Simulation Study Of Converter Transformer Magnetic Shield On Electromagnetic Performance Effect

Converter transformer plays an important role in HVDC transmission system.Due to the dual function of AC voltage and DC voltage in converter operation,the load current contains a large number of high harmonic components.Therefore,the calculation of its winding leakage magnetic field and related performance parameters is more complicated than general power transformer,the problem of additional loss and local overheating in winding and structural parts is always a key issue in transformer production and operation department.In this context,the paper firstly carries on the simulation and verification analysis of the stray losses of P21-B and P21-a in the international benchmark model,the calculation method of steel plate with surface impedance equivalent and non-magnetic steel open three slots is determined.Then,the eddy current loss of a converter transformer is calculated by using secondary development calculation software,the reliability of software result is verified by comparing the result of MF2 D.On the basis of the determined method,the structural characteristics of converter transformer for Siemens structure are analyzed and the reasonable three-dimensional computing model is established.The winding leakage magnetic field,short circuit impedance and additional loss for converter transformer are calculated and influence of harmonic current is also analyzed by the combination of numerical and analytical method.It not only proves the correctness of calculation method,but also provides basis for the improvement and optimization of shield structure for converter transformer.Finally,the original shielding system is improved and the lobe type magnetic shield is installed in the body press on the basis of distribution of leakage flux and additional losses for converter transformer.Changes of the leakage magnetic field,short circuit impedance and additional losses of former and backward are compared and analyzed.To further improve the effect of composite shield structure and meet the need of optimal structure design for converter transformer,the influence of the thickness,geometric position and other factors on the performance of the transformer wingding and structural components are also investigated.It is shown by calculating results that lobe type magnetic shield can improve leakage magnetic field distribution of winding ends and reduce stray losseffectively,a number of useful suggestions are given for design of converter transformers.