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.