Transformer Insulation Design Based on the Analysis of Impulse Voltage Distribution

Abstract

In this chapter, the calculation of transient voltages over and between winding parts of a large power transformer, and the influence on the design of the insulation is treated. The insulation is grouped into two types; minor insulation, which means the insulation within the windings, and major insulation, which means the insulation build-up between the windings and from the windings to grounded surfaces. For illustration purposes, the core form transformer type with circular windings around a quasi-circular core is assumed. The insulation system is assumed to be comprised of mineral insulating oil, oil-impregnated paper and pressboard. Other insulation media have different transient voltage withstand capabilities. The results of impulse voltage distribution calculations along and between the winding parts have to be checked against the withstand capabilities of the physical structure of the windings in a winding phase assembly. Attention is paid to major transformer components outside the winding set, like active part leads and cleats and various types of tap changers.