Effects of unfavorably transposed transmission lines

The correct transposition of overhead lines is crucial for optimal operation. Often, the conductor sequence is determined in a late planning step. In this case, there is a risk that the transposition is not designed in an optimal way. Unfavorably transposed lines lead, for example, to unbalanced currents and voltages at the points of common coupling and therefore to increased field strengths in the direct area of the line. This paper shows how the transposition should be designed in order to ensure symmetry of the line. It also includes a discussion of the formation of the coupling matrices and an advanced, detailed representation of the unbalance, which allows for a more comprehensive analysis of the system behavior. The effects of unfavorably transposed overhead lines are presented taking into account the electrical unbalance. Conventional transposition variants are compared and it is shown that a one-third separation of the line length does not automatically lead to a symmetrical line. The unbalance is calculated as a function of the conductor sequence at the beginning of the line, depending on the load, and is compared and evaluated for correctly and unfavorably designed transposition. As a result, it is shown that transposition variations exist which can produce symmetrical operating lines independently of load situation.