ABSTRACT
Insulation of power transformers represents a complex system consisting of various design components. The insulation may be divided into two parts: internal insulation and external insulation. Internal transformer insulation is divided into main and longitudinal insulation of windings, insulation of bushing installation, insulation of taps, and tap changer. The main insulation of windings is insulation from the given winding up to earthed parts of core, yoke, tank, and other windings. Longitudinal insulation is the insulation between various points of one winding: between turns, layers, and coils. Insulation of transformers in service is exposed to continuous actions of operating voltage and transient overvoltages. Coordination of internal insulation demands to provide withstanding of all voltage stresses during the lifetime of the transformer. In the oil-barrier insulation, the most stressed gaps are gaps joined to windings because it is necessary to expect substantial growth of the electric field intensity due to the heterogeneity brought in by elements of the winding design.
