer on electric field intensity. However, experimental observations reveal occurrences of discharge at the cutoff point of the semiconductor shielding layer. Finally, optimization of the modified structure successfully eliminates the occurrence of discharge at the cutoff point of the semiconductor shielding layer. The final chapter showed the withstand voltage test specified by IEC standard for the IOPPC downlead cable with the structure of the hollow aluminum ball wrapping, confirming the effectiveness of the modified design.