超导变压器几种不同绕组形式的环流分析

Study of Circulating Current Distributions for Different Types of HTS Transformer Windings

由于超导材料的零电阻特性,绕组各支路或并绕导线间漏电抗小小的不平衡将会引起很大的环流。环流的存在使得磁场分布更不均匀,进而影响交流损耗和临界电流。本文采用磁场计算与电路分析相结合的方法,即在用有限元法分析磁场并计算反映支路间电磁耦合的电感矩阵的基础上列写电路方程,计算了低压绕组取圆筒式、螺旋式和饼式等三种形式8种情形的环流,并分析了支路电阻对环流的影响。结果表明,仅从减小环流看,圆筒式绕组较螺旋式和饼式绕组更适合具有多根导线并绕的情况;而从减小环流和减少导线焊点考虑,双螺旋式绕组具有优势。同时还证明就环流来说,不能将二次侧圆筒式绕组各层两端短接后用铜线过渡到相邻层来代替绕组轴向并绕导线在层间的换位。

In a high temperature superconducting (HTS) transformer a slight unbalance of the branch inductances of the windings might result in heavy circulating current because of zero resistance of HTS tapes. It is well-known that the circulating current worsens the distribution of leakage magnetic filed and consequently does harm to the ac loss and critical current in the tapes. In this paper, the influence of the secondary winding configurations on the circulating current is studied by the method of combining magnetic field calculation with circuit analysis. In terms of reducing the circulating current, the analysis shows that a cylindrical winding has an advantage over a helical winding or a pancake winding if more than one tape is required in parallel for heavy current. If, however, both the circulating current and the manufacture techniques are considered simultaneously, a helical winding is excellent.