Influence of corona on the voltages induced by nearby lightning on overhead distribution lines

Abstract

tereseinterg pt F. Rachidi Montena EMC CH-I 728 Rossens Switzerland farhad.rachrdi@epfl ch ..lbslract -4 model for the calculation of lightning-induced voltages is presented with the aim of assessing the effect of corona when power distribution lines are illuminated by lightning electromagnetic fields. Corona is taken into account by means of dynamic capacitance describing a charge-voltage diagram. Such an equivalent capacitance is then introduced in a model which describes a line illuminated by a lightning electromagnetic field. It is first concluded that the influence of corona on lightning induced overvoltages is of importance only for particularly severe strokes. It is also found that corona acts to increase the magnitude of these overvoltages, contrary to the case of voltages doe to direct strokes, which are attenuated by corona. A theoretical explanation of such an amplitude increase is presented. The effect of the ground resistivity is also taken into account in the calculations. The results show that such an effect is in general as important as the effect of corona. This is different from the direct-strike behavior, where corona, when present, affects the surge propagation more than the ground resistivity. This is due to the fact that for the case of induced-voltages, the ground resistivity may affect more strongly the lightning-radiated fields rather than the surge propagation along the line, while corona affects only surge propagation. The need for experimental results to test the theoretical finding of the paper is stressed and some indication is given. Finally, a sensitivity analysis of the induced voltages as a function of the charge-voltage diagram adopted to model corona is also performed.

On the influence of corona on lightning-induced overvoltages

“…As expected the results reported in the paper do not differ qualitatively from those presented in [8,9], namely, the corona phenomenon acts in enhancing the amplitude of lightning-induced voltages. The explanations for such a somewhat unexpected behaviour have been given in [9].…”

“…The line configuration used in this study is the one adopted in [9]. In particular, it is composed by a 1-km long, 7.5-m high, single-conductor overhead line (see Fig.…”

“…The approach adopted in the paper for the calculation of the field-to-transmission line coupling in presence of corona is the same illustrated in [9]. It is based on the extension of the field-to-transmission line coupling equations of Agrawal et al [10] in order to take into account both the presence of a finite conductive ground and corona.…”

“…In this respect, the evaluation of the influence of corona on lightning-originated surges has been treated both for the case of direct strokes to high voltage transmission lines (e.g. [2][3][4][5][6][7]) as well as for the case of indirect lightning-induced voltages in medium voltage distribution lines [8,9]. As known, this non-linear phenomenon is one of the responsible in the travelling waves surge distortion and its effects for lightninginduced overvoltages are as important as those associated to the finite ground conductivity.…”

“…Following the approach proposed in [9], based on the integration of the dynamic capacitance concept into the field-to-transmission line coupling equations of the Agrawal model [10], the paper presents some calculations obtained using an experimentally inferred charge-voltage (Q-V) diagram used to macroscopically model corona. In this paper, for the representation of the corona dynamic capacitance use is made of the Q-V expression proposed in [11].…”