Basis of Classification of Transmission Line

Date: 2017-03-14   Clicked: 349

Basis of Classification of Transmission Line

The length of the Transmission Line at its voltage level decides its classification as Short / Medium /Long Transmission Lines. A typical transmission line circuit looks like as shown below.

We can see that there are infinite numbers of cascaded units in a Transmission Line. If we want to analysis, it is a very hectic job taking care of so many cascaded units. Therefore we engineers come up with some approximations.

The accepted conventional distances are,

  • Short Transmission Line: 0 to 80 Km
  • Medium Transmission Line: 80 to 160 Km
  • Long Transmission Line: 160 Km and above
When a line is classified as one the three mentioned above, it is a guideline for power engineers to compute their parameters i.e. R, L and C.

Short Transmission Line:

For a distance like 80 km if we don’t consider the shunt capacitance and conductance the calculation. So the below picture is a model of a short transmission line, where we take the entire element as Lumped element.

Medium Transmission Line:

For a distance in between 80 km to 160 km we consider capacitance only at the sides for a pi model.

Long Transmission Line:

For a distance more than 160 km we have to consider all the distributed elements and then calculate the parameters. In this case we cannot consider lumped parameters rather we need to consider distributed parameter and make necessary integration for the sake of calculation.

The Electrical Power is transmitted over a Transmission Line with a speed of light that is 3×108m/sec. Frequency of the power is 50 Hz. The wave length of the voltage and current of the power can be determined by the equation given below,

                                                                    f.λ = v

where f is power frequency, λ is wave length and v is the speed of light.


Hence, the wave length of the transmitting power is quite long compared to the generally used line length of Transmission Line.


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