Effect of parallel section and lines in parallel section on unbalance degree of UHV AC line is important.

Length and number of parallel section, active power of lines in common corridor have considerable influences on unbalance degree of double-circuit UHV AC line.

Proper length of parallel section should be chosen, and the number of parallel section and the one of the lines in every parallel section should be limited.

Ratio of rated active power of lines in common corridor should be at a lower level.