What are the criteria for the classification of transmission lines as short, medium and long lines?

Classification of transmission lines (Power):

The network of transmission lines is formed by three phase AC system. This is required for Bulk power transfer from large group of generating stations to main transmission network.

Short power transmission line: 

Short distance power transmission lines has voltage ≤  11000 volts. These lines are required to carry power from main sub-station to local distribution area. Further power supply is distributed through pole mounted sub- station or plinth mounted sub-station.

Medium power transmission line: 

Medium distance power transmission line has voltage range 33-132 kV. For the economic voltages for medium lines an approximate rule is 1 kV/mile or 0.6 kV/km. kV= 5.5 √km x 0.6 + kW/100. These lines supply power directly to big organization or industry, which establishes own sub-station. 

Long power transmission line:

A long distance power transmission line has voltage range 220 kV to 750 kV. These lines are used for transfer of power from sending end to receiving end or for system interconnection for exchange of power between independently controlled networks. For longer transmission lines, higher power transmission voltages are necessary (p α v^2). Higher voltage gives lesser current, lesser I^2R losses, higher power transferability.

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