My questions are:
* Why do we assume the bottom wire(ground) has a constant voltage while the upper isn't?
* Shouldn't the model be symmetric. why getting voltage drop across the upper wire while zero across the lower one?
* Why not add inductor and resistance throw the bottom wire aswell?
* Is there any derivation from Maxwell's equations to get Telegrapher's equation(like KVL and KCL)?
I know that the model has experimental facts and so on. My aim is to understand how to come up with this model in a rigorous way.
Hello Islam,
The upper wire represents the physical conductor that transfer the power from the sending end to the receiving end. Therefore, its series and shunt equivalent impedances are represented in the per phase equivalent circuit.
On the other hand, the bottom wire represents the equi-potential nature of the earth which is provided by the earthing system. Therefore, all the points comprisin this wire have the same voltage. The ideal value of this voltage is zero considering a perfect grounding.
Regarding the mentioned proofs, the Stevenson's relevant textbook is a good choice.
Thanks Dr.Mohamed for your time,
But the bottom wire isn't grounded in general. I mean in small communication system(demo) such as two long(electrical length) wires with an oscillator L=275 cm f=88mhz.
I have check your mentioned book chapter 6, but he starts with almost the same model with similiar discussion like my microwave book.
OK Islam. Your question is now clearer. Generally, a model is an equivalent representation of a real system or item. The models are constructed for specific purposes. Their validity is limited under these conditions of applications, and the imposed simplifications. In the mentioned TL, the overall impedance of the wire loop are lumped in the upper wire. This equivalence is valid for power loss, and voltage drop as well as other quasi-static analysis. Search the Google scholar for an old reference that constructs this model. I will try to find a good reference for you. Anyway, it is interesting to see you asking these queries. Good luck
This 1957 book is good in current fundamentals, but it is oriented to the electical power engineering.
The equivalent model is valid for power circuits for a small length . A three phase cascade model with couplings is more accurate. These models used for surge propagation studies do differentiate phase mode propagation from ground mode propagations. Yes ground does play a role and can be represented in more detail, but usually the studies need a reference voltage with zero voltage to build up the Matrices and it is found convenient to have ground as reference in AC studies. More detail representation is required in HVDC system electrode line design etc.
- Badges
- Science topic
- Similar topics
- Engineering
- Modeling