Modeling of transmission line exposure to direct lightning strokes

Abstract

The paper introduces a new model for assessing the exposure of free-standing structures and horizontal conductors above flat ground to direct lightning strokes. The starting point of this work is a recently developed criterion for positive leader inception, modified to account for positive leaders initiated under the influence of a negative descending lightning stroke. Subsequent propagation of the posltive leader is analysed to define the point of encounter of the two leaders which determines the attractive radius of a structure or the attractive lateral distance of a conductor. These parameters are investigated for a wide range of heights and return-stroke currents. A method for analysing shielding failure and determining the critical shielding angle is also described. The predictions of the model are compared with field observations and previously developed models.

Effect of tall instrumented towers on the statistical distributions of lightning current parameters and its influence on the power system lightning performance assessment

“…Expression 2 is an approximation of the formula proposed by Love [16] using the exponential format [6]. Other expressions, namely those by Eriksson [17], Rizk [18], Dellera and Garbagnati [19,20] are available; they have been inferred more recently by regression analysis, from the results of more complex and physically oriented models than the Electrogeometric one. For these expressions, a formula of the following type can be used for the attractive radius…”

“…Concerning the Rizk expression (expression 4), in [18] an analytical formula is proposed for horizontal conductors with height range of 10 m and 50 m and for lightning currents with I p in the range 5-31 kA. The parameters are those of Table II Fig.…”

“…Nucci, M. Paolone T measurements), to obtain a median value for open ground equal to 23 kA. To perform this calculation the lateral distance expression proposed in [18] was applied, which is of the same exponential type assumed by Pettersson in order to derive its formula.…”

“…There is, however, general concern on the fact that these distributions are affected by the presence of the tower; lightning current amplitudes, in particular, are 'biased' towards higher values [8][9][10][11][12][13], as the so-called attractive radius of the tower tends to increase for flashes with larger currents 1 . There are indeed several expressions for such an attractive radius [15][16][17][18][19][20], all predicting its increase with the return-stroke current.…”

Attachment of lightning flashes to grounded structures

“…Both leaders are modeled by line charges and are assumed to approach with a relative velocity ratio equal to four immediately after the upward leader initiation and equal to one close to interception. Later, Rizk [67,69] presented a similar leader propagation model than Dellera and Garbagnati, but based on his own leader inception model [70]. The propagation of the upward leader is simulated by considering a unitary velocity ratio and the vector velocity directed towards the tip of the unperturbed downward leader.…”