In recent years, the possibility for ac and dc transmission lines running parallel to each other, sharing the same right-of-way (ROW) or even the same tower has been increased. Design of such hybrid ac/dc networks requires a precise calculation of the electric field around and under them. This paper presents quantitative analysis of the electric field at 1 m height above ground surface for different hybrid ac/dc transmission lines. Lateral profiles for typical Egyptian 500, 220 and 132 kV after adding bipolar de lines are presented. The gaper also considers reconfiguration of a typical 220 kV Egyptian double-circuit ac transmission line, in which one of the circuits is converted into +/-220 kV bipolar dc line. Different reconfiguration alternatives are studied to choose the optimum arrangement. The charge simulation method (CSM) employing the superposition principle is used to calculate the RMS value of the electric field generated by hybrid ac/dc lines at any point in the space. The RMS values of the held are determined directly without dividing the ac supply cycle into a sufficient number of subintervals as it has been done before. Satisfactory agreement with the results measured and calculated before by other techniques, for some typical ac/dc lines, has been obtained. Copyright (C) 2000 John Wiley & Sons, Ltd.