Experience Using the Boundary Element Method in Electrostatic Computations as a Fundamental Tool in High Voltage Switchgear Design

In the last ten years we have seen fast development in the computational methods used in all fields of engineering. The possibility of getting rapid and accurate models of High Voltage (H.V.) Switchgear can reduce considerably the high cost of development testing. In this paper the Boundary Element Method (BEM) is discussed from an industrial user point of view. First we analyse the advantages of using the BEM specifically for three-dimensional electrostatic computations. Two examples are presented. One model is an epoxy rod between two coaxial electrodes in which the electrical field distribution around metal inserts, H.V. shields and along the creepage distance is required. Also shown is the calculation of the change of field configuration after a discharge between the contacts of a disconnector. In these examples, a three dimensional analysis is necessary because of the geometry of the problem. These kinds of problems are often found in H.V. engineering and were resolved in the past using much less accurate twodimensional approximations. Introduction Anybody familiar with the design of H.V. Switchgear can realise the slow progress electrical insulation development has experienced in the last 20 years, especially compared with others fields such as electronics. Nevertheless, the fast development in recent years of computational methods has made it possible to resolve electrostatic problems, which in the past we had to approximate by rough models and many expensive tests. These new computational techniques open the door to, if not radical innovation, at least a significant time and cost reduction in the optimisation of the H.V. Switchgear design (2). Boundary Element Method The Boundary Element Method (BEM) is a numerical method for the solution of boundary value problems. In electrostatics, Maxwell’s equations are the governing equations (1). That is, at every point where the surrounding media is continuous: