Investigation On Decomposition Characteristics Of Nomex Insulation Paper In The Mining Dry Type Transformer During Hygrothermal Aging

This thesis is one of the important contents of the National Natural Science Foundation of China “Nomex insulation aging mechanism for mining dry type transformer”(51577123).It is mainly proposed to investigate the decomposition characteristics of Nomex insulation during the thermal degradation process of insulation aging.Mining dry type transformer has replaced oil-immersed transformer to become the key equipment of power supply system in underground coal mine.The state of transformer insulation structure directly determines the safety and stability of power supply system.Due to its excellent electrical and mechanical properties,Nomex insulation paper is widely used in mining dry type transformer insulation structures.However,the underground environment is bad,the insulation system of transformer is affected by heat,electricity,acid,oxygen,moisture and other factors for a long time,resulting in the insulation paper aging and the decline of its electrical and mechanical properties.Hydrolysis is the main form of insulation aging.Therefore,it can lay a theoretical foundation for the state assessment,life analysis and fault diagnosis technology of transformer by exploring the variation law of polymerization degree and pyrolysis characteristics of Nomex insulation paper of mining dry type transformer in the aging process.At present,scholars at home and abroad focus on the study of oil-immersed transformer insulation paper,especially the study of its degradation characteristics has established a relatively complete theoretical system.However,there are few reports on the dynamic characteristics of Nomex insulation paper for mining dry type transformer.The accelerated hygrothermal aging test on Nomex T410 was carried out in this paper.The polymerization degree of insulation specimens under different aging conditions was measured,and the influence of temperature and moisture on the polymerization degree was analyzed.In addition,the thermal gravimetric analysis and differential thermal analysis were carried out by synchronous thermal analyzer,and the variation law of dynamic parameters of insulation paper with different aging degree was investigated.Specific research contents are as follows:This paper designs the Nomex insulation paper wet heat aging test program,builds an aging test platform based on the structure of the insulation system,and combines the actual operation of the mine dry-type transformer in the underground,formulates the wet heat aging technical route.The current status and multiple tests have determined the Nomex insulation paper wet heat aging test parameters.In this paper,through the hygrothermal aging test system,accelerated hygrothermal aging test was carried out on the Nomex insulation paper with thickness of 0.05 mm under the conditions of temperature of 160?,180?,200? and initial moisture content of 3%,5% and 7%,respectively.The aging stress factor intensity was determined by referring to the IEC60811 standard and the research status at home and abroad.The degree of polymerization is the most favorable criterion for characterizing the mechanical properties of Nomex insulation paper at home and abroad.The intrinsic viscosity of Nomex insulating paper under different aging conditions was measured with a viscometer while maintaining a constant temperature water bath at 30?,and the degree of polymerization was calculated.The effects of aging time,temperature and initial moisture content on the aging of Nomex insulating paper were analyzed.Studies have shown that both the initial moisture content and temperature will accelerate the aging of Nomex insulation paper.Under the effect of moisture,the temperature is more sensitive to the aging performance of Nomex insulation paper.In this paper,through the synchronous thermal analyzer,accelerated hygrothermal aging test TG,DTG and DSC curves of Nomex insulation paper were measured under different aging conditions.The variation law of characteristic value of insulation paper pyrolysis in different aging states was analyzed,the thermal cracking kinetic parameters of insulation paper were calculated and extracted according to the TG curve,and the variation law of activation energy of insulation paper was analyzed with the deepening of aging degree.The results showed that the initial decomposition temperature of insulation paper gradually moved to the direction of low temperature with the deepening of the aging degree,the maximum reaction rate gradually decreased,and the residual mass of the sample showed an increasing trend after the reaction.In the whole aging process,the activation energy increased first and then decreased with the decrease of polymerization degree.To some extent,it provides a theoretical basis for the condition evaluation and aging mechanism research of Nomex insulation paper for mining dry-type transformers.