Since the invention of the transformer, the design, quality and efficiency of this magnificent machine has been improved thanks to the development of electromagnetic materials, computer design algorithms, insulation materials, cooling systems, structural design, etc. Nowadays, a vast number of transformers operate worldwide aiming to provide reliable and safe operation under the most cumbersome environmental and operational conditions.
Even though the materials, design and manufacturing processes have improved, the most common insulation system is a combination of liquid insulation, cellulose and impregnated in oil cellulose. These components of the overall insulation system go through an inevitable aging process that leads to the end of the service life of power and distribution transformers. One can expand this statement into other components with similar insulation construction such as bushings and instrument transformer with oil-impregnated paper insulation.
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