Magnetic-Field Calculation Under EHV Transmission Lines for More Realistic Cases

Ground level electric and magnetic fields from overhead power transmission lines are of increasingly important considerations in several research areas. Common methods for the calculation of the magnetic fields created by power transmission lines assume straight horizontal lines parallel to a flat ground and parallel with each other. The influence of the sag due to the line weight is neglected or modeled by introducing an effective height for the horizontal line in between the maximum and minimum heights of the line. Also, the influences of the different heights of the towers, the different distances of the power transmission lines´ spans, and the different angles between the power transmission lines´ spans are neglected. These assumptions result in a model where magnetic fields are distorted from those produced in reality. This paper presents a complete technique, with the effect of the conductor sag is taken in the account, to calculate the magnetic-field intensity at any field point above or near the earth´s surface, from any numbers of spans of various configurations; namely, unequal heights of the towers, unequal spans between towers, and the power transmission lines´ spans are not parallel to each other. This complete technique is applied on the Egyptian 500-kV single-circuit overhead transmission line, and the investigations of the number of spans, the angle between spans, the span length, and the heights of the towers are discussed and compared with the results obtained from the common two-dimensions straight-line technique.