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This YT video (scrolled to 0:45) shows the process of fabricating a pole mount transformer. At 0:45 the following is shown: there's a wooden brick used to hold everything together, it's covered in cardboard and then the person starts winding wide thick aluminum tape onto this brick. Aluminum tape is as wide as the brick, so the brick is effectively wrapped into multiple layers of that tape. Adjacent layers are separated with thick insulating paper.

The core is fabricated much later, so it's not the core.

What's that tape for? It's thick so I'd guess it's the secondary winding (low voltage, high current, lots of heat) but then why is it closest to the transformer center where it's harder to get it cooled? Also I've disassembled a number of different transformers so far and I've never seen wide tape being used as a winding wire so I'm not at all sure.

What is this tape? Is it the secondary winding? Why is it closest to the transformer center?

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    \$\begingroup\$ Let the video run for a few more seconds and they tell it... \$\endgroup\$ – PlasmaHH May 26 '15 at 13:50
  • \$\begingroup\$ @PlasmaHH There're lots of words there - some busbar, low voltage leads are mentioned, high voltage is mentioned - all over the course of the several seconds while the tape winding process is being shown. \$\endgroup\$ – sharptooth May 26 '15 at 15:15
  • \$\begingroup\$ Even if you don't connect these words into sentences, what could these low voltage leads (that are evidently connected to the aluminum tape) that sends low voltage out from the transformer possibly be? \$\endgroup\$ – PlasmaHH May 26 '15 at 15:37
  • \$\begingroup\$ @PlasmaHH Well, I would guess that it is the secondary winding but first, I've never seen a winding made of such thick tape, and second, I'm surprised to see the secondary being the closest to the center. Btw I outlined all these concerns in the question. Yes, I realise that my question may sound a bit dumb but because I'm not an expert in transformers fabrication all of this is not really obvious to me. \$\endgroup\$ – sharptooth May 26 '15 at 17:26
  • \$\begingroup\$ I am by no means a transformer expert too, but when you wrap something that provides low voltage and high current around the core of a transformer, really, what else could it be? Buried as a side note here is a possibly intresting question though: why is the low voltage inside and the high outside... \$\endgroup\$ – PlasmaHH May 26 '15 at 21:37
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I didn't watch the video, but wide and flat metal is sometimes used in high-current transformer windings.

I suspect aluminum is only to save cost over copper. Copper has lower resistivity, but aluminum is also pretty low. You need a bit more aluminum to counter the higher resistivity, but this is still cheaper than the lesser amount of copper.

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