Evaluation of Continuous Exposure to Magnetic Field From AC Overhead Transmission Lines Via Historical Load Databases: Common Procedures and Innovative Heuristic Formulas

Public concern about electromagnetic fields from power systems calls for a proper evaluation of continuous exposure of the population to power frequency magnetic fields, especially those from overhead transmission lines, felt as impacting human activities and the environment. Sophisticated measuring and computing tools now available for continuous exposure evaluation may be ineffective without a sound knowledge of power system theory and of typical line loads. In this perspective, the paper firstly recalls the fundamentals of power line magnetic field calculation and shows that a proper use of historical load databases is essential for associating residential magnetic fields with load diagrams of the lines. Then, innovative heuristic formulas for ac double-circuit overhead transmission lines with independent circuits are proposed, so that line databases can be used accounting for phase-shift effects between line currents in an easier and faster way. Such formulas provide a good approximation, via one single fixed-load calculation, of the median/mean magnetic field over a reference operational period of the line (e.g., one year) and are successfully applied to an existing line, resorting to a historical load database of the line recorded from 1994 to 2001.