重载流多芯电缆周围的磁场I.理论模型

Magnetic Fields around Heavy-Current-Carrying Multi-Core Cables I. Theoretical Model

多芯电力电缆在低压配电系统中常被用作配电干线 .这种重载流电缆周围的极低频磁场可能干扰附近敏感电子设备的正常运行 ,甚至影响暴露于该场下的人体的健康 .为分析这种磁场的分布特性 ,建立了多芯电缆周围磁场的载流平行螺旋线模型 ,并推导了周围磁场的简化计算公式 .基于所提出的理论模型对电缆周围磁场的特性进行了分析 ,发现在电缆的半径方向上磁场随距离衰减的速度大于指数衰减速度 .在平行于电缆轴线的直线上和在电缆的同轴圆周线上 ,磁场的幅值和相角都随观测点的位置周期变化 .理论计算结果表明 ,常用规格的多芯电力电缆在载额定电流的情况下 ,距电缆 2 m外空间中的磁场已小于有关国际标准的限值 .

For understanding and evaluation of such ELF magnetic fields, current-carrying parallel-helix-filament theoretical model was proposed. Based on the model, theoretical and simplified formulas for calculating the magnetic fields were deduced. The patterns of the magnetic fields are disclosed. It is found that the magnetic field decay with the radial distance at rate greater than exponentially. On an observation path parallel to the cable axis, or on a coaxial circular path, both the magnitude and the phase angle of the magnetic field change with the observation position periodically. The magnetic fields around some cables predicted by the proposed simplified formulas were compared with the limits in some international standards. It is found that for most of the cables employed in engineering practices, in the space of 2 meters away from the cable, the magnetic fields are in compliance with the standards.