Research On Oil-immersed Transformer Winding Overheat Warning And Insulation Thermal Aging Evaluation

As the core equipment of the power supply system,the oil-immersed transformer undertakes the tasks of voltage conversion and energy transmission,and its operational reliability is related to the stability of the entire power supply system.Winding insulation is the key part of the transformer.Once the winding overheats,it will cause the local temperature to be too high,which will seriously accelerate the thermal aging rate of the winding insulation,which will lead to the destruction of the insulation performance and even the failure of the transformer.Therefore,how to pre-warn the overheating of the winding fault and evaluate the aging state of the winding insulation is a key research issue.In this paper,based on the heat transfer of the oil-immersed transformer and the flow characteristics of the internal fluid,a three-dimensional numerical model of the transformer is established to simulate the breathing process under the condition of winding overheating.This paper studies the influence of load factor and ambient temperature on the respiration of the transformer,and focuses on the changing trend of the breathing process under different loads and different ambient temperatures.In this paper,the characteristics of respiration changes of winding overheating and normal overheating are compared and analyzed,and the characteristic parameters that can characterize the overheating of the fault are extracted.According to the support vector machine model,a warning method for overheating of transformer winding faults based on breathing parameter monitoring is proposed.In order to solve the problem of deterioration of the winding insulation state caused by thermal aging,this paper prepared insulating papers with different aging states in the laboratory through accelerated thermal aging experiments,respectively tested the degree of polymerization of the insulating paper,and analyzed the change of polymerization degree with aging time.In this paper,the transformer winding insulation model is designed and built.The frequency domain dielectric spectrum test is performed on the winding models under different aging conditions,and the frequency domain dielectric spectrum characteristics of the winding insulation during uniform aging and non-uniform aging are studied.According to the frequency domain dielectric spectrum test results of winding insulation under different aging conditions,an equivalent circuit model for analyzing winding insulation is constructed in this paper.Based on the Dissado-Hill dielectric response model,the frequency domain dielectric spectrum is analyzed.In this paper,the variation trends of different model parameters and aging time are analyzed,and the extracted frequency insulation feature characteristics of the winding insulation are studied.In this paper,it is found that there is a good correlation between the characteristic parameters and the aging time,and an evaluation method of the transformer winding insulation aging state is proposed and verified.