电气化铁路27.5kV单相单芯交联聚乙烯电缆载流量计算

Ampacity Calculation of 27.5kV Single-phase Single-core Cross Linked Polyethylene Power Cables in Electrified Railways

电气化铁路单相供电电缆是电气化铁路运行的关键组成部分,为获得铁路专用27.5kV单相单芯交联聚乙烯电缆的载流量,通过仿真计算的方法进行了研究。首先对电缆的运行情况进行分析,用有限元法对比计算了单相供电与三相供电条件下电缆金属护套涡流与环流损耗。在对电缆的环流损耗与涡流损耗计算的过程中,通过对计算单元自由度的修改与温度场的耦合,为电气化铁路单相供电电缆载流量计算建立更为精确的计算模型。在该模型的基础上,根据铁路电缆实际敷设环境,分析了不同接地方式、线芯间距、回路数量、媒质热阻、环境温度下电缆载流量的变化。结果表明:双端接地方式下铁路单相供电电缆金属护套层环流损耗较三相供电提高约75%,单端接地方式下相位影响不明显;电缆温升受相邻电缆间距、周围媒质热阻及温度影响较大;回路数增多,受临近电缆的影响,中间电缆的温升将导致电缆整体载流量下降。

We numerically researched the ampacity of 27.5kV single-phase single-core power cables that were used in traction substation.The operating condition was analyzed based on calculations of the circulation loss and eddy current loss of the cable under single-phase and three-phase conditions respectively by using the finite element modeling（FEM）method.A more accurate ampacity calculating model of the cable for cases with single-phase power supply was established by modifying the degree of freedom of the calculating unit and by coupling the thermal analysis of calculation the temperature distribution.On the basis of the model,according to the actual environment of railway cable,changes in the cable ampacity were analyzed in different grounding connections,cable distances,loop numbers,thermal resistances of surrounding media and environment temperatures.Several conclusions can be drawn as follows：for a cable with sheath layers grounded in two terminals,its circulation loss in single-phase mode is 75% more than that in three-phase mode,while the phase condition has little effect on cables with sheath layers grounded in one terminal;the distances between cables,the thermal resistance of surrounding media,and the environment temperature affect the cable temperature seriously;with the increase of cable loops,the temperature of the cables in the middle of the cable loops rises obviously which will result in an overall ampacity decrease of the cable group.