Electronics > Beginners
Isolation transformer and electrons
ArthurDent:
GeoffreyF – “Electrons have no feelings.” GeoffreyF is correct and I have never met an electron that was hell bent on doing me harm and in a one-on-one interaction they cause no problems at all. However, in a large crowd they can do a great deal of harm if you cross them.
:-DD
All these metaphysical descriptions of electrons with ‘free will’ is just confusing the issue. There also seems to be some mystique about isolation transformers where there is no similar concern about step-down and other transformer ratios. You might guess that an isolation transformer does just what it says-isolates. There are also some things that just have to be taken as real and ohms law is one of those things.
Simply put, if there isn’t a complete circuit there will be no current flow. The following modified drawing displays it pictorially.
Zero999:
Oh I see, it seems this is about the common misconception of what ground is, rather than how transformers work.
In order for current to flow, there needs to be a complete circuit. Any electrons coming out of the negative terminal of a battery, must go back into the positive. The same is true for the transformer, except the direction of the current flow is continuously changing.
Another interesting fact is that within a closed circuit, the net charge remains constant. When a capacitor discharges through a resistor, the number of electrons and thus charge in the entire system doesn't actually change. All that happens is electrons are transferred from the negative plate of the capacitor, to the positive plate, via the resistor. The number of electrons inside the capacitor stays the same.
Ground is just a reference point, from where all voltages are measured. It makes no sense to measure the voltage between a stake in the ground and a floating transformer secondary. All you'll read is a ghost voltage, leaking through the transformer's inter-winding capacitance. The primary coil is acting as one plate of the capacitor with the neutral of the mains connected to the soil and the secondary is the other plate of the capacitor. If the voltage source powering the transformer was to be completely isolated from earth, which is actually impossible, as there will always be some capacitive coupling, then you'd read zero between earth and any part of the circuit, because no current would flow.
Shock:
--- Quote from: nForce on December 09, 2018, 06:08:43 pm ---when we have 120 V potential on the top and 0 on the bottom tap. We are standing on the ground which is 0 V. We touch the bottom tap and because it's 0 V, and we are standing on the ground which is also 0 V, there is no current. Now we touch the top tap which has 120 V potential and we are standing on the ground which is 0 V. Now what?
You are going to say, yes there will be no current, because we have isolated system and we don't have a current loop to flow. Ok, but electrons do not know nothing about isolated system, they just see a voltage difference. So we are touching the top tap 120 V potential, and we are standing on the ground 0 V potential.
--- End quote ---
The problem with the question you are asking is you are defining a 0V that does not exist on the secondary side in the circuit shown.
Between L1 and L2 (the secondaries) is the 120VAC difference in potential. Those two connections are no longer Live/Neutral/Earth (or what you want to call them) as they are galvanically isolated.
Ground/Earth to the secondary is just like any other conductor, it might as well be a piece of wire. It's not 0V to the secondary, it's nothing while not connected. While not connected the only situation it would be called it 0V is in reference to the live side if the Neutral is at the same potential as Ground/Earth.
The electrons won't see a voltage difference between the secondary and Ground/Earth because there is none. There has to be some kind of completed circuit in order to induce the flow of electrons.
Shock:
You can find how electrons flow in a circuit in any textbook but going back to your original question of how do they know. A simplified analogy would be how evaporation and precipitation works. This is a completed circuit and has flow (of moisture/water in this case) aided by the warming and cooling of the earth.
If we introduce an insulator and isolate the earth from the sky no complete circuit exists and no flow occurs. There might be plenty of potential to flow in the oceans but without the loop nothing will occur.
nForce:
--- Quote from: Shock on December 09, 2018, 11:02:35 pm ---You can find how electrons flow in a circuit in any textbook but going back to your original question of how do they know. A simplified analogy would be how evaporation and precipitation works. This is a completed circuit and has flow (of moisture/water in this case) aided by the warming and cooling of the earth.
If we introduce an insulator and isolate the earth from the sky no complete circuit exists and no flow occurs. There might be plenty of potential to flow in the oceans but without the loop nothing will occur.
--- End quote ---
If I reference to this picture. Because earth has everywhere potential of 0 V, how do electrons find the correct path through earth to the transformer? If we have a town with 20 transformers, and we create a short circuit somewhere on the grid, how do electrons know where to flow to that one transformer of the total 20?
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