Transient Modelling and Backflashover Rate Analysis of a Fully Composite Pylon

A proposal for a fully composite pylon has been designed to meet the requirements of compact structure and elegant appearance for new-generation 400 kV transmission towers, able to save lines corridors and reduce visual impact. Correspondingly, a method of external down-lead has been proposed to bring grounding potential to the shield wires. Based on this design, in this paper, lightning overvoltage level of the fully composite pylon is investigated by using transient simulation tools and backflashover performance is evaluated through Monte Carlo method. An equivalent distributed parameter model of the pylon is established, with the stray capacitances of phase conductors calculated in advance. Monte Carlo method is used to simulate the randomness of lightning current waveform in the nature. The overvoltage levels are simulated in PSCAD to determine the occurrence of backflashover. The backflashover rate (BFOR) is estimated by accumulate the probability of backflashover after repeated random sampling of lightning current. Simulating results show that the BFOR is 0.074 flashes/100 km·year and the overvoltage level calculated becomes lower in the modified model considering stray capacitances. Effects of both the lightning peak current and the tail time on the probability of backflashover occurrence is also summarized.