Question

Q2:

a) The resistance of a transmission line is effected by some factors. Explain these factors.

b) Show that the inductance of a conductor due to internal flux is given by: L=(1*10^-6)/2 H/m

c) Derive in expression for the inductance per phase for a 3- phase overhead transmission line when conductors are of equilateral spacing.

d) What is the effect of unsymmetrical spacing of conductors in a 3-phase transmission line.

Answer 1

a)Resistance of a cunductor depends upon its:

● Length :

Length of the cunductor is directly proportional to the resistance offered by the cunductor.

i.e. R∝l

● Area of cross section :

Area of cross section of the cunductor is inversly proportional to the resistance of the cunductor.

i.e. R ∝ 1/A

●Nature of its material:

Resistance offered by cunductors vary as per the nature of the material of conductor vary.

●Temperature.

When temperature increase , Resistance also increase

b)

c)

d)

If the space between the conductors of the 3 phase system is not equidistant(unsymmetrical spacing), the flux linkage and inductance of each phase would differ from one another. Because of the different inductance in each phase,the voltage drop will be different in each phase even though the currents in the conductors are balanced. Therefore, the receiving end voltages is not same in all the phases. This is major effect of unsymmetrical spacing of 3 phase transmission line.in order to reduce it transposition is done.