Computation of electric stress and corona onset voltage in air gaps with floating particles

From the standpoint of the gas insulation design, the most important factors in discharge performance is the corona starting voltage and the flashover voltage. The main problem of insulation design will be solved if the corona onset voltage and flashover voltage are calculated for given electrode arrangement. In this study a general computer program using Matlab is developed to predict the discharge inception voltage levels in sphere-to-sphere gap with the presence of floating conducting particles in air insulated DC power apparatus. Therefore, through out the computations of discharge inception voltages, streamer theory is considered. The streamer theory closely associated to the electric field distribution inside the gap, in order to compute the critical single avalanche size which is responsible for initiating the streamer channel at the discharge inception voltage. The floating metals particles treated in this work are rectangular plates, needles with hemispherical ends and spheres. As a theoretical base, a charge simulation program has been carried out to determine the effect of floating particle in electric field distribution along the gap axis between two sphere electrodes. The dependence of field enhancement and its distribution and corona inception voltage within the floating particle on the shape, size and location of floating metal and the electrode spacing are emphasized. The results concluded that the enhancement of electric field depends on the Shape but in all case the electric field is distorted. The results show that the effect of various parameters on the stress distribution within a floating metal particle is important in the design and testing of dielectric insulating materials.