314 / 2018-09-26 00:13:53

Ageing and Lifetime Evaluation of Epoxy Insulator for GIS under the Multifactor Stresses Effect

GIS Epoxy Insulator,Multifactor stresses,Lifetime evaluation,Ageing

Gas insulated switchgear (GIS) is becoming more and more inclined to high voltage and large capacity development. During the operation of gas insulated fully enclosed composite electrical appliances, the GIS epoxy insulators will gradually be aging under the combined action of electricity, heat, mechanical vibration and various environmental factors. Insulation aging reduces the electrical strength and mechanical strength of insulators, and even leads to GIS failure. For GIS with long running time, insulation aging problem is more prominent, and its life largely depends on the life of insulators, so life assessment is an important condition to ensure the safe and reliable operation of GIS.

This paper first introduces the electrical, thermal and mechanical joint aging test platform of GIS column insulation test parts, including column insulation test parts, power frequency transformers, high temperature oven, mechanical vibration excitation device and accumulative timing device. Secondly, the pressure test and joint aging test of cylindrical insulation specimens with 2 mm spacing are carried out. In order to study the internal condition of GIS interval, we use power frequency voltage to test the change of insulation aging characteristics after long-term operation. And in order to accelerate the aging test, the voltage of 300 Hz frequency is choose to shorten the aging time. This paper is based on an investigation made by applying high voltage aging test on solid epoxy insulator under different voltage temperature and mechanical stress and effect of breakdown are monitored. It is necessary to measure glass transition temperature, capacitance and dielectric loss for analyzing the change of material characteristic. Fourier infrared analysis is also used to analyze the insulating performance change after aging for some time. The result of Fourier infrared analysis shows that the material changes, which causes insulation aging and both mechanical strength and electrical strength lower. For this purpose, a research has been carried out on GIS epoxy insulator in Shandong Taikai high voltage switch company. The aging of insulating material is considered as a direct factor resulting in switchgear insulation. The epoxy resin shows its glass transition temperature in the range between 105°C and 125°C. Furthermore, under the electrical conditions of applying voltage of 40 to 52 kVrms, respectively and for each voltage the temperature was applied, e.g. 130°C, 140°C, and 150°C. In this research a multi-specimen high voltage test setup which combines the possibility of testing 10 samples simultaneously under the combined action of voltage temperature and mechanical stress. The Experiment gives breakdown values at different combinations of voltage temperature and mechanical stresses.

In this paper, a simple phenomenological life model is proposed based on a suitable choice of the stress function, e.g. that considers of voltage, temperature, and mechanical vibration. The experimental results show that with the increase of aging time, the cumulative failure probability of GIS cylindrical insulation specimens will increase. In the experiment of electric, heat and mechanical stress combined aging, it is found that the electric thermal mechanical aging phase greatly accelerates the aging time and presents a certain regularity compared with the electrical aging.