The lightning performance of a 400kV composite pylon with cable as down-lead

This paper investigates the effect of the impulse corona inside the cross-arm on the lightning performance of a Y-shaped composite pylon with a cable as an internal down-lead through the hollow cross-arm. First, the electromagnetic transient model for the down-lead system of the composite pylon is built. The simplified steps for calculating the surge impedance of the cable down-lead are given. In addition, the mutual coupling between two down-leads is considered. Through a laboratory test on coaxial cylinders resembling the structure of the cable and cross-arm, the dynamic capacitance of the corona on the surface of the cable is obtained and included in the electromagnetic transient model. Then, the effect of the corona on the traveling waveform and mutual capacitance is discussed. Furthermore, the influences of the ground electrode length and the phase voltage on lightning performance are also studied. Finally, the backflash rates of the composite pylon with cable as down-lead are calculated. The results show that the impulse corona has a limited impact on the critical current, and the composite pylon with cable as down-lead shows a promising lightning performance.