Definition: The transposition is a physical rotation of the conductors so that the conductor is moved to take up the next physical position in the regular sequence. The transposition of the conductor equalises the mutual inductance and capacitance between the lines. The irregular spacing between the conductor gives a complex value of inductances which makes the study of the power system complex. The transposition is mainly done in the switching station and the substations. The transposition cycle is shown in the figure below.
Needs of Transposition
The inductance of unsymmetrical line causes voltage drops even if the voltage is in a balanced condition. Because of the inducing voltages, the magnetic field exists in the conductor which causes the interference in the line. This can be reduced by continually exchanging the position of the conductor, which can be done by transposition the conductors.
The transposition of the lines can be done by placing the one-third segment of all three phases of the conductor in the same line. The transposition balance the capacitance of the line due to which the voltage is also balanced.
Disadvantage of Transposition
Frequently changing the position of conductors weakens the supportive structure which increases the cost of the system.