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How a pole transformer is made

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Renesis

Tue Apr 14 2009, 04:30PM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

Its from the "How its made" program on discovery.

They have always been so good to explain... Tell me, what is the purpose of that aluminium sheet? Is it the low voltage winding? At least im sertain that they dont select aluminium because it "withstands the heat that a high voltage current produces"

Im a little confused on how these are wired. It seems to me there is only one high voltage connector, and a three phase low voltage output?

And what is "electrical steel"?

Plasma Lover

Tue Apr 14 2009, 04:55PM

Registered Member #1911 Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165

Electrical steel would, most likely, be the steel plates rather than a single block of steel, which wouldn't allow the current to flow as smoothly and would end up being saturated easily. The aluminum sheet may be useful because of the heat conductance properties, seeing as it is a good heat conductor, but, in that case, why not use copper? It's not much more expensive and has much better heat conductance qualities. This one I'll leave for an engineer that works with transformers on a regular basis.

Fraggle

Tue Apr 14 2009, 06:31PM

Registered Member #1526 Joined: Mon Jun 09 2008, 12:56AM
Location: UK
Posts: 216

The aluminium strip was certainly the low voltage winding. They probably mean silicon steel I guess.

Myke

Tue Apr 14 2009, 11:03PM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

Plasma Lover, are you talking about the core? Isn't the core just made of sheets to reduce the losses of eddy currents?

Plasma Lover

Wed Apr 15 2009, 12:46AM

Registered Member #1911 Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165

Myke wrote ...

Plasma Lover, are you talking about the core? Isn't the core just made of sheets to reduce the losses of eddy currents?

Ummmm....yes. You're right.

Wow. I am quite embarrassed, now. Thanks for the correction. The gap in the core is used to prevent saturation.

Although, wouldn't the eddy currents result in loss of energy and excessive heating, just like saturation?

Dr. Slack

Wed Apr 15 2009, 07:22AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

The aluminum sheet may be useful because of the heat conductance properties, seeing as it is a good heat conductor, but, in that case, why not use copper? It's not much more expensive ...

... but it *is* more expensive, aluminium has a better conductance (both electrical and thermal) per unit cost, especially in sheet rather than wire form. Copper is easier to make into wires, to solder to, and is better per unit volume, so is the material of choice for small transformers. As well as best per unit cost, alli is also best per unit weight, so if you are not particularly constrained on transformer size, and want to use the smallest bolts when you hang it from a pole ... Then there's the supply and scarcity issue.

Bear in mind that almost all decisions made about manufactured items come down to cost first, physics second. We'd use silver for wires if we wanted the best conductance per unit volume, but copper is much cheaper. I'm not certain why alli isn't used more in mid-sized transformers for wire, perhaps it's the volume economics of the infrastructure - like copper wire is made by the gazillion miles and sheet is rare, alli wire is rare but the sheet is common. Maybe most transformers can't take the hit on volume (real estate is expensive) unless they're hanging from a pole.

The gap in the core is used to prevent saturation.

No, any transformer will be as gap-free as econmonically possible. Saturation is prevented by choosing a high enough turns per volt. Gapped cores are used in inductors to increase the primary current required to reach saturation, an effect not wanted in ideal transformers

And what is "electrical steel"?

"Electrical steel" is steel that works well in transformer cores, so low cost, low hysteresis loss, high permeability, high resistiivty - and more or less in that order of importance. The addition of silicon to low-carbon steel both increases the resistivity and reduces the area of the hysteresis loop. Cold rolling and heat treatment is also used to improve the magnetic properties, often preferrentially in the direction of rolling

Cesiumsponge

Wed Apr 15 2009, 12:17PM

Registered Member #397 Joined: Wed Apr 19 2006, 12:56AM
Location: Western Washington
Posts: 125

Plenty of high voltage power components use aluminum because of cost. Electrical power transmission lines are stranded aluminum or stranded aluminum over a steel wire rope core. Right now, copper's spot price on the base metals market is 319% more than aluminum.

Renesis

Wed Apr 15 2009, 01:27PM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

Wow, thanks for all the replies. But im still confused on how these are internally wired. Not that it really matters, im just curious.

3l3ctrici7y

Wed Apr 15 2009, 05:58PM

Registered Member #1806 Joined: Sun Nov 09 2008, 04:58AM
Location: USA
Posts: 136

You are wondering about the three terminals on the side wall that the aluminum straps connect to?
I think that is the 240v output, with the center tap, so that you can get two phases of 120v, or play the ends off of eachother and get 240v.

Arcstarter

Wed Apr 15 2009, 06:00PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Renesis wrote ...

Wow, thanks for all the replies. But im still confused on how these are internally wired. Not that it really matters, im just curious.

Wired? As in... how? How it is hooked to the bushings? XD

Aluminum is what is used in modern day iron core MOTs, at least most of them. This is NOT a good thing for the experimenter, because we usually push to the very limits. Aluminum is light and cheap, BUT it DOES have higher resistance. This means more primary heating. There is also skin effect and other stuff, but i am unsure about how it effects it.

Also, in televisions around the CRT they use that 'thick wire' that surrounds the CRT, which is insulated in none other than electrical tape. Take the tape off, and it is (for a large CRT) hundreds of feet of wire! BUT, this is also aluminum from the wire that i have seen. MOTs and TV's use so much wire, they just use aluminum to cut down on cost, while till working alright.

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