Structure optimization for downlead cable of 110-kV insulated optical-unit phase conductor

Currently, fiber optic communication has become the primary means of communication within China's telecommunications network. Both domestic and international scholars have conducted extensive research on various types of optical cables, achieving significant results. However, to date, there has been no research, either domestically or internationally, addressing the discharge issues associated with the insulated optical-unit phase conductor (IOPPC) in 110-kV transmission lines. In the course of promoting the use of 110-kV lines, there was an incident in Guangdong Province, China, involving the fracture of an IOPPC downlead cable. This paper proposes a modified structure for the IOPPC downlead cable to address the aforementioned fracture incident. First, the finite element method is utilized to calculate the electric field intensity of both the traditional and modified IOPPC downlead cable structures under a voltage of 110-kV. Preliminary verification of the effectiveness of the modified structure is then conducted. Subsequently, the proposed modified structure is verified and further optimized through power frequency withstand voltage tests. Simulation results indicate that the traditional structure exhibits a high electric field intensity in the air region near the PVC cube. In contrast, the addition of a semiconductor shielding layer in the modified structure effectively suppresses the increase in electric field intensity in this area. Power frequency withstand voltage test results further confirm the effectiveness of the semiconductor shielding layer in suppressing the electric field intensity. However, it was observed that discharge phenomena still occurred at the cutoff point of the semiconductor shielding layer. Finally, the modified structure is optimized to effectively eliminate the discharge phenomena at the cutoff point of the semiconductor shielding layer.