Optimisation of the dielectric strength of a non-uniform electric field electrode system under positive DC voltage by insertion of multiple barriers

The main objective of this work is the study of the flashover voltage evolution of the air gap of two non-uniform electric field systems as a function of the number of screens inserted in the gap, their position, their isolation and their surface conductivity. The results from this analysis show that in the case of clean and dry atmosphere, Dualscreen isolation systems with rod-rod and rod-plane configurations is respectively 50 % and 19 % higher than the case of one screen of the same size. Above this value, no further improvement in dielectric strength is found. The isolation of the two barriers by a solid insulating shield, in contact with each other and a conductive grounded base wall, led economically to an important reduction of insertion device size and technically, its optimum withstand voltage remains the same as that obtained in the case of an air isolation layer of the same size. For low conductivity of the polluting solution, uniformly covering both screens of the rod-rod system, the minimum disruptive voltage value is reduced by over 50 % compared to that obtained under clean atmosphere, so that these polluted insulating screens barriers had become conductive. So if no cleaning of them is expected in polluted sites, the improvement of isolation provided by adding a second screen to the base system will be completely lost during a low contamination of these barriers and we can add that a single screen system is 24 % more rigid than dual-screen system under the same pollution conditions.