电缆额定电流计算中最重要的任务是确定给定电流负载下的导体温度，或者相反，确定给定导体温度下的容许负载电流。为了执行这些任务，必须计算给定导体材料和给定负载下，电缆内产生的热量及其远离导体的耗散率。周围介质的散热能力在这些测定中起着非常重要的作用，并且由于土壤成分、含水量、环境温度和风条件等因素的影响而变化很大。 热量通过电缆及其周围环境以多种方式传递。对于地下装置，热量通过导体、绝缘、屏蔽和其他金属部件的传导进行传递。可以根据附录A（方程式A.1）中所示的适当传热方程式对传热过程进行量化。 电力电缆的额定电流计算需要热传导方程的解，该方程定义了导体电流与电缆及其周围环境中的温度之间的函数关系。 解析求解这些方程的挑战通常源于难以计算电缆周围土壤中的温度分布。当电缆被表示为放置在无限均匀周围介质中的线源时，可以得到解析解。由于这不是电缆安装的实际假设，因此通常使用另一种假设；也就是说，地球表面是等温线。在实际情况下，电缆的埋深约为其外径的十倍，对于此类电缆达到的通常温度范围，等温地球表面的假设是合理的。 在这种假设不成立的情况下；也就是说，对于大直径电缆和位于地面附近的电缆，必须对解决方案进行修正，或者应采用数值方法。 假设电缆位于均匀半无限介质中，利用等温表面边界，可以求解稳态热传导方程。 对于大多数实际应用，IEC 60287（稳态条件）和IEC 60853（循环条件）中描述了热传导方程的求解方法。当这些方法无法应用时，可以使用数值方法求解热传导方程。 其中一种方法特别适用于地下电缆的分析，即本文介绍的有限元法。

The most important tasks in cable current rating calculations are the determination of the conductor temperature for a given current loading or, conversely, the determination of the tolerable load current for a given conductor temperature. In order to perform these tasks the heat generated within the cable and the rate of its dissipation away from the conductor, for a given conductor material and given load, must be calculated. The ability of the surrounding medium to dissipate heat plays a very important role in these determinations and varies widely because of factors such as soil composition, moisture content, ambient temperature and wind conditions. The heat is transferred through the cable and its surroundings in several ways. For underground installations the heat is transferred by conduction from the conductor, insulation, screens and other metallic parts. It is possible to quantify the heat transfer processes in terms of the appropriate heat transfer equation as shown in Annex A (equation A.1). Current rating calculations for power cables require a solution of the heat transfer equations which define a functional relationship between the conductor current and the temperature within the cable and its surroundings. The challenge in solving these equations analytically often stems from the difficulty of computing the temperature distribution in the soil surrounding the cable. An analytical solution can be obtained when a cable is represented as a line source placed in an infinite homogenous surrounding medium. Since this is not a practical assumption for cable installations, another assumption is often used; namely, that the earth surface is an isotherm. In practical cases, the depth of burial of the cables is in the order of ten times their external diameter, and for the usual temperature range reached by such cables, the assumption of an isothermal earth surface is a reasonable one. In cases where this hypothesis does not hold; namely, for large cable diameters and cables located close to the ground surface, a correction to the solution has to be used or numerical methods should be applied. With the isothermal surface boundary, the steady-state heat conduction equations can be solved assuming that the cable is located in a uniform semi-infinite medium. Methods of solving the heat conduction equations are described in IEC 60287 (steady-state conditions) and IEC 60853 (cyclic conditions), for most practical applications. When these methods cannot be applied, the heat conduction equations can be solved using numerical approaches. One such approach, particularly suitable for the analysis of underground cables, is the finite element method presented in this document.