Effect of Mixed Layout of Parallel Cables on the Core and Sheath Current

Abstract

With the development of urbanization, overhead lines in urban areas are commonly transformed into the underground power cables. Since the single-circuit cables’ load, which is limited by the cross-sectional area of the cable, cannot be matched with the original overhead line, it has become one of the trends to use the parallel cables in phase. The sheath circulating current during normal cables’ operation can lead to the rise of temperature and influence the cable capacity and insulation life. In addition, the core current’s distribution for parallel cables is a key factor affecting the capacity. In order to investigate the effect of mixed arrangement and inconsistent length on the circulating current and current distribution of parallel cables, a model for calculating each circuit current of cross-connected grounding single-core cable is established, and the circulating current and core current under different arrangements or lengths of cross-connect section are calculated in this paper. The results show that the sheath circulating current can reach up to 30% of the core current when the mix of triangular and vertical arrangement are used for the cables; when the combinations of the length of cross-connected sections are 450 m-500 m-550 m and 450 m-525 m-525 m, both of sheath circulating current are less than 10% of the core current. It is demonstrated that parallel cables core current distribution mainly depends on the layout of each section of cable and after the layout is determined the length of each section has little effect. Thus, the mixed arrangement of parallel cables should be avoided as much as possible, and the length of each section can vary to some extent.