Performance Evaluation of Thermally Stressed Solid Dielectrics for Transformers

An experimental study to determine the furan contents of mineral transformer oils impregnated thermally upgraded Kraft and Nomex-910 has been conducted in the present study. Oil samples with thermally upgraded Kraft and Nomex-910 were thermally stressed at different temperatures ranging from 120°C to 180°C. Further, high performance chromatography and Raman spectroscopy tests were performed on each of the aged samples. It has been determined from test results of both techniques that the furan contents produced in thermally upgraded Kraft oil samples is higher than that of Nomex-910 impregnated test samples. Degree of polymerization which determines the degradation of the dielectric for thermally upgraded Kraft oil sample at 120°C is 905 and at 180°C is 309. Whereas, degree of polymerization for Nomex-910 impregnated oil sample varies from 927 at 120°C to 362 at 180°C. It is concluded from the experimentation study that the degradation rate of Nomex-910 insulating paper is lesser than that of thermally upgraded Kraft. Nomex-910 samples have better thermal performance and higher life than that of the thermally upgraded Kraft samples. It is expected that the present experimental investigation shall be highly beneficial not only to the transformer utilities but also to the customers.