Analysis Of Circulating Current Loss Of Continuous Type Of Winding And Transposition Design In Power Transformer

With the development of domestic economy, the need of electric power is increasingly enlarged. Therefore, the power transformer is being developed into high voltage, large volume transformer. Because of this, the current of the low-voltage side is also largely increased. Its loss, especially the circulating current loss, is becoming more and more concerned. The insulation and duration of transformer is worsened when the circulating current loss is serious. In order to reduce this loss, the transposition is applied. How to seek the best transposition is the key problem for reducing the circulating current loss.The leakage magnetic field of transformer presents a three dimension distribution. If it is calculated through 3D FEM, there exists problems like large number of nodes and huge amount of calculation. To solve this problem, 2D multi-section with less nodes and less computation is applied in this paper. The multi-section method is a directly field-circuit coupling method using FEM to calculate the circulating current losses of continuous type of winding by calculating the leakage magnetic field in transformer through quasi-axisymmetric models constructed by several 2D axisymmetric planes. The multi-section method combined with the direct field-circuit coupled model is proposed for the formulation of the circulating loss calculation.The continuous type of winding is fractional turn disk-shaped winding. Two transpositions are needed for almost each disk. Several supporting bars are involved in every transposition. Therefore, there is a big difference of conductor distribution on each section. In this paper, the distribution of each section is determined, then the circulating current loss is calculated.Because of the effect by the leakage magnetic field of power transformer, there are circulating current losses among conductors connected in parallel in windings. Therefore, the performance of the transformer is worsened by the losses. In this case, the conductors must be transposed in order to minimize the losses. The circulating current losses, the calculation of leakage magnetic field and the transposition optimization have become the key problem in winding design. How to reduce the loss and figure out the optimal transposition are also discussed in this paper. By keeping the transposition unchanged and following some restrictions, the fractional turns are readjusted and the losses are reduced. At last, the designing software of continuous type of winding is programmed so as to calculate the loss and display the curve of flux density. The software is multi-functional and easy to input and output data .Therefore, it can be directly used in practice.