带平衡绕组大电流互感器磁场的三维有限元仿真研究

在大电流互感器(大TA)设计中,由于一次额定电流很大,无法进行现场三相环境条件下的物理试验,故常以等效试验方法来优化平衡绕组的匝数及其各段间的连接方式。但目前的等效试验法不准确,且成本高、周期长,为解决此问题,笔者对以三维有限元法分析现场三相环境条件下大TA磁场的有效性进行了研究。具体采用基于矢量磁位和标量电位的A-Φ法计算了大TA的磁场,采用棱边单元而不是节点单元,避免了用基于矢量磁位的节点单元法计算媒质磁导率不一致的模型时带来的错误,并以间接场路耦合法计及了外电路的影响。计算了在邻相大电流母线磁场干扰下,大TA的四段平衡绕组做反极性串接时,平衡电流值以及铁心中的最大磁感应强度值,并确定了它们随平衡绕组位置改变的变化规律。数值仿真与磁路法估算结果相吻合,证明了以三维有限元法对现场环境条件下大电流互感器的磁场进行仿真是可行的。

3D FEM Computation of Magnetic Field of Heavy Current Transformer with Shielding Coils

In the design of heavy current transformer,equivalent test is widely conducted to optimize the turns and connections of shielding coils.However,this method is not so accurate,and is of high cost and long period for research.Therefore,a 3D FEM(finite element method) computation of magnetic field for heavy current transformer is presented in this paper.The A-Φ method,which is based on magnetic vector potential and electric scalar potential,is adopted to compute the magnetic fields.And the indirect field-circuit coupling approach is used to consider the effect of external circuits.Considering the interference of stray flux from adjacent bus-bar,the maximal magnetic flux density in iron core and the currents in shielding coils are computed,and their variation with position are determined as well.Consistency of the simulation and theoretical results demonstrates that 3D FEM could be used to compute the magnetic field of heavy current transformer,thereby to replace the high-cost equivalent test.