| The Inverted-Type Oil-Immersed Current Transformer(IOCT)in the traction substation along the high-speed railway is an important electric equipment to ensure the safe operation of the railway power supply system.However,the IOCT main insulation deflagration accident along the Lanxin high-speed railway in 2015 indicates that the oil-paper insulation system located at the head of the IOCT will be seriously deteriorated under the influence of harsh environment in the west region,resulting in a severe decline in its insulation performance.Therefore,the aging research and life assessment under the complicated conditions of the oil-paper insulation system have important theoretical and engineering significance for the safe operation of IOCT.Considering that IOCT is affected by the frequent short-time pulse of high-speed trains,as well as the natural conditions such as large temperature difference and frequent changes in temperature and humidity in the west region,this thesis selects three stresses of temperature,humidity and short-time impulse voltage for testing the aging state of oil-paper insulation system with aging time under laboratory.The degree of polymerization and dielectric parameters are used as the aging characteristic parameters,and a mathematical model of life evaluation is established based on the aging mechanism of oil-paper insulation.Main tasks as follows:(1)Comprehensive research on the aging mechanism of oil-paper insulation is carried out in domestic and foreign references,and the effects of temperature,moisture,voltage and oxygen on the insulation life of oil-paper are analyzed.Combining the cumulative kinetic model of fiber polymerization degree with the aging mechanism,the oil-paper insulation aging model is initially established.Afterwards,the model is extrapolated to the operating condition based on the principle of time-temperature superposition,so that is has engineering practical significance.(2)Accelerated aging test of oil-paper insulation under laboratory conditions.The degree of polymerization and dielectric parameters of oil-paper insulation samples with different temperature,moisture and unequal times of short-time impulse voltage accumulations in unequal aging time and frequency are measured separately.The polymerization degree curve and frequency domain dielectric spectrum under complex aging conditions are plotted,and the aging mechanism is combined to analyze the curve variation law under different aging conditions.(3)Based on experimental data,the cumulative loss rate of polymerization degree is plotted with aging time.Using the coordinate translation method to obtain the main curve of the polymerization degree of oil-paper insulation varying with the aging time under the superposition of arbitrary temperature,moisture and short-term impulse voltage.Combining the above life assessment model which is based on the aging mechanism to quantify the relationship between each stress correction coefficient and stress levels.At last,a life assessment model of oil-paper insulation under complex conditions is established,which not only conforms to the aging mechanism of oil-paper insulation and the rule of test data,but also can be applied to the actual engineering conditions. |
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