Computational aspects of transient fields associated with insulation breakdown in GIS under inhomogeneous fields

The phenomena of leader inception and propagation leading to breakdown in strongly attaching gases like SF₆ are currently being studied because of their relevance to the design of High Voltage Gas Insulated Systems (GIS). Breakdown of SF₆ gas under inhomogeneous fields is known to be by the leader mechanism. The leader propagation is guided by the electric field at the leader tip, which in turn is dependent on the nature of voltage applied, electrode geometry and charge distributed in the leader. The charge build up process in the leader is governed by Resistive-Capacitive (R-C) transient fields. In such fields, both permittivities and conductivities of the participating medium determine the field distribution. The scope of the present paper is to discuss the important aspects of computing R-C transient field associated with the leader in SF₆ gas modeled as a straight cylindrical conducting channel. Studies are carried out under unit step voltage excitation for two leader lengths and assumed conductivity of the leader. The workability of the R-C transient field computing algorithm for such studies carried out with the help of a Laplace solver are presented and discussed