Electronics > Beginners
Isolation transformer and electrons
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Zero999:

--- Quote from: nForce on December 13, 2018, 08:13:28 pm ---Why didn't you tell me about this at the beginning?

It took 3 pages of this topic just to explain to some beginner that yes an AC current flows in the earth because of the power grid and it's called a stray current.

I didn't know about this, because in convential circuits there is always a return wire. The earth does not look like a wire.

--- End quote ---

Why did it take three pages for you to make it clear what you were asking?

Go back to your original post.

--- Quote from: nForce on December 02, 2018, 05:45:22 pm ---I have a basic question:

When we use isolation transformer we have a physical electric isolation between two systems. If we connect a wire between a system on the other side of an isolation transformer and ground then the current would not flow.

But how do electrons know on the other side of an isolation transformer that we don't have a current loop? They just feel a potential difference, so they should flow because they don't know nothing about isolation.

Thank you.

--- End quote ---
How was anyone supposed to know you were asking about stray currents? All you talk about is an isolation transformer and electrons?

Consider being more descriptive and posting some schematics, rather than a few cryptic statements.
IanB:

--- Quote from: nForce on December 13, 2018, 08:13:28 pm ---Why didn't you tell me about this at the beginning?

It took 3 pages of this topic just to explain to some beginner that yes an AC current flows in the earth because of the power grid and it's called a stray current.

I didn't know about this, because in convential circuits there is always a return wire. The earth does not look like a wire.

--- End quote ---

Except...


--- Quote from: IanB on December 11, 2018, 09:08:39 pm ---Now imagine the Earth as a big ball of wire floating in space.

The current flows through you, through the Earth (a big ball of wire), through the rod in the ground, and back to the transformer.

--- End quote ---
Brumby:

--- Quote from: nForce on December 13, 2018, 08:13:28 pm ---Why didn't you tell me about this at the beginning?
--- End quote ---
As already stated - but I will rephrase:  To get good answers you need to ask good questions.  We aren't mind readers and if all we know of you is what is in one or two posts, then we need you to help us understand exactly what it is you are asking.


--- Quote ---It took 3 pages of this topic just to explain to some beginner that yes an AC current flows in the earth because of the power grid and it's called a stray current.
--- End quote ---
That is a rather simplified statement and not properly qualified.

Stray currents are unintentional, but occur as a function of the physics of a situation.  Fault currents are caused by a safety earth at the customer's location having a path to Live.  In a single wire earth return system the current through the ground in normal operation is, by design, the full current of the load.


--- Quote ---I didn't know about this, because in convential circuits there is always a return wire. The earth does not look like a wire.

--- End quote ---
You are being too literal.  The Earth may not look like a wire, but it certainly DOES look like a conductor when you look at it properly - and this is the trick in understanding a few things with electricity ... what is a conductor may not seem like it should be.  Breathe on a high impedance circuit and the moisture that condenses from your breath will affect that circuit.  The human body does not look like a wire, but it conducts electricity - just hold the probes of your multimeter while on a resistance range.  This is also why electrocution is a risk.
nForce:
Ok then, thanks for your help.

I have one question: Our electrical outlets at home are voltage sources. Because the voltage is constant and the current varies. But what are limitations that outlets would be current sources?
Zero999:

--- Quote from: nForce on December 14, 2018, 06:17:31 pm ---Ok then, thanks for your help.

I have one question: Our electrical outlets at home are voltage sources. Because the voltage is constant and the current varies. But what are limitations that outlets would be current sources?

--- End quote ---
With a constant current source, the loads would need to be connected in series, for the current to be constant. If the loads were connected in parallel, the current would vary, depending on the loads, similar to connecting devices designed for operation off a constant voltage source in series. The open circuit voltage of a constant current source is theoretically infinite, with the power being proportional to the resistance, so open circuits need to be avoided and rather than disconnecting a load, it should be replaced with a short circuit, which will result an relatively little power dissipation.
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