Heidari - Tavanir Co.,P.O.Box. ۱۴۱۵۵-۶۴۶۷ Tehran-Iran

Lack of existance of sufficient right of way for construction of new power transmission lines , execution problem faced by underground cables , high price of land , environmental issue , adverse effects of electromagnetic fields of high voltage on living bodies, interference on communication lines , Radio & Television interference and other similar cases make the utility companies to think less about the construction of the transmission lines in new corridor. Under such a circumstances there is no other alternative but to contain with the existing possibilities for the development of electrification network. In recent years , bundle transmission lines due to its specific characters have, received more attention by power network designer for both urban area as a solution to the problem of safety corridor as well as for non urban area as a substitute for EHV lines . In bundle overhead transmission lines by increasing the number of subconductors , the reactance of lines will decreas and the suseptance of line will increase , in such a case , capcity of line , SIL and Stability limit will increase and power & energy losses and voltag drop will decrease . Under such a condition it is ossible to equalize two different classes of voltage In this paper it is tried to show that,in the most cases increasing the subconductors number,is more advantageous than increasing line voltage particularly in the urban areas