Influence of accelerated thermal ageing on the performance of alternative solid dielectrics for power transformers

In the present paper, the influence of accelerated thermal ageing on the performance of alternative solid dielectrics for power transformers, namely thermally upgraded Kraft (TUK), Nomex 910 and Nomex 410 in conjunction with mineral oil, has been investigated. To analyse the properties of these solid dielectrics with mineral transformer oil, accelerated thermal ageing has been carried out at various temperatures ranging from 100°C to 220°C. Furthermore, in order to compare the operating performance of transformer insulation, several electrical, thermal, physical and chemical properties of transformer oil, including breakdown voltage, interfacial tension (IFT), water content, absorption coefficient and colour factor, have been determined. Subsequently, the breakdown voltage and tensile strength of different solid dielectrics have been determined. It has been revealed from the test results that Nomex-impregnated oil samples have shown better thermal performance and oxidation stability than thermally upgraded Kraft-based oil samples. Also, these samples consist of fewer dissolved decay contents and sludge. Therefore, Nomex materials are suggested as alternative solid dielectrics for power transformers. These solid dielectrics provide a long service run and reduced operating and maintenance costs of transformers. It is envisioned that the present experimental study will be very beneficial for utility managers of transformers.