高压电力电缆金属护套下的热阻特性分析

IEC60287标准是电力电缆线路温度监测及载流量计算的理论基础与依据,为实现对IEC60287标准在线路载流量计算与电缆线路温度监测上的准确运用,通过对某国产电缆的载流量温升试验,研究了单芯高压电力电缆各层的温度分布并根据温度分布按照IEC60287的热传导模型推算出了单芯高压电力电缆各层的热阻值。利用IEC60287标准计算的单芯高压电力电缆的热阻参数与实际推算值比较表明,电缆导体与金属铝套间热阻的理论值与试验值之间存在有56.8%的差异。研究结果发现,阻水带及金属护套与电缆线芯之间存在的气隙是产生这种差异的主要原因。针对电力电缆的实际结构,在IEC60287标准基础上提出了一种改进的计算方法,该方法将电缆导体与铝套间部分分为热阻值不同的2层进行计算,并根据实际温升试验得到的热阻值提出了电缆导体与金属护套间的组合热阻系数的修正值为20.0Km/W,高于标准规定的6.0Km/W。

Thermal Resistance Properties of the Part between Metal Sheath and Conductor in High-voltage Power Cable

To appropriately apply the IEC 60287 standard to both the on-line temperature monitoring and current rating calculations in power cable lines,the current rating experiments were performed on one single-conductor high voltage power cable,from which not only the temperature distribution but also the thermal resistance of each layer were obtained according to the thermal conduction model provided by IEC 60287. Then,the experimental values of thermal resistance were compared to the theoretical ones obtained directly from IEC 60287 standard. The results show that the experimental value of thermal resistance of the part between metal sheath and conductor is much different from the theoretical prediction by 56.8%,which is attributed to the gas gaps among waterstop,metal sheath and conductor. Therefore,according to the specific structure of power cable,an improved method to calculate the thermal resistance between metal sheath and conductor in the cable was proposed on the basis of IEC 60287,in which the part between metal sheath and conductor is treated as two layers with different thermal resistance. In addition,according to the experimental values of thermal resistance,the modified thermal resistance coefficient of the part between metal sheath and conductor is estimated as 20.0 Km/W,which is far more than the standard value of 6.0 Km/W.