Design improvements on graded insulation of power transformers using transient electric field analysis and visualization technique

This paper deals with design improvements on the graded insulation of power transformers using transient electric field analysis and a visualization technique. The calculation method for transient electric field analysis inside a power transformer impressed with an impulse voltage is presented. Initially, the concentrated electric network for the power transformer is constructed by dividing the transformer windings into several blocks and by computing the electric circuit parameters. Next, a transient electric field analysis is performed. Using the results of the circuit analysis as boundary conditions, a 2-D axisymmetrical electric field finite element analysis is performed. Finally, an animated display technique for the transient voltage, the electric field intensity and the tolerance rate of electric field intensity distributions is proposed as an extremely useful tool for design on graded insulation. A successful application of the proposed method for analysis of a model transformer for which the computed results agree very well with measured results is also presented.