接头电阻对CORC电缆交流损耗的影响分析

Analysis of the Influence of Joint Resistance on AC Loss of CORC Cable

采用第二代高温超导(HTS)带材绕制的CORC电缆具有载流能力高、力学性能好等优点,是制造核聚变磁体的理想电缆之一。然而,当由CORC电缆制造的核聚变磁体闭环运行时,现有的工艺很难保证每根CORC电缆的超导带材的接头电阻完全相同,这会对CORC电缆的交流损耗等电气特性产生重要影响。因此,该文搭建了含接头电阻的CORC电缆的三维有限元模型,分析了接头电阻对CORC电缆交流损耗的影响。结果表明,当CORC电缆传输交流电流时,不均匀的接头电阻将导致CORC电缆三根超导带的电流分布不均匀,进而增加了电缆的总体交流损耗。此外,得到了CORC电缆的交流损耗总是随着接头电阻不均匀程度的增加而增大的分析结果。

The conductor on round core(CORC)cable,spirally wound by high temperature superconducting tapes,will generate AC loss,which increases the heat burden and even endangers the safe operation of the entire superconducting system.In practical applications,joint resistances will inevitably appear in the joints of CORC cable.However,the existing technology is difficult to ensure that the joint resistance of each superconducting tape of the CORC cable be exactly same.The differences of joint resistance will have significant impacts on the AC loss of the CORC cable.Therefore,a 3D finite element model of CORC cable with joint resistance is established,and studies on the influence of joint resistances on AC loss of CORC cable is carries out.A CORC cable based on finite element software is built.Firstly,a small segment is cut at the end of each superconducting tape of CORC cable to simulate the joint resistance,and the geometric model and equivalent circuit model of the CORC cable are constructed.Secondly,it is meshed and optimized.Finally,the Maxwell Equations are solved based on H-formulation.The model can accurately and effectively simulate the influence of joint resistances on the electrical characteristics of CORC cable.The simulation results show that when the transport DC current is applied to the CORC cable with no joint resistance,the transport DC current is evenly distributed to the three superconducting tapes.When the ratio of the joint resistances of the three superconducting tapes is R_(t1):R_(t2):R_(t3)=1:2:3,the ratio of the DC transport current through the superconducting tapes is I_(1):I_(2):I_(3)=6:3:2,which verifies the accuracy of the model.When the AC transport current is applied to the CORC cable,the transport current of the three superconducting tapes is not distributed according to the ratio of the joint resistances,and the phase of the AC transport current in each superconducting tape is also different.The following conclusions can be drawn from the simulation analysis:(1)Uneven joint resistances of the CORC cable directly leads to the inconsistency of the transport current of each superconducting tape.When the DC current is transported,the current distribution of each superconducting tape is mainly affected by the joint resistances.When the AC current is transported,the superconducting tapes have reactance due to their spiral winding structure,so the current distribution and phase of each superconducting tape are affected by the reactance and the joint resistance of the superconducting tape.(2)Due to the joint resistance and reactance of the superconducting tape,when the CORC cable transports AC current,part of the AC current will flow into the former and cause loss.Compared with the AC loss generated by the superconducting tapes,the loss generated by the former accounts for a larger proportion of the total loss of the CORC cable.(3)When the AC current is transported,the AC loss of the CORC cable with even joint resistances is always smaller than that of the CORC cable with uneven joint resistances.The total AC loss of the CORC cable is always positively correlated with the uneven degree of the joint resistances.When the joint resistance distribution type of the superconducting tapes is Large-Large-Small,the AC loss of the CORC cable is most obviously affected by uneven degree of the joint resistances.