A Physical Model for Inception and Propagation of Upward Lightning Leader from a 1200 kV

Where [5] is a geometrical factor that considers the effect of all the streamers on the total charge in the corona region and A is the area of the region between the background potential distribution for few metres ahead of the object on the ground and a straight line curve whose slope is the constant streamer potential gradient, Estr = 450 kV/m [5, 10] in the distance-voltage curve. Once the corona inception occurs, the charge on the corona region is calculated for every step of the descending downward leader using equation (1). When the charge on the corona region exceeds 1 µC [5, 10] unstable upward leader is incepted from the object on the ground and calculation for stable upward leader inception begins. The length of the unstable leader is calculated by
Anurag A. Devadiga
Department of Electrical Engineering Indian Institute of Science Bangalore, India anuragd@ee.iisc.ernet.in
M. Joy Thomas
Department of Electrical Engineering Indian Institute of Science Bangalore, India jtm@ee.iisc.ernet.in
978-1-4799-3544-4/14/$31.00 ©2014 IEEE
1969
object on the ground. Once the corona inception occurs, the background potential distribution for few metres ahead of the object on the ground is computed. The charge in the corona region is given by
The lightning downward leader is considered to be descending in steps of 10 metres from the bottom of the cloud towards the ground. The charge distribution for the downward leader considered in the present model is given by Cooray et al. [7]. The field on the object at the ground due to cloud charges is influenced by space charge near ground and is taken to be a constant field of 7.5 kV/m in the present model [8]. The transmission line, and the upward leader channel that emerges from the line are modeled as a conductor whose line charge density is a piecewise linear function [9]. The computation for leader inception and propagation is done using charge simulation method. The downward leader approaches the ground from the cloud in steps and this in turn leads to increase of electric field in the vicinity of the object on the ground. When the electric field on the object at the ground due to the approaching downward leader is greater than the corona inception field given by the Peek’s criterion, then corona is incepted from the
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leader inception, i.e., corona inception, unstable and stable upward leader inception from the object on the ground. Upward leader inception [3] and propagation [4] models proposed by Becerra and Cooray, even though deals with the detailed physics of lightning, are complicated and they also require large computational time. This paper focuses on the upward leader inception and propagation from a 1200 kV ac power transmission line. Present upward leader inception model is based on background potential distribution ahead of the upward leader tip [5]. The upward leader propagation model is based on the correlation between the induced voltage on the conductor due to the lightning downward leader channel and the drop along the upward leader length [6].
Abstract—UHV power transmission lines have high probability of shielding failure due to their higher height, larger exposure area and high operating voltage. Lightning upward leader inception and propagation is an integral part of lightning shielding failure analysis and need to be studied in detail. In this paper a model for lightning attachment has been proposed based on the present knowledge of lightning physics. Leader inception is modeled based on the corona charge present near the conductor region and the propagation model is based on the correlation between the lightning induced voltage on the conductor and the drop along the upward leader channel. The inception model developed is compared with previous inception models and the results obtained using the present and previous models are comparable. Lightning striking distances (final jump) for various return stroke current were computed for different conductor heights. The computed striking distance values showed good correlation with the values calculated using the equation proposed by the IEEE working group for the applicable conductor heights of up to 8 m. The model is applied to a 1200 kV AC power transmission line and inception of the upward leader is analyzed for this configuration. Keywords-Lightning; Lightning striking distance; Upward leader inception; Transmission line
2014 International Conference on Lightning Protection (ICLP), Shanghai, China
A Physical Model for Inception and Propagation of Upward Lightning Leader from a 1200 kV AC Power Transmission Line
II.
METHODOLOGY
I.
INTRODUCTION
The probability of the lightning attachment to the power carrying conductor in a UHV transmission line is very high due to their higher height, larger exposure area and very high operating voltage. Shielding failure analysis for a transmission line mainly involves propagation of lightning downward leader, inception and propagation of upward connecting leader from the object on the ground and final jump (striking distance) between the two leaders. For the past few decades models such as electrogeometric model (EGM) [1] and leader progression model (LPM) [2] have been developed to study the shielding failure of power transmission line. EGM and LPM in their initial stage do not deal with the detailed physics of upward