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 the magnetic field from ac double-circuit overhead transmission lines (Part I of this paper) becomes "dynamic" here 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.