翻译以下段落为英语：其次针对牵引回流分布分析的问题根据实际情况下带回流线的直接供电和AT供电系统中电流的路径及走向通过对直供方式下的电路模型求解得到钢轨电流和电位的分布情况推导出直供系统牵引变电所接地网回流的求解公式。由于AT供电方式下牵引网结构复杂提出采用恒定电流场原理推导出钢轨泄漏电流以及综合地线泄漏电流在大地中产生的电位公式从而推导出AT供电系统中牵引变电所接地网回流的求解公式；在此基础上运

Secondly, to address the problem of traction return distribution analysis, based on the actual current path and direction of the direct supply and AT supply systems with the return line, the distribution of rail current and potential under the direct supply mode is obtained by solving the circuit model, and the formula for calculating the grounding network return flow of the traction substation in the direct supply system is derived. Due to the complex structure of the traction network under the AT supply mode, the principle of constant current field is proposed to derive the formula for rail leakage current and the potential generated in the ground by the comprehensive ground leakage current, and thus the formula for calculating the grounding network return flow of the traction substation in the AT supply system is derived. Based on this, two simulation models of traction return flow are established using CDEGS grounding analysis software, based on the Handan-Changzhi Line and the Shitai Passenger Dedicated Line respectively, for the two supply modes. The reliability of the simulation model is verified by comparing the grounding return flow calculated theoretically with the simulation results. Based on the simulation model, the influence of factors such as the distance between locomotives and traction substations, soil resistivity, and the number of distribution conductors in the grounding network of the substations on the distribution status of traction return flow under different supply modes is analyzed in detail.