地下电力电缆集群的不等间距优化设计

Optimum Design of Underground Power Cables with Unequal Spacing

电缆载流量是电缆设计和运行中的一个重要参数。电缆集群等间距敷设时,互热效应使得敷设区域中央电缆的温度高于边缘电缆的温度。为提高地下电缆集群的输送能力,以电缆集群载流量最大为目标函数,以每根电缆温度低于其最高额定温度为约束条件,采用等值热路法和有限差分法分别求解了均匀土壤和不均匀土壤中电缆集群的载流量,并采用人工鱼群算法确定电缆的最优位置。计算结果表明,不等间距优化布置策略提高电缆群载流量的效率随回路数的增加和回填土热阻系数的增加而增加。不等间距优化设计提高了电缆群的载流量。

In densely populated areas, electricity is usually transported and distributed through buried cables in cluster laying. One of the most important needs in power cable engineering and operation is to have information about maximum current carrying capacity. The current carrying capacity is influenced by many factors such as the soil thermal resistivity and spacings between power cables. The temperature field of power cables is similar to the current field of grounding grids. In the design of substation grounding systems, variable spacing technique is often used to arrange grounding conductors. It can reduce the differences of disspating current density of grounding conductors as well as the maxmium touch voltage. Equal spacing is usually employed to arrange the power cables in cluster laying, Because of the mutual heating effect, the temperature of the central power cables is higher than that of marginal power cables. Variable spacing technique can also be utilized to reduce the differences of the thermal flow density of power cables. In order to improve the current carrying capacity of power cables, the IEC standard and the finite difference method are employed respectively to calculate the maximum ampacities of underground power cables in homogeneous soil or non-homogeneous soil. The maximum ampacity is taken as objective function. The constraint condition is that the temperature of any cable is lower than maximum permissible temperature. Artificial fish swarm algorithm is used to determine the optimum spacing. Because of the high capital costs of underground transmissiom systems, small differences in improving cable ratings can represent a considerable saving in investment. The calculating results show that unequal spacing can improve the ampaeity 5.8% and reduce the temperature differences of power cable conductors from 17℃ to 6℃ for 7 circuits in homogeneous soil. As the number of circuits or the thermal resistivity of backfill soil increases, the improved ampacities increase. Thus unequal spacing improves the am paeity of the power cables in cluster laying.