# Classification of transmission lines

The general classification of transmission lines based on their length into short, medium and long is -
Short if length < 80 km
Medium if 80 km < length < 200 km
Long if length > 200 km
but this classification is for the case where frequency is 50 Hz. How is the classification done when frequency is not 50 for eg, classify the transmission line in short, medium or long if length = 100 km and frequency = 100 Hz.

• Please edit and ask a specific question - "Classification of transmission lines" is not a question. Commented Sep 26, 2023 at 9:03
• A long transmission line can be as short as 1 metre i.e. it completely depends on the frequency of excitation. Commented Sep 26, 2023 at 9:45

You do not cite where you found that classification.

However this can be answered in some generic way. A motivation to classify transmission lines for energy grids is to have rules of thumb which problems to expect. These are related to the electrodynamics of long lines.

Some questions/problems are:

• Will a branch of my network act as an antenna?
• Will we have to compensate for capacity of a line?
• Can a line elicit resonance when open, yielding twice the nominal voltage at some point?

Good thing is: You can apply a simple rule. There's reciprocity between frequency and length. So if you increase the frequency to e.g. 77 Hz, a short line in terms of that rule will be shorter than 60 km. This is correlated to the wavelength of that specific frequency.

However this logic shortcut shouldn't be stretched infinitely because at much higher frequencies there will be additional effects on local elements e.g. power poles and insulators.