Determining EHV transmission line magnetic fields by applying the vector magnetic potential concept

Abstract

These days renewed attention is being given to the biological effects of non-ionizing radiations from the power frequency electromagnetic fields of extra-high-voltage (EHV) transmission lines. Prior to fixing limits about the safe levels of human exposure to such radiation, it is essential to determine its field magnitudes. In this paper the concept of vector magnetic potential has been extended for a multiphase multiconductor transmission line and expressions for the flux densities of the resulting magnetic field components have been developed. This approach for determining the transmission line magnetic fields quantitatively is new and straightforward. It requires only easy-to-obtain physical parameters having specific values and involves no uncertainty. The proposed approach was applied to determine the magnetic field distribution within and beyond the rights of way of five transmission systems at 132, 230, 345, 500 and 765 kV. The results obtained were in close agreement with the measured field values. The proposed approach is expected to be useful for transmission line designers as a convincing and fast analytical tool for designing the allowable line current magnitude, conductor height and spacings, and number of circuits in order to result in a prespecified magnetic field. However, the results reported herein are expected to benefit researchers engaged in assessing whether magnetic fields of the orders of magnitude obtained for various transmission systems can have any adverse effects on the health of living beings exposed to the lines.