The use of rational B-spline surface to improve the shape control for three-dimensional insulation design and its application to design of shield ring

In this paper, a three-dimensional algorithm for the insulation design of the high-voltage equipment is presented. In general, the insulation design consists of two steps. One is the electric field calculation. The other is the correction of the shape of the electrode or the insulator to be designed. The main point of this paper is the introduction of the rational B-spline to improve the shape control for the insulation design. In former research, the correction of a shape is made by direct control with the nodes on the shape. This required many design variables and causes the discontinuous curvature of a designed shape. These problems can be dealt with by the indirect control which is one of the useful properties of the rational B-spline. The use of rational B-spline results in the reduction in the number of design variables and guarantees the smooth curvature of the designed shape. The proposed algorithm is applied to the design of the shape of the shield ring which is installed in the joint of transmission lines and the insulator and has been designed by the method of trial and error. The combination method of charge simulation method (CSM) and surface charge simulation method (SCSM) is used to calculate the three-dimensional electric fields produced by this system.