Analysis of line parameter symmetry and phase sequence arrange concerning four circuits on one tower

Asymmetry of line parameter has great impact on the safe operation of the power system and its relay protection´s performance, while different phase sequence arrange will affect the symmetry of transmission lines. A calculation method of sequence impedance parameter is firstly put for ward, concerning four circuits on one tower. On this basis, the paper analyzes the effect on line parameter symmetry of different phase sequence arrange by calculating single-sequence component unbalanced degree and composite-sequence component unbalanced degree. Further, superior phase sequence arrange schemes of same-voltage and mixed -voltage four circuits on one tower is proposed. The conclusion will contribute to the standard design of four circuits on one tower.