Abstract:
The results of breakdown voltages in liquid silicone rubber (LSiR) insulation under stepped polarity reversal voltages at a uniform temperature in a needle-plane electrode system are presented in the paper. In the presence of defects like sharp conductor projections or protrusions in the cable insulation stressed under polarity reversal direct current (DC) voltages, the electric field distribution is far more complex due to nonlinear insulation conductivity and time-dependent field distribution. The electric field distribution and space charge accumulation are intricate functions of factors like geometry and nonlinear conduction. In this paper, a two-dimensional (2D) axisymmetric model of a needle-plane geometry is developed using finite element method to compute the time-dependent field, space charge and current density distribution under polarity reversal DC, which, apparently did not get much attention until now. Interesting results on the effect of polarity transition time, applied polarity time step on the above-mentioned distributions are addressed and presented. The pronounced effects of nonlinear conductivity on the time-dependent field distribution are also demonstrated. Furthermore, from the breakdown experiments conducted on tip-plane electrode system for different tip radii and applied time steps, the results put forward a rational and practical estimate of the breakdown field, using the proposed model.
