双回路电缆护套环流计算及影响因素分析

Calculation of Circulating Current in Sheaths of Two-circuit Arranged Cables and Analyses of Influencing Factors

为分析电缆线路中的环流,推导了双回路敷设电缆护套环流的计算方程,并自行编制运算程序实现了计算机求解。结合某电力设计院两回路电缆的实际敷设及运行参数,计算了直线排列交叉互联情况下电缆护套中的环流,并对影响金属护套中环流值大小的相关因素作了简单分析,减小环流值的方法有增大接地电阻、使电缆紧密排列、保证电缆交叉互联段长度相等等。同时,提供了对应单回路敷设情况下的计算结果进行比较,结果表明计算护套环流时双回路不能以单回路情况简化。相关推导过程及程序设计思想可推广应用于双回路电缆的其它敷设形式或更高回路数的电缆线路。

For single-core cables widely used in high or super-high power systems, induction voltage will cause circulating current flowing in the loop of the cable sheaths and the earth or the reflux wires. This current will produce additional losses, so as to reduce the current capacity of the cables, and the grounding wire will be burnt out when the heating effect is serious. Analyses on the circulating current in cable systems have been reported in some documents, but they are only for single circuit networks. In recent years however, two- and three-circuit cable networks are increasingly applied in cities, so accordingly the determination of the circulating current in these arrangements causes much attention. Thus the research work is focused on the calculation method for circulating current of a two-circuit cable network in linear arrangement. What presented first is the equivalent circuit for the circulating current calculation. Then the equations to calculate the circulating current in metal sheaths of two-circuit arranged cables are deduced and the basic principles of the solution program for this specific issue are provided. After parameter values are assigned according to the lay and operation condition of cables in two-circuit arrangement of a power designing institute, the circulating current in cross-bonded cable sheaths in linear arrangement are calculated. According to the calculation results, the analyses on influencing factors are carried out, and some possible ways to reduce the circulating currents are presented, such as to increase the earth resistance, to lay cables closely, and to make the cable length of every cross-interconnect segment equal. Besides, results from the single-circuit linear arrangement are also provided, for the comparison to be made with the two-circuit one. It is shown that two-circuit arrangement cannot be simplified as single-circuit when calculating circulating currents in cable sheaths. Although the calculation equations and the solution program in this paper are specially for the two-circuit linear-arranged cable networks, the technique for equation deduction and program design can be extended to cables in other lay conditions of two-circuit arrangement or even more circuit number.