Lightning performance of transmission lines based upon real return-stroke current waveforms and statistical variation of characteristic parameters

This paper presents investigative studies concerning the lightning performance of 500 kV transmission lines considering the characteristic parameters of first stroke current observed in measurement data along with its statistical variation. Therefore, advanced electromagnetic models were applied during the development of computational models, thus allowing a realistic representation of the first stroke current waveform. Lightning performance studies were conducted applying two of the most commonly used return-stroke current models, besides the first stroke current model recommended by CIGRÉ. The aim therefore is to identify which of these present the most accurate results, when compared to the use of real return-stroke current waveforms. The volt-time characteristics produced by each of the return-stroke current waveforms were evaluated using both the leader progression model (LPM) and volt-time curve. The breakdown process modelled through LPM is able to represent accurately the physical process established along the perimeter of the insulator strings, during a backflashover event. Analysis of leader length and velocity can reveal the influence of particular characteristics of lightning overvoltage waveform across the insulators produced by different return-stroke current waveforms in the assessment of the lightning performance of a transmission line. The computational modelling developed herein, allows identifying the critical current, the amplitude of the overvoltage that produces the backflashover, and the instant of time that breakdown occurs. The proposed modelling also makes it possible to determine in which insulator string and tower the backflash happens.