• Short Transmission Line
• Medium Transmission Line
• Long Transmission Line

Short Transmission Line

• A transmission line having its length under 80 kilometer is taken into account as a short transmission line. In short transmission line capacitance is neglected due to little leak current and alternative parameters (resistance and inductance) ar lumped within the transmission line.

• Medium length transmission lines are “the transmission lines whose length is between 80 kilometer and 250 km”. The voltage transmission ability of those medium length transmission lines is around 20 kilovolt to 100 kilovolt.
• For a medium transmission line, charging current is substantial and due to the length of the line the shunt admittance plays a significant role in the calculation of the effective parameters of the line.
• The shunt admittance and series impedance are considered as a lumped parameter of the medium transmission line. The medium transmission line is shown below in the diagram.

• Many localized capacitance models have been used to make approximate line performance calculations. The following models are commonly used.
  • Nominal T model
  • Nominal ∏ (pi) model

• A power transmission line with its effective length of around 250 Kms or higher than is stated as an extended transmission line. The line constants area unit uniformly distributed over the whole length of line.