The IEC Standard 60287-1-1 contains the formulae for the calculation of the sheath and armor loss factors of a 3-phase cable system. Sheath circulating current losses are computed for single-, multiple-, or cross-bonded systems. This paper deals with cross-bonded cable systems. For unequal minor section lengths, the standard gives a formula allowing calculation of the circulating current losses when the lengths of the minor sections are known. The origin of this formula is not documented; hence, this paper gives its derivation. When the lengths of the minor sections are not known, the standard suggests using a factor of 0.004, which multiplies the circulating current loss factor computed for a multi-point bonded system. In this paper, the cable sheath circulating loss factor was found using different methods with the aim of checking the applicability of the 0.004 multiplier to practical cable systems with differences in the length of minor sections and system voltage. Three different cable systems are studied; the first is a 132 kV circuit with known lengths of minor and major sections. The second circuit is a 220 kV system where the lengths of minor sections are unknown and the third is a 220 kV real system with known, highly irregular section lengths. The calculated values of sheath circulating current loss factor, applying the formulas from the IEC 60287-1-1, were compared to the values calculated based on practical measurements of sheath induced voltages and currents. The effect of taking the measured and IEC values on the continuous current rating (ampacity) is also presented for the first two circuits and the comparison of the unknown and known section lengths for the third circuit is offered.

中文翻译：

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具有未知小截面长度的交叉粘合电缆系统的护套损耗因子 IEC 标准的现场验证

IEC 标准 60287-1-1 包含计算三相电缆系统的护套和铠装损耗因子的公式。护套循环电流损失是针对单、多或交叉粘合系统计算的。本文涉及交叉粘合电缆系统。对于不等的小节长度，该标准给出了一个公式，允许在已知小节长度的情况下计算循环电流损失。这个公式的起源没有记录；因此，本文给出了它的推导。当次要部分的长度未知时，标准建议使用 0.004 的系数，该系数乘以为多点粘合系统计算的循环电流损耗系数。在本文中，电缆护套循环损耗因子是使用不同的方法找到的，目的是检查 0.004 乘数对实际电缆系统的适用性，这些电缆系统在次要部分的长度和系统电压方面存在差异。研究了三种不同的电缆系统；第一个是 132 kV 电路，具有已知长度的次要和主要部分。第二个电路是一个 220 kV 系统，其中次要部分的长度未知，第三个是一个 220 kV 实际系统，具有已知的、高度不规则的部分长度。应用 IEC 60287-1-1 中的公式计算出的护套循环电流损耗因子值与基于护套感应电压和电流的实际测量值计算得出的值进行了比较。