Research On DC Bias Vibration Effect Of Transformer

Geomagnetic induced current(GIC),High Voltage Direct Current(HVDC),and nonlinear power electronic components will make power transformer operate in the AC-DC hybrid environment.DC disturbance will cause the asymmetry of positive and negative half cycle excitation of transformer and produce serious magnetostrictive effect,which will further lead to core saturation,vibration increasing and core loosening.These problems will further reduce the insulation strength of transform,weaken the ability to resist current shock,and even cause damage to transformer and serious accident.This paper relies on Project supported by the National Natural Science Foundation of China(51507027),Jilin Province Science and Technology Development Plan Project(20190303007SF),Jilin Science and Technology Innovation and Development Project(20166014),the identification method of transformer electromagnetic parameters in AC-DC hybrid environment is studied,and the variation characteristics of excitation current and core abnormal vibration under the influence of DC are further explored.In order to study the problem of transformer bias under DC disturbance,a calculation model is established based on the principle of electromagnetic coupling.The applicability of different finite element methods in solving transformer's magnetic field model is studied,and the relevant inductance parameters are calculated based on energy balance principle;the inductance parameters calculated are substituted into circuit model which has considered the influence of DC to further calculate current parameters;the coupling of magnetic field and circuit model is realized according to cyclic iteration principle.Taking three-phase three-limb transformer as example,the simulation model is established by using the finite element software to verify the correctness of magnetic field-circuit coupling calculation method.The DC bias simulation model of single-phase transformer is established,and the variation characteristics of inductance parameters,core magnetic field and transformer leakage magnetic field are analyzed.It is found that the saturation degree of the transformer excitation will deepen with the increase of DC level,along with the increase of the magnetic induction intensity of the core and the leakage flux around the core.Aiming at the problem of transformer core vibration,the harmonic response analysis model of excitation-vibration in AC-DC hybrid environment is established to simulate the electromagnetic characteristics of transformer under different DC disturbance levels.The saturation degree of excitation is characterized by the waveform distortion degree of excitation current.The time-harmonic characteristics of excitation current and vibration acceleration are analyzed,and the corresponding relationship between them and excitation state is dug in depth.For 380V three-phase three limb Y/? transformer,a modular dynamic model experiment platform is established-The excitation current identification module and vibration monitoring module are used to identify and collect excitation current and core vibration signals.The experimental data are compared with simulation results to verify the validity and correctness of the proposed method.It is found that under the influence of DC component,the excitation current presents the characteristics of "half wave distortion and half wave attenuation".Meanwhile,the vibration of the core is intensified,and the amplitude of the vibration spectrum is increased with the largest change at 100Hz.The abnormal winding current under DC disturbance is studied to characterize core vibration.Taking three-phase group transformer and three-phase three-limb transformer with the same capacity and voltage ratio as research object,the simulation calculation is carried out for the transformer in different operation modes under different DC disturbances,and the electromagnetic characteristics are studied.The variation characteristics of winding abnormal current and core vibration acceleration under the influence of DC are analyzed,and its rule is summarized.The simulation results are verified by building experimental platform,and the DC disturbance resistance ability of group transformer and limb-transformer is further compared.The criterion of vibration characterization based on abnormal current is established.It is found that the core vibration can be characterized by the change of no-load current,and the anti-DC disturbance ability of three-phase group transformer is better than that of three-phase three-limb transformer.