电缆.额定电流的计算.第2-1部分:热阻.热阻计算

[中文适用范围]： “IEC 60287 的这一部分仅适用于电缆在所有交流电压@和高达 5 kV 的直流电压@直接埋在地下@管道@槽内或钢管@两者的稳态运行条件且土壤和电缆在空气中不会部分干燥。术语“稳态”是指连续恒定电流（100% 负载系数），刚好足以渐近地产生最大导体温度@假定周围环境条件恒定。IEC 60287 的这一部分提供了热阻公式。给出的公式本质上是字面意思，并且有意保留某些重要参数的选择。这些参数可分为三组： 与结构相关的 C 参数根据已发表的作品选择代表值的电缆（例如@绝缘材料的热阻率）；与周围条件相关的C参数，这些参数可能变化很大@其选择取决于电缆所在的国家/地区使用或将要使用； ?C 参数，由制造商和用户之间的协议产生，涉及服务安全裕度（例如 @ 最大导体温度）。 IEC 60287 本部分中给出的用于计算直接埋在地下或埋地管道中的电缆的外部热阻的方程适用于有限数量的安装条件。当分析方法无法用于计算外部热阻时，可以使用有限元方法。 IEC TR 62095 中给出了使用有限元方法计算电缆额定电流的指南。 [外文原描述]： IEC 60287-2-1:2015 is solely applicable to the conditions of steady-state operation of cables at all alternating voltages, and direct voltages up to 5 kV, buried directly in the ground, in ducts, in troughs or in steel pipes, both with and without partial drying-out of the soil, as well as cables in air. The term "steady state" is intended to mean a continuous constant current (100 % load factor) just sufficient to produce asymptotically the maximum conductor temperature, the surrounding ambient conditions being assumed constant. This part of IEC 60287 provides formulae for thermal resistance. This second edition of IEC 60287-2-1 cancels and replaces the first edition, published in 1994, Amendment 1:2001, Amendment 2:2006 and Corrigendum 1:2008. This edition includes the following significant technical changes with respect to the previous edition: a) inclusion of a reference to the use of finite element methods where analytical methods are not available for the calculation of external thermal resistance; b) explanation about SL and SA type cables; c) calculation method for T3 for unarmoured three-core cables with extruded insulation and individual copper tape screens on each core; d) change of condition for X in 5.4; e) inclusion of constants or installation conditions for water filled ducts in Table 4.