Study Of Core Vibration In Power Transformers

Power transformers in normal operation of the structure will be subjected to the role of forces and thus produce vibration,this vibration have an impact on the structural strength of the transformer,so that the structural parts looseness reduce the life and strength of structural parts.The vibration generated by the operation of the power transformer includes the vibration generated by the transformer itself by the action of the alternating electromagnetic field by the action of the force and the vibration generated by the transformer oil,oil pump,cooling fan working conditions,of which,the vibration of the power transformer core accounts for the largest proportion.The core joints and the size of the clamping force of the structural parts can have an impact on the local vibration of the transformer core,the thickness of the silicon steel sheet material,the silicon steel sheet cold and hot rolling process,the design flux density and other characteristics also affect the vibration of the transformer body.The vibration of the transformer core is due to the electromagnetic and magnetostrictive forces,of which magnetostriction is the dominant influence on the vibration of the transformer core.The hysteresis of a transformer core is caused by the hysteresis effect of a silicon steel sheet subjected to an alternating magnetic field.In order to analyse the hysteresis effect of a silicon steel sheet,a mathematical model can be developed that can completely describe the hysteresis effect of a ferromagnetic material and can simulate the complete hysteresis line.However,there is no mathematical model that can describe the hysteresis effect and simulate the butterfly curve.Therefore,the use of a mathematical model that can completely describe the magnetostrictive effect and simulate the butterfly curve is of great theoretical importance and research value.This paper proposes a Preisach model to describe the magnetostrictive effect based on the classical Preisach model,followed by the measurement and analysis of the electromagnetic and magnetostrictive properties of electrical silicon steel sheets,then a simulation study on the vibration of power transformer cores,and finally an experimental study on the vibration of the simulated power transformer cores.The main studies are as follows.Firstly,the basic concept of the mathematical model of hysteresis is described from the principle of hysteresis of ferromagnetic materials.Then,by deriving the classical Preisach model and Mayergoyz’s non-linear Preisach model,a mathematical model capable of describing the magnetostrictive properties of a single silicon steel sheet is obtained.Next,the electromagnetic and magnetostrictive properties of the silicon steel sheet are measured at different angles and under different excitation conditions.The B-H curve and the butterfly curve of the silicon steel sheet under different conditions are given and analysed,and it is suggested that the higher vibration at the joints of the transformer core may be closely related to the angular change of the magnetic circuit at the joints.Finally,finite element simulations are carried out for a 160 k VA single-phase four-column power transformer,and magnetic density distribution and vibration displacement clouds are given.Experimental analysis of the transformer is also carried out,and vibration displacement and vibration velocity are measured at 16 measurement points,including the upper yoke and side yoke,and the experimental results are analysed.