| Overheating fault is one of the two major faults in the oil filled equipment such as transformer.So the study of overheating fault in oil filled equipment,can not only discover the thermal fault of oil filled equipment,can also avoid the conversion from thermal fault to electricity fault in time,to reduce the incidence of fault in oil filled equipment on the whole.In oil-immersed transformer,for example,maximum temperature of fault in the internal oil-paper insulation structure is above 1000℃.Energy released by thermal fault point will damage chemical bonds in transformer oil molecules,causing decomposition of big hydrocarbons to low hydrocarbons molecules gas and hydrogen gas which will dissolve in transformer oil.From mineral oil pyrolysis mechanism under thermal fault and experimental simulation two aspects,this paper,first of all,used the reactive molecular dynamics simulation method to study the law of the pyrolysis process of the mineral oil and the law of gas generation,and then,thermal fault was developed under the experimental model.And by the way,experimental research of mineral oil decomposition was developed to provide the theoretical foundation for fault diagnosis,such as fault type and the severity of fault.In this paper,main work is as follows:(1)Based on ReaxFF(reactive force field),in this paper,the reactive molecular dynamics(MD)simulation method was used to establish the simulation model of mineral insulating oil molecules under different temperatures and to study dynamic pyrolysis process and produce regularity of gaseous molecules in mineral insulating oil.Through the dynamic images in the simulation process and the analysis for the pyrolysis products of mineral insulating oil under different temperatures and time by a Reactive-MD-analysis model,the microcosmic reaction process of insulating oil was analyzed,and the pyrolysis reaction path and the production path of small molecules were concluded.(2)Focus was fixed on the effect of temperature and time on the micro process and the energy change in the pyrolysis process.By comparisons with the improved three ratio method and the TG-DSC test in different ways,this paper proved the rationality of the simulation results.And Reax FF molecular dynamics simulation provided an effective way to study the pyrolysis of the mineral insulating oil.(3)Developed a thermal fault simulator of oil filled equipment such as transformer.Based on the transformer entity model mainly transformer device,the simulation is mainly consist of heating element,box,temperature control module,temperature measurement module,gas measurement module,and power measuring module.It can ensure the precision of temperature control through voltage regulation power,realize the all-round real-time measurement of temperature through temperature sensor with many roads,and achieve energy measurement through the power of control.Through finite element simulation software COMSOL the temperature field under the thermal fault inside the device was simulated,and comparison with the temperature field in the actual transformer,the rationality and reliability of the simulating experiment device was verified,so as to realize simulation of emergence and development process of thermal fault.(4)The temperature field distribution and the rule of the gases during the development process of the thermal fault in the device were studied.Through the measurement of temperature field and the observation of gases generation in the heating process,temperature field distribution and the rules of gases generation were studied with the change of surface temperature,heating time,power of heating element and energy generated by the heat source.And then the impact of temperature,time,power and energy had on pyrolysis of mineral insulating oil were analyzed.The research of pyrolysis mechanism and decomposition simulation experiment device of mineral insulating oil under the thermal fault provided a theoretical basis for thermal fault diagnosis. |
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