On Wed, 29 Sep 2004 20:27:26 -0500, Jim Adney
wrote:

On Wed, 29 Sep 2004 12:13:11 -0500 John Fields
wrote:

I disagree. Using EI laminations and winding the entire transformer on
the center leg, it makes nore sense, if only for the sake of economy,
to wind the CT primary bifilar and avoid using more wire than
necessary. After all, an extra ten feet per transformer is about two
miles of wire, 1000 transformers downstream. Putting down both halves
of the primary at the same time also saves time and tends to make both
halves of the primary look more alike than winding one half on top of
the other.

I think this is only half right. Winding them bifilar would certainly
make them more "balanced" in both turns and impedance, but the total
amount of wire used would have to be the same.

---
You're right.
---

Think of it this way: I still need the same number of turns in each
winding and the same number of total turns. Winding them bifilar
(assuming the same wire gauge) will still occupy the same amount of
the winding window.

So instead of "an extra ten feet" of wire in the outer winding, we end
up using five extra feet in each winding.

---
I'm not sure I understand what you mean unless you're referring to the
penalty for not having two separate windings.

To find out I set up a hypothetical situation using wire with a
diameter of 0.1", a length of turn of 1" for the first layer and a
window width of 2" in order to get 20 turns per layer, and using
either bifilar winding or one winding on top of the other, for 10
layers the total length of wire was 765.3". For the bifilar case,
each winding's length was 382.65", but for one winding on top of the
other, the shorter winding was 225.58" and the longer winding 539.72"!

Taking the total number of turns per winding (100)and winding them
separately would require twice 225.58", or 451.16". Since either the
bifilar or "conventional" winding would require 765.3" for the same
number of turns, that's a savings of 314.14" of wire!
---

I don't know how a real transformer manufacturer would look at it, but
I suspect that the bifilar way has real appeal as long as the voltages
are small.

Once the voltages are large, we may want to spread out the ends and
wind them separately, which most likely means that we're back to the
original method of one on top of (and longer than) the other.

---
Dunno...


--
John Fields