A Study of the Initial Surge Distribution in Concentric Transformer Windings

Certain properties of transformer windings in their response to lightning surges are investigated by a systematic study of the initial surge distribution, that is, by excluding the time effect. The investigation is further confined to stresses between layers or pancakes and between turns of concentric windings and to the voltage distribution between such windings and grounded parts. Insulation grading is considered. The influence of static shields at the line ends is given special consideration based on a new analysis of the series capacitance. By comparing the calculations with measurements of the electric field distribution on resistance paper, some limitations in replacing the actual field problem by circuit problems are uncovered and suitable approximations are developed for obtaining a practical solution.