Research On Vibration Of Dry-Type Transformer Core In Fault State

Dry-type transformers are more and more widely used in power systems due to their simple structure,maintenance-free and small footprint.The iron core is one of the main components of the transformer.Once a fault occurs,it will have a serious impact on the operation of the power grid.There is a correlation between the vibration state of transformer core and the fault.The working state of the core can be judged by analyzing the vibration signal of the transformer,and then the operation state of the transformer can be monitored based on the vibration signal,which is of great significance to ensure the safe and stable operation of the transformer.In this paper,the vibration characteristics of transformer under different operation states and core faults are studied by the method of finite element simulation and vibration experiment of transformer.The main contents are as follows:(1)The establishment of magnetic-mechanical coupling model of transformer.The magnetization characteristics and magnetostriction characteristics of the silicon steel sheet used in the transformer under ac excitation were measured with the laser magnetic characteristic test system.On this basis,the magnetic mechanical coupling model of transformer is established to calculate the vibration characteristics of transformer core.(2)Study on vibration characteristics of dry-type transformer under stable voltage operation.The vibration characteristics of the transformer core under different stable voltages(i.e.undervoltage,rated voltage and overvoltage)are calculated respectively.The influence of voltage on transformer vibration was analyzed and the no-load vibration experiment was carried out.It is concluded that the vibration acceleration increases with the increase of voltage,and the correctness of the calculation model is verified.(3)Study on the influence of switching overvoltage on vibration characteristics of dry transformer.By building a circuit to simulate the generation of switching overvoltage(i.e.opening overvoltage and closing overvoltage).Taking this overvoltage signal as the excitation,the magnetic mechanical coupling model of transformer core is used to calculate the vibration characteristics of transformer core when over-voltage fault occurs.(4)Study on vibration of dry transformer core under multi-point earthing and loose faults.This paper analyzes the causes of the multi-point earthing fault of the iron core,and calculates that the multi-point earthing fault will lead to the reduction of vibration acceleration based on the magnetic-mechanical coupling model of the transformer.The influence of the fault on the vibration of the transformer core is obtained through the multi-point ground fault experiment;By analyzing the causes of the transformer core loosing fault,and combining the vibration experiment of the transformer core loosing fault,the change rule of vibration acceleration with time and frequency before and after failure is obtained.It provides theoretical basis and experimental reference for transformer fault diagnosis.