Electronics > Beginners
Isolation transformer and electrons
ArthurDent:
IanB – I don’t see where anything I have posted has been incorrect in my posts describing the proper use of grounding, getting shocked, or correct wiring principles. Please look at the last diagram I posted. The diagram of the Isolation transformer I show and showed previously in post #20 is exactly what Hero999 later showed to demonstrate whether you get shocked or not on primary or secondary of an isolation transformer-there is no disagreement there at all. I clearly show that touching ground and a hot wire referenced to ground is dangerous but that has nothing to do with the correct circuit return being a wire as universally used.
It is the continual claiming that ground is used as the return current path for an electrical circuit, not just for safety, that I see as absolutely wrong. Hero999 even linked to rarely used single wire feed with earth return so using earth for the return circuit instead of a wire is what they meant and are presenting, not a grounded person accidentally touching a live wire and getting shocked. I have presented links to technical references to show that using a return wire and not relying on ground is universally accepted and I don’t see any disagreement with the references. I also don’t see what I have posted as condescending, instead saying that I’m silly and wrong without being able to explain how anything I have said is incorrect is what I see as somewhat condescending.
So simply put it is this. I have continually said and shown that a person can get shocked by touching a live wire that is referenced to ground. Probably all of us have gotten shocked at one time or another. I have also said that in an proper electrical circuit there is a neutral wire that is also bonded to ground (why else would you use an isolation transformer?) and it is the wire, not the somewhat resistive ground, that is the circuit return path back to the source. How is that in any way incorrect?
IanB:
Nothing you have said is incorrect, but neither have a seen a "continual claiming that ground is used as the return path for an electrical circuit", so there seems no need to correct that. There has been perhaps a misleading drawing, and a reference to the rare use of single wire earth return, but this is not the same as "continual claiming". On the whole everyone just seems to be violently agreeing with each other.
Anyway, I'll let it rest.
cdev:
Some power systems in Australia, New Zealand and elsewhere use ground for returns. Because of the lower cost. But not many.
https://en.wikipedia.org/wiki/Single-wire_earth_return
There is a history of power systems in Australia on the IEEE site that goes into a lot of detail about the systems' evolution there.
Zero999:
--- Quote from: ArthurDent on December 12, 2018, 08:54:24 pm ---Post #40 Hero999 – “In the distribution transformer scenario, the earth simply acts as a return conductor for the current path.”
Post #46 Hero999 – “I did read your posts, but they refer to distribution transformer, rather than the original poster's set-up.
As in your post #40 I am indeed talking about the distribution transformer scenario, as you were.
Hero999 – “The original poster is also in Europe and you refer to a US distribution system which is very different.”
Whether it’s the U.S. or Antarctica they still use wires to make a circuit. They do not rely on ground for a return path, only for safety. Back in the 1800s for telegraph (low current, low voltage) they had used it but switched. Rarely, in extremely high voltage long distance transmission, ground has been used as a return where the resistance of the ground and the current used is relatively small compared to the voltage. It has been tried and kind of works in these special applications. What was being discussed here was a medium voltage neighborhood distribution system where there is a physical wire used as the return and the ground is just part of the protective or safety circuit, not a return path as you indicated in your drawing. If the ground had any typical resistance at all you would never get full voltage to the load.
--- End quote ---
Sigh. . .
I've never said that the earth is routinely used as a path for the return current on low voltage domestic installations. You've has completely missed the point and taken the thread off topic by being the first to mention the distribution transformer. I apologise for making matters worse by replying to you and mentioning single wire earth return, which as you've correctly stated, is only applicable to high and medium voltage distribution.
--- Quote ---Also in your drawing you show a 3-phase system which is mainly used for larger industrial applications and not residential.
--- End quote ---
You're wrong: a three phase system is routinely used both for domestic and industrial distribution in Europe. Single phase distribution transformers are very rare. We don't have many pole mounted transformers either. One three phase transformer will typically serve a whole street or block. In a domestic, single phase setting, every third house in a street might be on the same phase. For example in a street with 9 houses, numbers 1, 4 & 7 might be on phase 1, houses 2, 5 and 8 on phase 2 and houses 3, 6 and 9 on phase 3.
--- Quote ---As far as an isolation transformer working I see that you agree with my previous diagram from post #20 on that point.
--- End quote ---
Yes, it illustrates why a meter will read 230V between live and earth, when connected directly to the mains but will read 0V between the secondary and earth on an isolation transformer. It demonstrates that when the transformer's secondary is earthed, there's a possible return current path through the earth, yet there is none when the secondary is floating. The ground current path is shown between the meter and transformer's earth connection. I repeat it's not supposed to illustrate the correct way to measure the mains, just that the full mains voltage will be present if one of the meter's probes is earthed and the other connected to live. Note that the isolation transformer's primary is connected between live and neutral, not earth!
nForce:
--- Quote from: Shock on December 12, 2018, 09:11:04 pm ---
--- Quote ---So electrons also alternate in the earth, when conducting in the loop?
--- End quote ---
So again defining the parameters, if there is AC voltage potential between two points then you're ready for current to flow. By completing the circuit or loop it will conduct and at the electron level they will alternate directions at the frequency of the mains.
Like I said previously (unless you want to dive deep) just consider the earth to be a wire and if it's in circuit (and not isolated) electricity will conduct.
--- End quote ---
If we take an ampermeter and connect it in the earth let say 10 meters below ground, then we will measure AC current if we have single wire earth return power system?
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