Electrothermal Optimization of Field Grading Systems of Station Class Surge Arresters

An electrothermal simulation based procedure for the optimization of the held grading systems of station class surge arresters is presented. The main difficulty consists in the numerical solution of the three-dimensional (3-D) held grading system, and the transient electric held problem that arises when a held grading system is introduced. Therefore, we first develop an equivalent axisymmetric arrester model that can reproduce the electric held stress in the resistor column with high accuracy. The model employs a special virtual electrode geometry whose shape and position are determined by a multi-parametric optimization procedure. On the basis thereof, a numerical optimization of the 3-D grading system for an arbitrarily large arrester can be efficiently performed on the basis of transient, electroquasistatic simulations of its axisymmetric equivalent. This procedure is demonstrated for the standard International Electrotechnical Commission (IEC) surge arrester. The detailed electrothermal analysis of this arrester shows that an immense improvement of the held and thermal stress distribution in the resistor column can be obtained.