Electrostatic and environmental analyses of high phase order transmission lines

This paper presents an electrostatic modeling and environmental effect analysis of the high phase order transmission lines (HPOTL) using the charge simulation method. Both the conversion of the existing EHV and UHV double circuit transmission lines to six-phase lines, and the use of new, compact circular configuration HPOTL are introduced and discussed in the light of electric field computation at both the subconductor/conductor surface and the ground level. A new technique is also presented to decrease drastically the electric field at the ground level with a negligible increase in the conductor surface gradient and the charging current of the bottom phases. In this technique, a very few number of extra ground wires under each circuit are added, where they can also be utilized as optical ground wires for telecommunication purposes. Different phase arrangements, voltage ratings and conductor coating of the above-mentioned two cases are studied to investigate the possibilities of increasing the power handling capabilities without augmenting the environmental effects. It seems that HPOTL give a promising cost-effective means for increasing the power handling capability either for the existing double circuit transmission lines by 73% via increasing the operating voltage, or for the compact HPOTL via using six or more phases.