A Comparative Analysis of Characteristics of PPS and PTFE under Electrical-thermal Aging in Mineral Oil

With the continuous improvement in the transmission voltage, it is increasingly difficult for the oil-paper insulation to meet the strict requirements of the high-voltage that the insulation system should have large capacity, miniaturization, and high reliability. Thus, it is the development direction of manufacturing technology of high reliability and high-voltage transformer, also is an urgent need for the development of UHV power equipment that the pressboard with poor heat resistance, large permittivity is replaced by new polymer materials. The polyphenylene sulfide (PPS) and Polytetrafluoroethylene (PTFE) were chosen for the comparison with paper. They were put in the transformer oil for electrical-thermal aging for 300 days under 90 degrees C, 110 degrees C and 130 degrees C respectively. The trends of power frequency breakdown strength were analyzed combined with the physical properties and electron microscope scanning (SEM) at different stages during aging time. The experiment result shows: as a whole, the breakdown strength of PPS is slightly lower than that of the oil-paper insulation at different aging stages at three aging temperatures, while the breakdown strength of PTFE is higher than that of the oil-paper insulation. At the same time we can see that for these three materials the breakdown strength is not related to aging time, and the breakdown voltage does not fall as the aging temperature rises; the mechanical properties and SEM of polymer material has no clear bearing on its breakdown field strength.