Epoxy systems for low temperature applications
Epoxy-based formulated products are finding increased utility in a wide variety of structural and electrical applications that are required to operate in low temperature environments. Cryogenic technology is accelerating the growth in these fields. This versatile thermosetting polymer offers many attractive features such as high mechanical strength, outstanding dielectric characteristics, excellent adhesive properties, very good chemical resistance and excellent thermal endurance. Such features make them materials of choice for high and medium voltage electrical apparatus that operate in below zero Celsius environments. At lower operating temperatures, many factors come into play affecting overall performance. Among these factors are: speed and effectiveness of cure, fracture toughness characteristics, and thermal expansion properties.
Electrical aging tests on epoxy insulators in GIS
Due to the relatively small insulator dimensions in gas-insulated switchgear (GIS), the electrical stressing is high by comparison to that of insulators for conventional switchgear. Aging tests on a large number of full-sized insulators in several vessels in an outdoor test station have been carried out to determine the stress limits. The tests, with voltages of several hundred kilovolts, last for several years. The aim is to work out conditions (by extrapolation) for a trouble-free switchgear operating life of at least 50 years. The most important test objects are postinsulators weighing 2 kg each. It has been confirmed that partial discharges have a major effect on the failure probability. The life curve obtained from the test results of six batches of partial-discharge-free insulators is compared with the required reliability data. >
Molecular weight distributions in epoxy resins
An exact procedure for calculating the weight-average and number-average molecular weights of epoxy resins made by the advancement process is presented. The calculation can take into account the presence of high molecular weight diepoxides and monofunctional epoxides in diglycidyl ether of disphenol A and indicates that the presence of the latter has a very significant effect. A model for the taffy process based on the overall reactions of the process was developed. Analytical solutions could be obtained if the dehydrohalogenation reactions were assumed to be fast. The predictions of the model are in good agreement with the observed values reported earlier.