Vibration Characteristics Of The Inductive Filtering Converter Transformer

HVDC transmission system has obvious advantages in long distance transmission and network interconnection.It has been developed rapidly in the power system.In HVDC transmission,due to the nonlinear characteristics of the converter components,the converter is a harmonic source which causes power quality pollution for the power grid.And,the converter transformer bears the influences of harmonic currents in windings and harmonic magnetic fluxes in iron cores.The electromagnetic vibration of the windings and the magnetostriction of the cores are intensified.The ability of anti-short-circuit of converter transformer is weakened.At the same time,the noise radiated by the converter transformer seriously affects the living and working environment of the surrounding residents.Combined with the development of HVDC transmission and converter transformer.A new type of converter transformer based on the principle of inductive filtering technology is introduced in detail.Take its principle prototype as the object of study.In this paper,the vibration characteristics of the inductive filtering converter transformer are studied.The main research works are as follows:(1)The principle of the inductive filtering technology is expounded and the impedance condition to realize the inductive filtering technology is analyzed.The HVDC transmission model based on the inductive filtering converter transformer is established.The test results show that the inductive filtering technology has an excellent inhibitory effect on the harmonic currents and the harmonic fluxes.It provides a theoretical basis for the research that the inductive filtering technology can effectively suppress the vibration of transformer.(2)According to the principle of simplification,taking the winding as the research object.Modal analysis is carried out,the modal frequencies and modal shapes are obtained.In actual operation,the material parameters which affect the modal analysis results of winding are random.The traditional deterministic finite element analysis ignores their randomness.The randomness of these input variables is considered in this paper.Monte Carlo simulation is applied to get the statistical parameters of the modal frequencies of winding.The scatter grams and probabilistic sensitivity analyses between the modal frequencies and the random input variables are obtained.From the perspective of structural resonance,the modal frequencies of the winding are analyzed.(3)The finite element model of transformer core is established.The modal frequencies and the corresponding mode shapes are obtained by modal simulation.Considering the uncertainties of material parameters and clamp forces,a sample set of the input variables is got by using of the central composite design method.The response surface model is chosen to establish the function expressions between modal frequencies and input variables,these function expressions are used as a surrogates of the modal frequency simulation results of the core.Monte-Carlo method is used to obtain the statistical parameters of the modal frequencies.The response surface diagrams corresponding to the modal frequencies are given.The fitting accuracies of the response surface models are evaluated by the variance analysis.(4)The problems of vibration and noise of converter transformer are more serious than that of power transformer when the capacities are the same.The main reason is that the converter transformer bears the harmonic currents generated by the converter,as well as the influence of harmonic fluxes in the core.The inductive filtering technology can suppress the harmonic fluxes in transformer core and the harmonic currents in line side winding,so that running vibration of the converter transformer is suppressed at the source.The experimental platform for the vibration test of the inductive filtering converter transformer is established.Through the vibration tests under load,the test results verify this theory.The vibration spectrums are analyzed from the view of structural resonance.(5)In HVDC transmission,when HVDC system operates in monopolar mode and uses the earth as a return path,as well as the neutral potential caused by geomagnetic storm is rised.They will cause the DC bias phenomenon of the converter transformer.In order to simulate this phenomenon,in the 6-pulse rectifier bridge,by controlling conduction angles of some thyristors are different from that of the other thyristors to form an equivalent DC current,and a DC magnetic flux is formed in the transformer core.The tests of vibration and noise for the inductive filtering converter transformer under DC bias are conducted.The results also show that the inductive filtering technology can control the vibration and noise at the source.The vibration characteristic of the inductive filtering converter transformer is a complex problem.In this paper,the inherent modal characteristics of the prototype and influences of the inductive filtering technology on the vibration of converter transformer are studied.Considering the transformer in operation,the material parameters of components are aging,etc.The uncertain finite element modal analysis is carried out.More comprehensive modal simulation results are obtained.The related tests under load and DC bias are carried out for the prototype.The test results show that the inductive filtering technology can reduce the vibration and noise of the converter transformer at the source.It lays the foundation for the engineering application of this new type of converter transformer.