Electronic – happening, physically during a Transmission Line Reflection in a closed and open circuit scenario

power electronicstransmission line

I am having trouble understanding what is happening physically during a transmission line reflection, in particular the short circuit and open circuit case. I understand that when when a transmission line is terminated with a resistance equal to the transmission line impedance, then

$$ \Gamma = \frac{R_T – Z_o}{R_T + Z_o} = 0 $$

which means that there is no reflection, and physically it makes sense because the resistor is dissipating power through it, and so therefore the wave cannot propagate back. However, I don't understand what is happening in the closed and open circuit cases.

In this post On a transmission line why are voltage and current waves reflected at a short circuit? the answer makes sense in a power perspective for the short circuit case, but I don't understand why the reflected wave is inverted. This post Transmission Line reflection. I would like a non-mathematical explanation seems to answer the question with

But now we have another unstable situation: That end of the line is at 0V, but the rest of the line is still charged to Vs/2. Therefore, additional current flows into the short, and this current is equal to VS/2 divided by Z0 (which happens to be equal to the original current flowing into the line). A voltage wave (stepping from VS/2 down to 0V) propogates in the reverse direction, and the current behind this wave is double the original current ahead of it.

but I don't understand why additional current flows into the short. Is this some application of Len's Law? Or is there something that I am missing? Also, what happens when the reflected wave reaches the voltage source? There would be an enforcement of some voltage so would it be inverted again?

For the open circuit case, I understand that voltage "Piles up" at the end of the transmission line since there is no path for it to continue traveling, but why is it twice as much voltage as what is started with? Mathematically, it makes sense, but I still don't understand this physically.

Any help would be great, I am very confused about this topic and would like to get a firm physical understanding before accepting the equations. Thank you!

edit:
I walked through the equations a few hundred times, and was able to figure out what is happening physically.

Best Answer

This video explains it so well for being so old. Bell Labs experiment of wave propagation