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Transmission lines transposition and balance loading in all phases are the initial criteria for analyzing a power system with a symmetrical model. Untransposed transmission lines have different effects on the power system like voltage unbalance, reduced power-transmission capacity of the lines and increased losses in the lines. In this paper, the effects of unsymmetrical transmission lines on the performance quality of the power system will be studied. First, the effects of asymmetry of the power system on the balance of grid voltage will be discussed as an important power quality parameter. Then, its effects on decrease of power-transmission capacity of the lines will be analyzed. Line coupling and problems such as divergence of calculations would face the use of advanced existing software for analyzing unsymmetrical networks with some difficulties. In this paper, the amount of voltage unbalance in transmission and 132kV network of a case study power system located in Khorasan province in Iran will be calculated. After calculating unused capacity of transmission lines in this system, the financial consequences of this problem will be discussed at the end.