What is Travelling Waves

When a transmission line is connected to a voltage source, the whole of the line is not energized in one instant. This is because of presence of distributed constants (Inductance (L) and Capacitance(C)). When switch S is closed, the inductance L1 acts as open circuit and C1 acts as short circuit instantaneously. In this instant the next section (i.e, L2 and C2) cannot be charged as voltage across C1 is zero. So in order to charge the next section (i.e, L2 and C2) it will take finite time. The same argument applies to third and fourth sections and so on. Thus voltage build up in the sections will be in the form of a voltage wave traveling from source to load through the transmission lines and gradual charging of capacitance is due to associated current wave. Thus in a long transmission lines the voltage and current travels from source to load in the form of waves.