Sorry, I've been careless with my typing again.
That is not one wire carrying 1A, it is the 100-wire bundle, each wire carrying 1A. It would probably try to produce kilovolts if the bundle passed through the core.
As already remarked, the induction from wires outside a toroidal core is insignificant compared with a wire passing through the centre.
-- Tony Williams.
...but very wrong (electrically speaking).
There's no such thing as a partial turn. Think about it. If you have current flow, you have a circuit, which means you have a complete loop (i. e., turn). It doesn't matter much whether the return path is 1/16" away, or 12" away, or 100ft away. It's still a complete loop.
The larger the loop is, the more opportunity there is for parasitics to siphon off some of the field; but the core is generally very high mu, and offsets the parasitics almost completely.
That's why standard current transformers (remember the discussion of a few days ago?) work quite well with just a single cable threaded through the core.
Picture 1 gave a tiny voltage because a tiny fraction of the field passed through the core hole, inducing voltages into the near wires without being cancelled by corresponding induction into the opposite wires on the core.
Picture 2 had roughly equal and cancelling fields inside the hole.
Picture 3 had a slightly higher voltage than 1, probably because the wires were not bent exactly at the same angles, so got a trifle more of the uncancelled field in the hole.
Picture 4 is picture 1 plus 2 copies of picture 2. Same voltage out as 1.
I don't know how many turns you had on the secondary, butput the primary wire inside the hole and the output voltage will be very high if you've wound it at all like a CT (which is what a GFCI or RCD is, after all).
Put the primary inside the hole, loop it back inside again without going around the core, and you'll have zero out. That's a GFCI/RCD.
jp
Think about coils without a core which goes around the wires. Air cores and cores which are like a straight stick.
In all such cases partial turns work exactly as expected. You can use it to fine-adjust the transformed voltage relation to the input voltage.
Toroids are just a special case, which cannot change the basic laws of physics, and cannot change the fact that partial turns give different voltages,
but the partial turns have much less effect in a toroid transformer, because the effect is masked by the strong effect of going through the core or not.
-- Roger J.
Of course. Here there's no closed magnetic circuit to confine the field. There's plenty more leeway for field from one segment of conductor to avoid all other conductors, or cancel from conductor to conductor. There is no such leeway in a toroidal or other closed magnetic circuit.
Actually, no. Toroids enforce the basic laws of physics by not allowing parts of fields to go astray.
Depends upon your point of view :-).
jp
On Tue, 10 May 2005 09:25:05 +0100, Tony Williams put finger to keyboard and composed:
Thanks very much for that.
I guess another way of looking at it is to say that a "turn" refers to the number of times a conductor passes *through* the core rather than
*around* the core.- Franc Zabkar
-- Please remove one \'s\' from my address when replying by email.
Not quite true. Its possible to wind half-turns on E cores, but of course this unbalances the flux in the outer legs, which may cause problems. for example see Billings, Switch Mode Power Supply Handbook section 4.23 - transformer half-turn techniques.
A toroid cannot have half-turns, for the reason John Perry pointed out - current flows in loops therefore the circuit *always* completes a loop around the toroid.
Cheers Terry
On Tue, 10 May 2005 09:25:05 +0100, Tony Williams put finger to keyboard and composed:
Hmmm, that means there must be a net flux equivalent to
7.6mAmpere.Turns. This in turn suggests that a perfectly balanced load current of 100A is creating a core imbalance equivalent to that expected for a leakage current of 7.6mA. I wonder if you now pass a single wire through the core whether an ammeter will measure 7.6mA.- Franc Zabkar
-- Please remove one \'s\' from my address when replying by email.
I'm ok with the series-adding measurements, but would be a little cautious about using the numbers off the series-opposing expt.... there was too much variation across the three conditions. I suspect some other effects are going on.
-- Tony Williams.
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