| Electronics > Beginners |
| Isolation transformer and electrons |
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| nForce:
--- Quote from: Shock on December 12, 2018, 04:36:00 am --- --- Quote from: nForce on December 11, 2018, 07:24:41 pm ---Yes, so the electrons are switching between earth and the wire, and between earth and the transformer. But my point was about the earth (planet). --- End quote --- The earth as a whole is considered neutral. It has the ability to conduct (and alternate) electricity in a completed circuit. Though not the most reliable conductor of electricity which is why ground/earth rods are sunk into favorable conditions depending on the soil type, moisture, depth. There is actually a high voltage transmission line system called "Single Wire Earth Return" which just uses one conductor and the earth to complete the circuit over long distances. As mentioned, the Neutral side of the mains is connected to Earth throughout the distribution network at various points (at least here it is). Because the mains is now Earth referenced (not floating) making a connection between Live and Earth to complete a circuit will cause electrons to move back and forth like I showed in the previous image. How far do the individual electrons travel in a Live to Earth circuit? Not very far at all, they would alternate similar as with wires given the same propensity to conduct. Do they still alternate in the ground, earth, soil? Yes where it's conducting and not 100% insulating. What path do they take to complete the circuit? The majority would be "shared paths" of least resistance to the nearest neutral line I would imagine. Perhaps there is also some capacitive effect as well, I'm not sure. But we know electrons alternate through conductors, even poor ones. They tell us this at school :). --- End quote --- So electrons also alternate in the earth, when conducting in the loop? |
| Zero999:
--- Quote from: ArthurDent on December 12, 2018, 02:43:20 pm ---Hero999 – “In the distribution transformer scenario, the earth simply acts as a return conductor for the current path. If one side of the transformer isn't connected to earth, then there will be no return current path, so no current will flow, as is the case with the isolation transformer, when the other side isn't earthed.” That is absolute incorrect. If you had read my post #27 and post #30 you would know that the earth grounding of the neutral wire (that is the actual return conductor for the current path) is a safety feature and the earth isn’t relied on for carrying current. The reason for this is simple, the earth’s resitivity is a variable that varies wildly from fairly low in some areas to near infinity in rocky areas. Power distribution has to be known and controlled and utilities can’t have one customer’s lights dim or flickering while the neighbor’s lights are very bright. Two wires are used and ground is only a safety connection. --- End quote --- I'm aware of that. I did read your posts, but they refer to distribution transformer, rather than the original poster's set-up. The original poster is also in Europe and you refer to a US distribution system which is very different. Yes, the earth can act as a current return path. In most installations, the neutral conductor should only be intentionally used as a return current path, but the earth is a common return path, under fault conditions. Note that in some installations, the earth is indeed the sole path for the return current. https://en.wikipedia.org/wiki/Single-wire_earth_return What I was attempting to explain was that in the case of an isolation transformer, the secondary is not connected to earth, therefore there is no return path for the current, via earth. If a meter were connected from anywhere on the secondary to earth, it will ideally read 0V. In the case of a distribution transformer, the secondary is connected to earth, so connecting a meter between the live and earth would result in the full supply voltage being read. |
| ArthurDent:
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. Also in your drawing you show a 3-phase system which is mainly used for larger industrial applications and not residential. Even with that, the assumption of ground being the return path is incorrect. Here is how it is described: “Wye vs. Delta Connections Starting with Wye, the connection consists of a total of five wires: (3) hot, (1) ground and (1) neutral. The configuration closely resembles a letter Y, with the neutral component connected at the middle, which is also where all the lines converge. It is at this point wherein the voltages are all equal. It is important to point out that the phase and line current are also considered to be equal. Multiplying the phase voltage by 1.732 (or square root of 3) will result in arriving at the voltage present between any of the two lines. In a Wye system, 120V can be measured from any hot wire to neutral. Additionally, 208V is measured from hot wire to hot wire. This is also the same for Delta configurations. By comparison, a Delta circuit inside a transformer appears as a triangle with equal sides, resulting in a closed path. In most cases, such wiring configurations do not have a neutral and is present on the secondary side of the transformer. The three phases are connected at every meeting point on the triangle. Moreover, a Delta system is equipped with four wires: (3) hot and (1) ground.” Here is an excellent video from ElectroBOOM that cover a lot of the points discussed, both 3-phase and single phase, and makes it clear. I recommend his videos because they also have entertainment value while showing the pitfalls of doing it wrong. As far as an isolation transformer working I see that you agree with my previous diagram from post #20 on that point. |
| IanB:
ArthurDent, you seem to have completely missed the flow of the thread and the context in which answers are being provided. It's also a bit silly and condescending for you to be trying to correct someone (Hero999) who obviously would not make the mistake you are implying. Let's be clear here: the earth acts as a return conductor for the current flowing through a person standing on the ground who touches a hot wire. If the transformer neutral wasn't grounded at one or more points along the way, the earth would not act as a return path to that transformer. The misconception that seems to arise from the OP, as much as we can try to understand it, as that somehow the earth/ground is a magical 0 V sink for all voltages anywhere. This is not true. The ground only acts as a magical 0 V sink in as much as it acts as a return path for current back to a source that has a grounded neutral conductor. |
| Shock:
--- 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. |
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