Research On Key Micro-mechanism Of Pyrolysis Process Of Oil-paper Insulation In Power Transformer

As the key equipment for voltage regulation, power transmission and power distribution, power transformer plays an indispensible role in the safe, reliable and stable operation of power system. Once an accident happens, it may cause huge economic losses and even results in severe social impacts. Therefore, an incisive understanding of the decomposition mechanism of transformer insulating material as well as effective diagnosis and evaluation of potential failures presents both theoretical and practical significance in reducing failure risk and ensuring reliable operation of the power grid.On the basis of comprehensive understanding of the oversea and domestic research status of the decomposition mechanism of oil-paper insulation in power transformers, the micro-mechanism of the pyrolysis process of oil-paper insulation is intensively studied in this paper by introducing the thermodynamics theory and molecular simulation technology, in order to reveal the connection between the microscopic changes and the macroscopic properties of the insulating material, and to explore the new indicators of characterizing the severity of transformer failure. The innovative achievements obtained in this paper mainly include:(1) By introducing the enthalpy change of thermodynamics theory, this paper aquired the formation energy for each DGA fault gas through calculating the enthalpy change values of the representative chemical reactions for generating gases in transformer insulating material. A new criterion is built to assess the overheating fault severity of power transformer from the perspective of energy state.(2) The bond-order based ReaxFF was adopted in molecular simulation to investigate the micro dynamic mechanism of the pyrolysis of insulating material, including mineral oil and vegetable oil, in power transfomers. By analyzing the simulation trajectory files of the pyrolysis of transformer oil with the element tracking method, this paper tried to sort out the initial decomposition mechanism, the difference in main products of different oil as well as the evolution mechanism of the main products. Through calculating the reaction enthalpy in the process of pyrolysis, the correlativity between distributions of the pyrolysis products over time and the reaction enthalpy was built, and the energy changing law during the pyrolysis is also revealed.(3) By introducing ReaxFF-based molecular simulation technology and py-GC/MS based chemical analysis technology, this paper carried out both analogue simulation and experimental research on cellulose under high temperature, in order to investigate the microscopic mechanism in the process of cellulose pyrolysis. Through the theoretical and experimental verification, this paper sorted out the initial decomposition mechanism and the evolution mechanism of main products during the cellulose pyrolysis process. Meawhile, this paper tend to provide micro-characteristic parameters for fault diagnosis by studying the dynamic mechanism of cellulose pyrolysis at atomistic level.