Optimal Phasing for Parallel Transmission Lines to Minimize AC Interference

AC interference is a growing concern within the power industry due to the proximity of other utilities (pipelines, railways, etc.) sharing the same right-of-way (ROW) and corresponding safety issues. This paper presents a methodology for determining the optimal phasing of power transmission lines to reduce the interference and improve on safe operation of utilities sharing the same ROW. The induced voltage levels on an adjacent conductor are calculated using various existing methods to compare their accuracy. Several important findings are reported here regarding the AC interference modeling under steady-state condition. The importance of the inherent unbalance in phase currents and the effect of soil resistivity are discussed in detail. The test case in the study is based on a project in BC Hydro to build two 500 k V transmission lines located in the Peace Region area, British Columbia. The results of this study were used in determining the optimal phasing for these transmission lines.