Calculation of the Three-Phase Current Unbalance of Multiple-circuit Cross-over Overhead Transmission Lines

Abstract

With the rapid development of power grid, more and more overhead transmission lines with the same tower, different voltage levels and different structures cross over, which makes the three-phase unbalance problem of transmission lines on the same tower more and more serious. Although there are many researches on the three-phase unbalance of the overhead transmission lines with the same tower, different voltage levels and different structures, there are few researches on the influence of the structure of crossover lines on the three-phase unbalance and how to design the line structure rationally. Therefore, this paper established the calculation three-dimensional model of the cross-over overhead transmission lines, considering the influence of a variety of circuit structure, proposed to the cross section structure of the wire, Matlab is used to calculate each paragraph and the other is not mutual impedance of parallel lines, finally respectively superposition of wires and wire, the mutual impedance between the cross-over lines impedance matrix, and the three phase current imbalance of the line. The analysis of the domestic cross-over lines shows that the method in this paper can accurately and quickly calculate the three phase current unbalanced degree of transmission lines in this special situation. What is more, this method also can analyze some significant factors which have great impact on the unbalanced degree such as the crossing angle, crossing distance and phase sequence arrangement. By this analysis, the best range of crossing angle and the optimal phase sequence can be obtained, which will provides professional reference for engineering design of cross-over transmission lines.