Electric field distribution of sphere-plane gaps : A SIMULATION APPROACH

Abstract: The continuous increase of the voltage levels in power transmission systems has lead to the occurrence of higher switching transients during their operation. The design of equipment and grid components able to sustain such a stressful operation, requires an intensive study of the electric field stress generated by these transients, and their distribution to the vicinity of each configuration. Sphere-plane gaps are the most theoretically and practically interesting electrode configurations. So far, the majority of the conducted work is referred to the study of the discharge characteristics of this structure. However, a study of the electrostatic electric field is required. An accurate calculation of the electric field can contribute significantly to an even better understanding of the discharge characteristics and the principles behind them. In this project, is presented a simulation approach for the calculation of the electro-static field of a sphere-plane configuration, varying the dimensions of the sphere and the gap distance. For this purpose, a Finite Element Method (FEM) solver was used, in which the configuration was designed and the numerical solution of the problem was implemented. After that, an attempt was performed to specify the breakdown voltage based on the electric field calculation and distribution. Useful results were recorded from both the simulation of the electrostatic model and the calculation of the breakdown voltage. One of the most important findings, was the specification of an approximate relation between the diameters of the sphere and the tube where this is mounted. As a consequence, the study of the electric field distribution became easier, while at the same time an accurate calculation of the breakdown voltage was achieved. A series of validations were performed, through the comparison with the already ex-isting, published and unpublished, experimental tests and a number of conclusions were listed. One of the most significant, was the specification of the correlation between the electrostatic model and test measurements and how these different approaches can be linked to each other in a practically efficient way. At the end, there is a proposal for further work on the subject, and possible improvements of the already conducted work.