| Popis: |
Several models of earthing systems under high impulse conditions, which are in satisfactory agreement to the experimental results, have been proposed in previous studies [1-11]. However, these models do not consider for the effects of current rise time as the voltage levels were increased. In earlier work [11], it was observed that the current impulse shape exhibited two current peaks with some time delays; where the times t1 and t2 are the time to the first and second current peak respectively. Both time delays were found to be lower for higher conductivity soil and also to decrease with voltage magnitudes. A model of earthing systems was also proposed by the authors [11], which consisting of the capacitance in parallel with the non-linear resistance. However, this non-linear resistance function cannot reproduce the dependence of current time-to-peak on voltage magnitudes. This present paper attempts to address this shortfall and to extend an earlier work [11]. Using the same laboratory data as in [11], an improved equivalent circuit for earthing systems under impulse conditions has been proposed, which considers the effect of a decreasing time-to-current peak as the amplitude of the current/voltage increases. Some models of earthing systems under high impulse conditions developed in previous work are also presented in this paper. This allows a better understanding on the characteristics and the parameters of the soil under high impulse conditions. |
