电气化隧道中的导线—地回路阻抗

Impedance of Conductor-earth Circuits in Electric Railway Tunnel

在电力系统,特别是在电气化铁道中,会遇到导线架设在隧道中的情况,过去一直采用Carson公式计算隧道中导线的阻抗,但采用Carson公式计算隧道中导线–地回路阻抗存在固有模型误差。在比较半无限平面大地模型和四周无限大地圆形隧道模型基础上,提出电气上的长大隧道概念。结合电气化铁道隧道实例,进行对比计算,给出Carson公式所导致的误差。结果表明阻抗误差随频率的增高而增大,随大地电阻率的增大而减小,即使在工频下仍超过5%。进而从物理概念上分析两种模型的差别,讨论在长大隧道中采用Tylavsky公式的合理性。

In power systems, especially in electric railways, sometimes conductors are suspended in tunnels. Carson formulas have been used to compute the impedance of conductors in a tunnel in the past. However, there exists an inherent modeling error when using Carson formulas to calculate the impedance of conductor-earth circuits in a tunnel. Based on model comparison between the semi-infinite earth and the circular tunnel with peripheral infinite earth, the conception of long and large tunnel in the electrical meaning is put forward. Taking a practical electrified railway tunnel as an example, impedances calculated from different formulas are compared and the relative errors of Carson＇s formulas are presented. The results demonstrate that the impedance error become larger with the increase of frequency and become smaller with the increase of earth resistivity, and has a value of above 5% even under the fundamental frequency. Physical interpretations are given to explain the results, and the suitability of Tylavsky formulas for conductors in long and large tunnel is discussed.