基于迭代法的单芯电缆载流量的研究

为解决电缆导体温度难测问题,采用迭代方法,以单芯电缆主绝缘能耐受的温升为依据,研究了单芯电缆的载流量。编程计算了单芯电缆金属护套两端直接接地及无环流时的载流量;讨论了环流对载流量的影响,并与IEC计算公式所得结果进行比较,验证了计算的正确性。并研究了双回路运行时,一回路电流对另一回路载流量的影响。结果表明,在两端接地方式下,金属护套环流对电缆载流量的影响很大,约为单端接地方式(无环流)的60%~80%。交叉互联接地方式下分段均匀的电缆,环流相对较小,对载流量的影响不大。负荷不均匀的双回路运行时,其中增加一回路负荷将使其临近回路的载流量减小。

Study of Ampacity of Single-core Cable Based on Iterative Method

The section of a cable and the control of its transmission capacity are influenced by the cable ampacity,which is determined by the long-term enduring temperature of its insulation.For difficulty in measuring the temperature of a cable conductor,the cable ampacity is usually calculated by the formula of IEC-60287,in which the conductor is supposed 90(if its insulation is XLPE) and the sheath reaches its maximal temperature.However,the maximal temperature of the sheath is related to the current flowed in cable conductor and its resistance.Therefore,strictly speaking,the IEC calculation formula is not so rigorous.In this paper,based on the heat-resistant ability of cable insulation,the ampacity of single-core cable with or without the so-called circulating current is calculated by modifying the cable conductor current till 90 .The influence of circulating current to cable ampacity is discussed,and IEC result is compared to prove the correctness of the calculation.In the meantime,we give the relationship curve of the ampacity of one circuit changing with another circuit current.From the calculation and analysis,the circulating current in sheath has a great influence on cable ampacity in two-terminal-grounding connection,in which the cable ampacity is 60%-80% of that in one-terminal-grounding connection(has no circulating current in sheath),and has less influence on cross-banding-grounding connection.The cable ampacity in one circuit decreases with the load increase of another adjacent circuit.