The Role Played by Current Phase-Shift on Magnetic Field Established by Double-Circuit Overhead Transmission Lines - Part II: Dynamic Analysis

The “static” analysis (relevant to fixed load conditions) of current phase-shift effects on magnetic field from ac double-circuit overhead transmission lines (Part I of this study) becomes here “dynamic” by considering time-varying load conditions of an existing line, derived from a database recorded from 1994 to 2001, thereby showing that current phase-shift plays a major role also when load changes. Indeed, often extreme field values over a time period are not associated with extreme current values, but with current phase-shifts that, for given line geometry and conductor arrangement, yield the most effective field enhancement/reduction. An estimate of the mean/median phase-shift angle over a reference period is proposed, that provides a good approximation, via one single static calculation, of the mean/median magnetic field profiles calculated over that period (e.g. one year). It is confirmed that current phase-shifts are fundamental for understanding the behavior of magnetic fields from ac double-circuit overhead transmission lines.