Explain the difference between the lumped and distributed parameters used in the modelling of transmission lines?

• Lumped parameters

1. In electrical circuits, the physical size of the element is negligibly small when compared with wave length of electromagnetic wave propagation.
2. The elements are thought of being concentrated at singular points in space. So the physical quantities depends only on Time.

• Distributed parameters

1. The physical size of the element is comparable with wavelength of electromagnetic wave propagation .
2. Distributed systems are built based on the assumption of being distributed in space. So the physical quantities depends both on time and space.

It is important to note that lumped and distributed are not properties of the system itself.

These are related to the size of the system compared to the wavelength of applied voltages and current.

For example an element is considered to be lumped if it's size is smaller than the wavelength of applied

voltage and current.

Short Transmission lines :- length = upto 60km , Voltage less than 20KV.

Medium Transmission lines :- length between 60 to 160km , Voltage between 20 to 100 KV.

Long Transmission lines :- length greater than 160km , voltage greater than 100KV.

The transmission line, with length less than 160 km, the parameters are assumed to be lumped and not distributed. Such lines are known as electrically short transmission line. This electrically short transmission lines are again categorized as short transmission line (length up to 60 km) and medium transmission line (length between 60 and 160 km).

The capacitive parameter of short transmission line is ignored whereas in case of medium length line the, capacitance is assumed to be lumped at the middle of the line or half of the capacitance may be considered to be lumped at each ends of the transmission line. Lines with length more than 160 km, the parameters are considered to be distributed over the line. This is called long transmission line.