Ageing Components and By-products: Main Structures

A power transformer is composed of a core, set of windings, oil, tank, bushings, tap changer and other auxiliary equipment. Each of these components is manufactured from either metals or compounds that are organic in nature. The different types of material react differently to the different fault conditions and the rate of energy release in the vicinity. This study examines the effects of the energy dissipated and the rate of breakdown of the different materials. These materials consist of kraft paper, oil, copper, steel and insulating boards.

The transformer tank is manufactured from steel and houses the oil and active part of the transformer. The tank has to be properly earthed and can sometimes be subjected to circulating currents causing localized hot spots.

The transformer core provides the medium for the flux path. It is usually manufactured from steel, which is arranged as thin laminations for reducing the effects of eddy currents. These laminated sheets are usually coated with a layer of special varnish or shellac [Gottlieb1]. The core arrangement is usually constructed in either the core or the shell type arrangement. The core type arrangement is such that the magnetic core is surrounded by the low voltage and high voltage windings [Heathcote1]. In the shell type arrangement the windings are surrounded by the core. GSU Transformers are usually of the core type arrangement. The core arrangement also can have a variation on the number of limbs. In a five limb core type transformer the three phase windings are located in the inner three core legs respectively and the outer legs on either side allow for flux transfer.

GSU transformers are constructed as two winding transformers. The low voltage and high voltage winding per phase are located in close proximity to ensure the maximum mutual coupling between windings [Winders1]. The windings are composed of thin copper strands, which are wrapped with paper insulation. 

References

[Gottlieb1]	Gottlieb, I. M., “Practical Transformer Handbook,” Reed Educational and Professional Publishing Ltd., India, 1998
[Heathcote1]	Heathcote, M. J., “The J & P Transformer Book,” Thirteenth Edition, Newnes, 2007
[Winders1]	Winders, J. J., “Power Transformers: Principles and Applications,” Vol. 17, CRC, Allentown, Pennsylvania: Marcel Dekker Inc., 2002