Let us consider the short circuit transient on a transmission line. Certain simplifying assumptions are made at this stage:

1. The line is fed from a constant voltage source.

 2. Short circuit takes place when the line is unloaded.

 3. Line capacitance is negligible and the line can be represented by a lumped RL series circuit.

                                    7.6  Transmission line model

With the above assumptions the line can be represented by the circuit model. The short circuit is assumed to take place at t = 0.

 The parameter α controls the instant on the voltage wave when short circuit occurs. It is known from circuit theory that the current after short circuit is composed of two parts, i.e.