Magnetic and electric field near overhead line towers

Since it is hard to disconnect important overhead power lines outside the foreseen terms, the maintenance personnel have to move on environment exposed to electromagnetic fields. The applicable guidelines for safe work under operating lines define the limit distances between of the maintain personnel and live conductors. In practice, human sensitivity of the invisible electromagnetic fields on towers is also restraint at maintenance. Certain tower types are more acceptable from standpoint of electromagnetic fields as second, although the distance measured to source is the same. As seen from literature, the issue of electromagnetic fields near overhead transmission towers has not yet been discussed. Most of the authors deal with calculations of the electromagnetic fields near overhead power line primary concentrated with conductors [1]. The idea of field calculations discussed in this paper is basically used in high voltage substation fields [2,3]. Our focus was on the magnetic and electric field calculations, for the three-dimensional structure of line towers. In both calculations the overhead tower elements and conductors was divided into an equivalent assembly of sticks of the final length. Calculations of the corresponding charges and currents on and in it were made next. By dividing the elements we define the use of the moment method, where test functions are pulses of the same width as stick elements. In the calculation model, all the tower elements, which are of a noncircular form, are translate into the equivalent form shown in figure 1. Equivalent radius covers the surface area of the original element. First, we determine equation for the vector magnetic potential of the current stick. To calculate magnetic field, all the currents in conductors and tower structure elements have to be known. The currents are determined through the model circuit of magnetically connected branches and analyses by the tools of the electric circuits (5). The land contribution to primary magnetic field is neglected. The magnetic field is calculated by using the Biot-Savart law with summarizing all the sources (6). To calculate the electric field, the scalar potential equation on the elements surface is used and the land contribution is taken into calculation (7). First, the conductor potential is known. Second, from the magnetic field analyses the scalar potential of all of the structure sticks are determined. We then join the magnetic and electric considering views, so far separated in the quasi-static approach. Here is the difference between us and other authors' who assume the potential of a grounded structure to be equal to zero. By using new approach, charges on sticks are calculated. Then electric field in an arbitrary point is calculated as a sum by using the Coulomb and Faraday law (12). All calculations were made with the Matlab tool. At first, the overhead line geometry and tower structure are made. They are obtained from determination of the sticks start and end points, internal impedance of sticks and primary source values. In the second part we calculate the matrix coefficients regarding the magnetic and electric equations. Coefficients are expressed with double integrals, which are solved numerically. Our results show that perturbation of the magnetic field is weak and of the electric field is strong. Our numerical results, too, confirmed the maintainers observations that electric field strengths, that it is achieved near 400 kV overhead towers, the geometry of single circuit line tower in shape Y is less favorable from double circuit barrel tower, from human sensitivity standpoint. The presented electric and magnetic field calculations can be used and extended for any shape of electric structure.