Combined Electrical and Thermal Aging of Alumina Filled Epoxy Solid Insulators for GIS

Abstract

Gas insulated switchgear (GIS) is increasingly developing toward high voltage and large capacity. During the operation of GIS, the epoxy insulation components gradually age due to multiple issues of electricity, heat, and various environmental factors. Insulator aging reduces the electrical strength and mechanical strength of insulators and further leads to GIS failure, therefore it becomes a crucial issue for GIS with long running time, which determines the operating life of GIS. Thus, life assessment is an important work to ensure the safety and reliability of GIS. In this work, through the aging breakdown life time of insulators under different electric fields and temperatures, the parameters of the aging model are obtained, and a simple phenomenological life model is proposed based on the consideration of voltage and temperature. The thermal characterization results show that glass transition temperatures of the epoxy samples are in the range between 105°C to 125°C. All the samples are treated under the electrical conditions of applying electric field intensity of 23, 26 and, 29 kVrms/mm and simultaneously coupled with a heat treatment under a temperature of 30°C, 105°C, and 130°C, respectively. To deliver the tests, a multi-specimen high voltage test device is set up, which combines the possibility of testing 10 samples simultaneously under the combined action of voltage and temperature. Breakdown lifetime values under different combinations of voltage and temperature conditions are measured based on the above platform. Furthermore, a preliminary phenomenological life model is proposed based on a suitable choice of the stress function e.g. that takes into account of voltage and temperature. The experimental results show that with the increase of aging time, the cumulative failure probability of GIS cylindrical insulation specimen increases. The electrical and thermal aging phase greatly accelerates the aging time, and a certain regularity compared with the electrical aging is presented.