AliMohammad Mohammadi - Monenco Iran Consulting Engineers Tehran, Iran
Masoud Abdolhosseinpour - Monenco Iran Consulting Engineers Tehran, Iran
Siamak Hossein Khalaj - Monenco Iran Consulting Engineers Tehran, Iran

One of the most important challenges in design of power transmission lines is need for line transposition that depends on length of lines, average transfer power, voltage level and phases configuration. This paper describe calculation of additional ohmic losses of a non-transposed line and then develops a method to determine minimum length of transmission lines, as a proper criterion for need of transposition, considering transmission lines design and operation limitation according to economic comparison between prime costs of installation (prime cost of investment) and benefits due to reduction of additional ohmic losses, considering desirable time to return to mentioned cost

Transposition; Power Transmission Lines; Ohmic power Losses; Unbalance Currents