Representation of Transmission Line

Representation of Transmission Line

In case of short transmission lines, the capacitive effects are small and neglected with some loss in the accuracy. It is required to consider only the resistance and inductance of the line. Fig. 2.3.1 shows a star connected generator supplying a balanced Y connected load through a short transmission line.

Whether the parameters R and L are lumped or distributed it makes no difference so far as measurements at the ends of the line are connected. The generator is represented by an impedance connected in series with the generated e.m.f. of each phase.

In case of medium length transmission line, R and L are taken as lumped as shown in the Fig. 2.3.2. with half the capacitance to neutral of the line lumped at each end of the equivalent circuit. The shunt conductance G is neglected as the current is same throughout the line while calculating voltage and current.

In case of long transmission lines the parameters associated with the line are taken as distributed one to obtain high degree of accuracy in the analysis.

The transmission lines are usually operated with balanced three phase loads. The lines may not be spaced equilaterally and not transposed. The unsymmetry obtained is less and phases are said to be balanced.