Evaluation of Backflashover Taking Induced Voltages by Return Stroke Current into Considerations

Abstract

A new evaluation method of backflashover due to lightning stroke was proposed taking induced voltage on an horizontal line caused by return stroke current corresponding to tower current into considerations, which is not evaluated in conventional study. The new method became possible by the approach that the analysis program of induced voltage by EMTP (Electro Magnetic Transients Program) was developed and it could be assembled in general circuit analysis.
In the new method the terminal voltage of an horn gap of transmission line is tolerably higher than in conventional study because induced voltage on a line has reverse polarity compared with that of tower voltage by stroke and therefore those differential voltage is applied to an horn gap.
Consequently, flashover of an horn gap is easy to occur not only in upper phase, but also in middle or lower phase and the response voltage of a substation is higher. Surge voltage wave in the new method agrees with that measured in field substation better than in conventional method.