Core Material Modeling And Prototype Development For The Power Transformer With The Function Of DC Bias Suppression

In recent years，DC bias, caused by DC grid and geomagnetic storm, makes the powertransformer a series of problems like iron core saturation. The normal operation of the powertransformer and the AC power grid has been influenced by DC bias. Most of the existingmethods for DC bias suppression can suppress the DC bias effectively, but the methods lead tounsafely ground connection of the power transformer. So the new type power transformer withthe function of DC bias suppression is put forward by the existing research. The new typepower transformer can suppress the DC bias by itself automatically and connect ground safely.Firstly, hystersis model of compensation core in the new type power transformer isestablished based on Preisach model theory. Compensation core is consisted of the two-phasemagnetic material. Hysteresis loop of the two-phase magnetic material is tested by experiment.Magnetization curve and reverse magnetization curve are calculated, and relationship betweenremanence of compensation core and motivation. In addition, The hysteresis model of nanotwo-phase magnetic material is established based on micromagnetic theory. The relationship ofthe soft magntosphere thickness and the hysteresis characteristic is obtained.Secondly, stucture of the new type transformer is designed. Compensation core ismagnetized and offsets the flux from DC bias, in the DC bias situation. Compensation corewithout remanence did not influence the transformer in the situation without DC bias.Hysteresisi characteristic of electrical steel sheet is tested. Simulation of the new type powertransformer is finished, which verifies the feasibility of the new type power transformerstructure.Thirdly, the two-dimensional field-circuit coupling model of the new type powertrasformer is established for simulation. Excitation current, iron loss and distribution ofmagnetic density are calculated before and after suppression in different situations. Thecontrast of excitation current, iron loss and distribution before and after suppression verifiesthe suppression effect of the new type power transformer.Fourthly, the prototype of1kVA newtype power transformer is made and tested.Excitation current and harmonic are measured before and after suppression in differentsituation. The contrast of excitation current, harmonic component and harmonic distortion rate verifies the suppression effect of the new type power transformer.Results of simulation and experiment indicate that after suppression of DC bias oddharmonic of excitation current, harmonic distortion rate, magnetic flux density and iron lossdecrease, which verify that the new type power transformer with the function of DC biassuppression can suppress the DC bias automatically, by structure optimization itself, and laythe foundation for further research of DC bias problem.