Talk:Autotransformer

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I read that the new UK 'High Speed 1' rail line from London to the Channel Tunnel uses electrification on the 2 x 25 kV autotransformer system, as opposed to the conventional 25 kV system. Could anyone kindly explain what that means, please? Halibut, October 30th 2007.

An autotransformer is an electrical transformer with only one winding sounds a bit confusing. One winding means one loop of wire in my ears.

I guess it is supposed to be:

An autotransformer is an electrical transformer with only one coil.

Am I right? --Abdull 12:21, 24 July 2005 (UTC)

Your interpretation is correct, but engineers don't use that term ("coil") in that way; instead, they use the word winding. "One loop of wire" is referred to as "one turn", so a winding may have one or more turns of wire.

Atlant 21:27, 24 July 2005 (UTC)

[edit] Diagram

THis diagram appears to be of a variable autotransformer. Should it not be captioned as such?--Light current 20:06, 15 January 2006 (UTC)

Duagram shows only step down operation. Is it not true that auto-transformers can also step up? --Light current 02:32, 16 January 2006 (UTC)

Autotransformers are used for step up, step down or adjust either direction. The pictured variac is connected for 120V input and 0 to 280V output. --C J Cowie 14:05, 16 January 2006 (UTC)

It must be your Variac, otherwise, how could you tell (from that picture)? :-)

Atlant 14:18, 16 January 2006 (UTC)

I suppose you could connect it the other way round, but what I was implying is that auto transformers (variable ones anyway) have an over unity ratio as a max (say 120%) then you can tap all the way down from that thro unity ratio toward zero voltage.--Light current 17:02, 16 January 2006 (UTC)

I think that an over unity max ratio is a common configuration for variacs. Mine, the one pictured, has several fixed taps with a max ratio of 233%. It was originally a 3-gang unit that could be wye connected for 480V use. I "let the smoke out of it" at work and eventually took home a section that I restored to reasonably serviceable condition. --C J Cowie 17:17, 16 January 2006 (UTC)

Yes, lots of Variacs had a tap that allowed a small step-up function; this greatly facilitated their use in testing electronic equipment as you could then easily vary the input mains voltage (to some piece of equipment-under-test) over the entire specified range of operating voltages. I've never seen one that allowed the range that C J Cowie is speaking of, though I have no doubt that they existed.

Atlant 17:22, 16 January 2006 (UTC)

I can redraw it to show some form of overrange capability. BillC 20:22, 16 January 2006 (UTC)

Thats very kind of you to offer to do that BillC . BTW nice selection of variacs here [1]:-)--Light current 21:50, 16 January 2006 (UTC)

Well, I did it. I'm not altogether convinced that the new one is clearer than the old, but the SVG image is uploaded to the Commons under GFDL, so if anyone want to pick it up and edit themselves, they can do so. BillC 23:19, 20 January 2006 (UTC)

I think the new diagram looks great. Very clear and obvious. Thanks BillC!--Light current 23:36, 20 January 2006 (UTC)

what about efficency? is it suitable for high power applications? what disadvantages has it over normal transformers?

[edit] Proposed merge

I placed the merge tags on this article and Buck-boost transformer. A buck-boost transformer is a specific type of autotransformer. Although a buck-boost transformer may use a transformer with multiple windings, they are connected together electrically to form an autotransformer. I think the buck-boost transformer article could be covered with a section in this article. Please post comments below. Thanks. HeirloomGardener 21:53, 18 May 2007 (UTC)

Please see discussion at Talk:Buck-boost transformer. Decision was to not merge. HeirloomGardener 22:30, 20 May 2007 (UTC)

[edit] Equations

Surely there should be some transformer equations so that an autotransformer can be compared to a normal tranformer? Thanks PaulE