Calculation of the Potential Gradient of Twin-Cylindrical Bipolar Conductors with Various Geometrical Parameters

All theoretical methods for calculating corona thresholds in a nonuniform electric field depend on precise knowledge of the field distribution near the stressed electrode. The charge simulation technique and the method of images were applied to two twin parallel cylindrical conductors, all located in the same horizontal plane above ground. The charge on the positive and negative subconductors is represented by several lumped charges, and a set of equations are developed whose simultaneous solutions yield equipotential surfaces on the conductor's circumference. These equations were solved for the magnitudes of the lumped charges, whose optimum locations were determined by considering the results over a wide range of line dimensions. A digital computer program was developed to provide values for the potential and electric field, magnitude, and direction anywhere in the gap. The error in computing the electrode surface potential is about 0.02%. When applied to bundle-conductor lines, this method has no restrictions with regard to spacing between the bundles or height above ground. A study on the effect of varying the line geometrical parameters on the potential and electric field has revealed interesting relations.