1. Short-Circuited Line – If the line is short-circuited at the receiving end, i.e., Z = 0, then the transmitted and reflected waves arc given as:

The unique characteristic of the short-circuit is that voltage across it is zero. When an incident voltage wave E arrives on short-circuit, the reflected voltage wave must be -E to satisfy the condition that the voltage across the short-circuit is zero. The waves are shown in fig. 4.

2. Open-Circuited Line – If the line is open- circuited at the receiving end, i.e., Z is infinite, the transmitted and reflected waves are given as:

An open-circuit at the end of a Line demands that the current at that point is always zero. Thus when an incident current wave I arrives at the open-circuit, a reflected wave equal to – I is at once initiated to satisfy the boundary condition. The waves are shown in fig 5.

3. Line Terminated By an Impedance Equal To Surge Impedance – If the line is terminated with an impedance equal to surge impedance, i.e., Z = Zc, we have

4. Line Connected To a Cable – A wave travelling over the line and entering the cable, as shown in fig 6, looks into different impedance and, therefore, it suffers reflection and refraction at the junction

The refracted or transmitted voltage is given as:

The other waves can be had by employing the relations (8), (9) and (10). The surge impedances of the overhead line and cable are approximately 500 Ω and 50 Ω respectively. With these values it can be seen that the voltage entering the cable will be

or roughly 20% of the incident voltage.

This is the reason that an overhead line is terminated near a station by connecting the station equipment to the overhead line through a short length of underground cable. Besides the reduction in magnitude of the voltage wave, it also reduces the steepness of the wave. It is because of capacitance of the cable. The reduction in steepness is very important because it is one of the factors for reducing the voltage distribution along the equipment windings. In connecting the overhead line to a station equipment through a cable the important point to be remembered is that the length of the cable should not be shorter than the expected length of the wave otherwise successive reflections at the junction may cause piling up of voltage and the voltage at the junction may attain the value of incident voltage.

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