Transposition in

Transmission Lines

K-13EL-79

Presentation

ON

Zulfiqar Mangrio

Introduction

When 3-phase line conductors are notequi-distance, then flux linkages andinductance of each conductor are notsame.

A different in inductance in eachphase results in unequal voltagedrops.

In order that voltage drops equal in allconductors, we generally interchangethe position of conductors at regularinterval; called transposition.

Transposition

Transposition of Conductors refers to

the exchanging of position of

conductors of a three phase system

along the transmission distance

in such a manner that each

conductors occupies the original

position of every other conductor over

an equal distance.

Electrical Transmission lines

In Single circuit AC transmission line 3

conductors of all the 3 phases are

unsymmetrical placed.

Due to unsymmetrical spacing of the

conductors Inductance and Capacitance of

each conductors becomes different.

Suppose we assume that resistance is

same for all the three conductors than

due to difference in inductance and

capacitance, all the three conductors

will have difference in Impedance.

So, due to difference in impedance

Voltage drop is different and

unbalance of voltage is obtained.

Use of Transposition

Transposition of electrical

transmission line is must, when Long

AC transmission line is to be erected.

Because Voltage unbalance in Long

transmission line becomes remarkable

and cannot be tolerated.

In case of short transmission line it

does not create much imbalance in

voltage.

So, to make this voltage unbalance

to minimum, the conductors are

transposed such that the relative

position of three phase conductors is

interchanged after certain length of

transmission line by putting Special

Transposition towers.