Feasibility of cable through a hollow cross-arm as down-lead for a 400 kV Y-shaped composite pylon

The down-lead system allows the direct strokes to be conducted efficiently to the ground and plays a vital role in the lightning protection of transmission towers. In this paper, the feasibility of a cable as a down-lead for a 400 kV composite pylon with the ‘Y’ pattern is investigated from the perspectives of the electrical insulation and lightning performance. A 3D full-size model is built in COMSOL to study the electric field distribution inside of the pylon cross-arm. Meanwhile, two coaxial Fiber Reinforced Plastic tubes are used to resemble the structure of a cable passing through a hollow cross-arm. The corona inception electric field on the surface of the cable with different radii under AC 50 Hz applied voltage and the corona characteristics under switching overvoltage are analyzed. Based on experimental tests, the cable parameters are determined. Then, an electromagnetic transient model for the pylon down-lead system considering impulse corona effect has been built in PSCAD/EMTDC and the backflashover rate is obtained. Finally, the cable insulation strength under the transient overvoltage is validated by lightning test. The research shows that a cable with appropriate dimensions used as a down-lead can meet electrical insulation requirements and presents a good lightning performance.