Talk:Transformer/Archive 2

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Archive This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

Contents

Transformer shortcircuited even at AC?

The article says: A transformer winding should never be energised from a constant DC voltage source, as this would cause a large direct current to flow That is totally clear to me.

When thinking about AC on a transformator, i still think of a shortcircuit - how can it be, that there are still 98 % of the energy transported on the "other side" rather than just flowing through the first coil and therefore shortcircuiting a current source or voltage source.

Still, when to do say a current being DC, and when AC? Is it still OK to use a AC of 0.00001 Hertz (that is around one revolution per day) on a transformator? --Abdull 13:00, 24 July 2005 (UTC)

That's a good question. To answer it, let's go back to first principles. Take a transformer, and remove the secondary winding (or, equivalently, just leave it open-circuited). You now have a single winding, the primary, wrapped round an iron core - in other words, an inductor. Now connect that inductor to a DC voltage source. As with any inductor, the current will start at zero and rise linearly with time. Most of the energy goes into building a magnetic field in the core, and just a little goes into heating the wire through resistive heating. After a while, the core will become saturated - that is, it can't contain any more magnetic energy. At this point, the device stops being an inductor, and all you have left is the resistance of the wire. You now have a low-resistance piece of wire connected across your DC voltage source, so a large current flows and the wire gets hot. This is a bad thing to do to a transformer, and will probably destroy it.
For our next trick, let's repeat the experiment (assuming the transformer is still in one piece), but using an AC voltage source instead of DC. This time, the magnetic field builds up for one half-cycle of the AC waveform, but then decays to zero and starts to build up in the opposite direction for the second half-cycle. Because the AC voltage keeps reversing, the magnetic field repeatedly builds to a finite value and then decays. If the frequency is high enough, the magnetic field will never reach its saturation value and the core will always behave linearly. If the frequency is too low, then the core will saturate before the end of the first half-cycle, and the wire will get hot. The limiting frequency depends on the construction of the transformer and the size of the AC voltage. Roughly speaking, if you halve the frequency, then you must also halve the voltage rating of the transformer primary. --Heron 15:01, 24 July 2005 (UTC)
So just to drive that point home, if the transformer has enough inductance, then it will work at that 8.64 cycles/day frequency that was being discussed. But it would require an awfully large amount of inductance (so many, many turns around an enormous core). But if it could be manufactured, it would work.
Atlant 21:20, 24 July 2005 (UTC)
Stupid transformer trick: if a small transformer can step 120 VAC down to 12 VAC, can't I just connect the low side to 120VAC and step it up to 1200 VAC? WRONG! Typical result: smoke, circuit breaker trips, fuse blows etc. I learned this the hard way when I didn't understand core saturation. Madhu 19:05, 2 September 2005 (UTC)
Yes you need to be careful if connecting transformers the wrong way round (despite what many books say). You must have enough turns on the 'primary' (enough inductance) to avoid core saturation. Light current 13:16, 3 September 2005 (UTC)

explosions

I don't want to be sensationalist, transformer explosions are rare, but maybe their should be something about them in this article. There was recently a large explosion in SF. [1]

I think this would be a worthwhile addition (and I assume it mostly happens when water gets into the coolant and breaks down its insulating capability). We are starting to get to the point, though, where we might want to factor "utility transformers" (or something) out of this article into their own article.
Atlant 00:26, 22 August 2005 (UTC)
Distribution Transformers do occaisionally blow up. This is probably due to bad maintenance. Water in the oil or discharge damage in the windings, bushings etc. Large HV transformers have to be looked after! Light current 13:25, 3 September 2005 (UTC)
Scotty

Losses

Any one know what inductance and capacitance in transformer windings have to do with losses? This is another new one on me!--Light current 13:35, 11 September 2005 (UTC)

  •  :Light current
  •  :Please be advised: There is a thing called Reactance (X sub l)and not to mention Harmonics. High wattage transformers.
  •  :Reactance = 2 (pie) fl

and the seventh Harmonics on an electrical transformer is a killer.

  •  :Scott 17:37:46, 2005-09-11 (UTC)

Reactance does not cause losses. Only resistance causes loss. The statement is inaccurate.--Light current 17:42, 11 September 2005 (UTC)

  •  :Light current
  •  :Please tell me your definition of reactance here. Possibly my confusion between Impedence Please do clarify for me. Thanks Scott 18:03:23, 2005-09-11 (UTC)

Just click on reactance, my friend!--Light current 18:09, 11 September 2005 (UTC)

  •  :Light current
  •  :Ah so, if Reactance in a transformer is a direct and propotional relationship of impedance (load or no load), see formula you dircted me to, then there has to be a direct relationship of some type of loss or resistance/ impedence in a transformer? Have to run Scott 18:38:15, 2005-09-11 (UTC)

Well, usually to get more inductive impedance (Xsubl) you put more turns on the core. This would necessarily increase the winding resistance and therefore the losses (probably). The extra inductance will just reduce the magnetising current a bit but not cause any losses in itself.--Light current 18:49, 11 September 2005 (UTC)

Light current,
I agree that because of reactance, losses does not occur. But If you see power traingle, As reactane increases,phase angle increases by that power factor decreases. Having low power factor means as compared to capacity of the device (i.e. MVA capacity of transformer)you are using less power(i.e. actve power or MW) It says that efficiency of the device is less.
secondly,as per my knowledge,we donot increase number of turns for reactance increament but to get appropriate voltage. Voltage increases,but as power (ie.MVA) is constant (for given transformer)current reduces.

power = V * I. So that ultimate increament in resistance losses is not much. ---Shilpa.Choudhari 06:19, 9 December 2005 (UTC)

Pictures

Do we really need two pictures of essentially the same thing (laminated core transf) in the article. I think one would do. Any comments?--Light current 17:45, 15 September 2005 (UTC)

  •  : Up to you, light current, it's there for now as a contribution and its heavy duty. Scott 19:08, 15 September 2005 (UTC)

Scott, I propose to delete the lam core power transformer because we dont need two pics and the other pic shows the laminations more clearly(ie its a better photo.) Sorry, nothing personal!--Light current 04:46, 30 September 2005 (UTC)

Not a problem here old man Scott 02:09, 5 October 2005 (UTC)

Large (MVA) Transformer Pic

Lightcurrent do you not think the big transformer pic is too big? Just got out of jail. LOL Scott 01:16, 1 October 2005 (UTC) This one Is this where you want the text for discussion? I hope I'm writing in the right place. Let me know. Getting late here, I'll check back wit ya tomorrow. Scott 01:58, 1 October 2005 (UTC)

Best to talk on talk:transformer really. Sorry I thought you meant the small lam core one. Well I think the large 13.8 kv is such a good picture, thats why I increased it but feel free to reduce it slightly if you like. Welcome out of the cooler!--Light current 16:36, 1 October 2005 (UTC)

Split article

What is the general consensus on forking off some of this article to Transformer (component) as was done with Capacitor and Capacitor (component)? DV8 2XL 19:11, 5 December 2005 (UTC)

Could you outline your reasoning please?--Light current 01:15, 6 December 2005 (UTC)

"We already have a page called capacitor (dealing with it as a circuit element) which was getting too big- hence the earlier split. I believe the is a 'see also' on the capacitor page if people want to learn about practical capacitors. Searching for capacitor will take you to the a page about the capacitor circuit (theoretical) concept. I see no problem with how its arranged at the moment - but feel free to suggest alternatives.--Light current 13:25, 3 December 2005 (UTC)" Ring a bell? DV8 2XL 01:35, 6 December 2005 (UTC)

You dont need to quote me - just tell me your reasons! ;-) I assume you think the page is to big? I dont happen to agree with you in this case since transformers do not have as many off-the-shelf variations as capacitor components do! I think splitting would destroy the integrity of the message- but please try to convince me otherwise- Im always open to a good argument!--Light current 01:40, 6 December 2005 (UTC)

I apologise.But it was too tempting to pass up! Several (valid) reasons: this article has been tagged 'too technical'; this would give us a chance to deal more on the practical applications and sill permit this entry to grow on the theoretical side. Also, I beg to differ: there are many types of transformers doing all sorts of tasks. Finally the new article can be formatted in such a way that some discipline can be encouraged when the inevitable listing starts to occur. DV8 2XL 01:58, 6 December 2005 (UTC)

Possibly! I will think about it!--Light current 02:09, 6 December 2005 (UTC)

Image removed

This image is from the from a wellknown site ... with alil text added to it .... Image:Transformer.jpg ... ripped off of http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/transf.html ... Sincerely, JDR 21:53, 5 December 2005 (UTC)

Removed inferior PMT picture as we dont need three of the same. We dont even need 2!--Light current 20:04, 24 December 2005 (UTC)

Proposed new structure

The structure of this article seems to me to have grown somewhat unwieldy. I've placed a proposed restructure in the article space for comment. For the most part, the changes are simply shunting around sections of text, though I have deleted a couple of sentences which I thought extraneous, plus one of the pole-mounted autotransformer images. I also slightly reduced the size of a couple of the wider images. For the time being, I have commented out the two circuit symbol tables, since I couldn't immediately see where to place them. At the least, I think they could be combined into one in order to compact things a little. --BillC 19:34, 28 December 2005 (UTC)

Transformer diagram

I think the text for primary and secondary current in the first diagram could do with enlarging to make it easier to see.--Light current 02:15, 29 December 2005 (UTC)

Transformer images

I think that Image:Polemount-singlephase-closeup.jpg is the best image of that type that I have seen in the article.

I would delete from the caption: "in a rural setting." I assume that it is an oil-filled transformer and would suggest adding that. It would be nice to have, in addition, an image of a 3-phase dry-type transformer with the cover removed to show the core and coils. --C J Cowie 15:46, 29 December 2005 (UTC)

Yes, I agree its superb. We'd all like a nice picture of the insides of a largish power transformer-- but where to get one?--Light current 17:12, 29 December 2005 (UTC)

I will see what I can find. --C J Cowie 17:43, 29 December 2005 (UTC)

I'll have a rummage around too. I used to do investigative analysis on three-phase transformers in the 240-800MVA range. --BillC 19:04, 29 December 2005 (UTC)
Thats good. but well need to have a copyright free version dont forget--Light current 19:09, 29 December 2005 (UTC)

Just a little concern about the placement of images in the article. As it stands, we have three images close after one another in the the practical considerations section. Nothing wrong with the pictures, but the article has large blocks of text without any images and the text surrounding the images isn't pertinant to them. Can we take steps to (a) space out the images throughout the text, and (b) place them within sections of text that relate to them? Thanks, --BillC 23:40, 29 December 2005 (UTC)

Yes no problem, be my guest--Light current 23:41, 29 December 2005 (UTC)
Anyone got a better image of transformer internals than the one we have?--Light current 18:58, 12 January 2006 (UTC)
If someone can find a suitable photo, I might be able to produce something similar to what has been done at the top right of Mouse (computing). BillC 19:21, 12 January 2006 (UTC)
There are many good photos on the web, but all copyrighted. If you did this diagrammization (for want of a better word) would there be any copyright restriction regarding the photograph from which it was copied?--Light current 23:19, 12 January 2006 (UTC)
The one that I uploaded is the best I have of 3-phase transformers. I have a variety of small single phase transformers that I could photograph, but I think that they are all similar to the one that shows the laminations. -C J Cowie 19:41, 12 January 2006 (UTC)
The photo copyright would still belong to the original owner, unless it was released under some appropriate licence. It might be possible to contact the owner and ask for a release, though. I think an example of what we might be looking for is here: [2] BillC 23:44, 12 January 2006 (UTC)
Yes I really like that diagram especally if it were a bit bigger!--Light current 23:49, 12 January 2006 (UTC)
Yes, I think the internals of a large 3 ph trans would be good. If there are no copyright problems, then I feel User:BillC's kind offer could sove the problem. I think a good couple of eyepopping diagrams at the head of the article will go a very long way to selection as a featured article.--Light current 23:23, 12 January 2006 (UTC)
Here is a small 1-phase transformer: -C J Cowie 20:55, 12 January 2006 (UTC)
Incidently, the idealised single-phase transformer diagram is a WP:FP candidate, after it was modestly self-nominated by me. (I would ask that no-one from here goes over there and votes though, since this message would look like I'm attempting to spam the vote process). BillC 23:44, 12 January 2006 (UTC)
It's not spamming if you tell them about vote and ask to vote if they like the image. Nikola 08:58, 16 January 2006 (UTC)

Basic principles

Flux coupling

The word "some" bothers me in the sentence "In this way, some of the electrical power fed into the primary winding is delivered to the secondary winding." With 50 & 60 Hz transformers, most of the power is transferred from primary to secondary. With 400 Hz transformers, the losses are higher, but most of the power is transferred. At some higher frequencies, it is probably true that only some of the power is transferred. --C J Cowie 16:10, 29 December 2005 (UTC)

Yeah. Lets delete the word some. It will only confuse the innocent!--Light current 17:06, 29 December 2005 (UTC)

Classification

For consideration:

Power transformers

Either single phase or three phase
Either isolating or autotransformer
Either dry-type or oil filled
Special types
Variable transformers (I think this term applies only the sliding contact type. I don't think it is used when the ratio is changed in steps even if there is a tap changing device that permits changing ratio without rewiring.

Signal transformers

Either air core or iron core (aren't all solid cores iron or material containing iron?)
Either audio frequency or radio frequency with a gray area in between

Special types

Resonant (can be either power or signal)
Instrument (power to signal transducer)
Pulse (can be either power or signal)

--C J Cowie 02:43, 30 December 2005 (UTC)

Yes... and what?? Are you suggesting a page split by any chance??--Light current 02:49, 30 December 2005 (UTC)

I was thinking of reorganization. I think that some improvement in organization is needed. Organization by classification might help. By page split do you mean two or more articles? Is the article too long? --C J Cowie 03:05, 30 December 2005 (UTC)

Well since it has recently been substantially changed by User:BillC and we have new photos, I thought we might give it a rest for a while. But why dont you try to rough out a new page layout in your sandbox and then post it on talk:transformer before going further. Your idea will involve a lot of work and Im not sure the page is really that large at the moment to warrant it. But hey-- be bold! Why not?

--Light current 04:22, 30 December 2005 (UTC)


Analogies

moved from User talk:Light current

A gearbox would imply a speed or frequency change. I think a lever is a closer analogy. See here and here, for example. Regards, --BillC 00:35, 9 January 2006 (UTC)

Gear box changes the speed (equiv to voltage), current (equ to torque) and impedance (equiv to gear ratio). The example you quote is one of a rectilineal transformer but for this to be the correct analogy, it would requre 2 lever arms and three pivots. The gearbox analogy, by contrast, only requires two gear wheels and is therefore more accurate and simpler as an analogy. Refer to Dynamical Analogies, H.F Olson, pub van Nostrand 2nd ed 1958, Lib of Congress Cat card No 58-14102, p95.--Light current 00:50, 9 January 2006 (UTC)
A gear box analogy explains nothing to the article readers. The reader may think a gear box is like a transformer because it's a green-painted metal box full of oil that makes noise when it's working. A "dynamical analogy" is OK for an engineering student already familiar with notions of speed, torque and power and who actually *can* comprehend the relationships with electrical quantities...but we're not aiming at engineering students in this article. Either write up the analogy properly or else leave it out. --Wtshymanski 18:46, 10 January 2006 (UTC)
Alrighty then. YOU & try to satisfy the plea (quoted below) of an innocent reader:

This article is too technical to the lay man, making no effort to explain to those unfamiliar with electronics what a transformer is and does, or even how it works. I suspect that many who've read this have become lost in a sea of technical terms in an attempt to garner some intelligable information, and have probably given up trying. Learning about the meaning of each and every single term and word used on this article is a pointless waste of time and energy if all that's needed is a simple explanation of the JOB and PURPOSE of a transformer, and possibly a few words on how they work - this explanation should be understandable with a bare minimum knowledge of basic electronics. This can be added at the beginning as a "basic explanation" or added alongside each section to clarify.

As youll see in the hist, this was changed from a lever analogy put in by someone else. Ill leave it to him to expand on my replacement analogy.--Light current 22:21, 10 January 2006 (UTC)

This, unfortunately, I feel I am unable to do. --BillC 23:18, 10 January 2006 (UTC)

OK we leave it to others to decide on whether an analogy is required to hlep make the transformer more understandable.--Light current 23:24, 10 January 2006 (UTC)

The analogy section is much better but still disappoints me...and what's a "two wheel" gearbox? --Wtshymanski 04:01, 12 January 2006 (UTC)

Rather than critisice my efforts, why dont you try to improve them?--Light current 04:17, 12 January 2006 (UTC)

Because the particular analogy of a "gearbox" is a rubber crutch at best and the only way to improve it is to remove it. There's a perfectly good explanation in the article. --Wtshymanski 23:38, 12 January 2006 (UTC)

Not according to some readers pleading for simple explanations.--Light current 23:52, 12 January 2006 (UTC)

I see the analogy got fixed again. Tricky things, analogies...better to learn the physics. --Wtshymanski 19:01, 20 February 2006 (UTC)

Litz wire references

1. Rauls, M.S.; Novotny, D.W.; Divan, D.M.; Bacon, R.R.; Gascoigne, R.W., "Multiturn high-frequency coaxial winding power transformers," Industry Applications, IEEE Transactions on , vol.31, no.1pp.112-118, Jan/Feb 1995

Abstract
Previous papers on coaxial winding transformers have focused on designs that use a copper tube to form a single-turn outer winding, and litz wire for a multiple-turn inner winding. In high-power applications, the increased resistance of a solid outer winding due to skin effects can be a limiting factor in achieving good performance, especially at frequencies above several hundred kilohertz. A single-turn outer winding leads to large core cross section areas at lower frequencies and the turns ratio is limited to a ratio of n:1, where n is an integer. This paper demonstrates several methods for achieving multiturn outer windings to improve design flexibility for the coaxial winding power transformer. Experimental measurements on transformers that have multiturn outer windings are included to confirm analytical results and demonstrate the modified designs

2. Odendaal, W.G.; Azevedo, J.; Bruning, G.W.; Wolf, R.M., "A high-efficiency magnetic component with superior caloric performance for low-profile high-density power conversion," Industry Applications, IEEE Transactions on , vol.40, no.5pp. 1287- 1293, Sept.-Oct. 2004

Abstract
This paper describes a magnetic component structure that features both low profile and the ability to achieve very high power and energy densities. A key characteristic which enables reaching both of these objectives is the incorporation of a foil winding with a high packing density and a unique shape factor, which enhances thermal and electromagnetic performances simultaneously. Although implementation of foil windings is common practice in magnetic component design, vertically wound foils to achieve low profile is not. Three prototype inductors are compared to a conventional litz-wound E-core inductor. Power dissipation and temperatures are measured in several different experimental procedures. At 140 kHz a power density of 1.8 kVA/in/sup 3/ was achieved for a measured efficiency of 99.5% and a steady-state hot spot temperature rise above the ambient of only 55/spl deg/C.

--C J Cowie 01:29, 11 January 2006 (UTC)

I have no doubt that Litz wire is used in high frequency transformers. What I doubt is whether it is used in mains frequency transmission and distribution transformers that User:Wtshymanski is referring to.--Light current 02:01, 11 January 2006 (UTC)

Not Litz wire, but stranded wire. See your own talk page. --Wtshymanski 02:03, 11 January 2006 (UTC)

If you dont mind, Im replying to my friend CJ Cowie here.--Light current 02:05, 11 January 2006 (UTC)

Do you have a reference saying that stranded wire is never used in power transformers? You seem rather definite on this for someone who's never been to a power transformer plant. See for example
  • Donald G. Fink and H. Wayne Beaty, Standard Handbook for Electrical Engineers, Eleventh Edition,McGraw-Hill, New York, 1978, ISBN 007020974X
Also mentioned in passing several places in my copy of the Federal Pioneer "BAT" newsletters, but unluckily they're at the office and I'm at home. --Wtshymanski 02:17, 11 January 2006 (UTC)
Multiple-stranded, individually-insulated conductors are used on the LV windings of large (300 MVA+) power-frequency transformers. See, for example, Central Electricity Generating Board (1982). Modern Power Station Practice. Pergamon. ISBN 0-08-016436-6. , p349. This book contains a diagram of the conductor layout, showing the subconductor transposition necessary to equalise the emfs in each strip. I have never encountered the term 'Litz wire' in this context, though. (In large transformers 'wire' is not really used as a conductor term). The main reason for employing transposed multiple strip windings in large transformers is not really a skin effect consideration, but rather to: (a) reduce eddy current losses in the windings themselves and (b) increase flexibility and aid the winding process. In a large generator, the same arrangement is known as a Roebel bar assembly, but I am unaware of the same usage being applied in the power transformer arena. --BillC 02:33, 11 January 2006 (UTC)

If you can quote a ref that Litz or stranded wire is used in transformers for the puposes of reducing skin effect, I will be very happy to see that fact included in the article. Its just tht I've never heard of it before and its not mentioned in any of my books on power transformers. It may be true but I think we need refs.--Light current 02:35, 11 January 2006 (UTC)

Now Bill, I think you have provided good info here and I suggest that this is added to the article forthwith. It will save much confusion.--Light current 02:38, 11 January 2006 (UTC)

Stranded wire references

http://www.nexans.ca/docs/contrans.pdf - A manufacturer of continuously transposed cable

http://www.wiretec.de/epctcprd_continuously_transposed_conductor.htm A manufacturer of continuously transposed cable

https://www.kuhlman.com/clientdata/PowerTransformersWebCatalog.pdf - "...low voltage windings are generally multi-strand, disk or helical type."

http://grouper.ieee.org/groups/transformers/info/F05/F05-CorrosiveSulfurPresentation.pdf - Page 69 shows strands

http://www.northerntransformer.com/pages/products.htm Multi-strand windings, continuously transposed cable

http://www.freepatentsonline.com/6087583.html - A new wrinkle on multi-strand conductors

http://www.eere.energy.gov/buildings/appliance_standards/commercial/pdfs/dist_trans_chp_3.pdf Transposition of multi-strand conductors to reduce losses (page 34)

Current edits

Gentlemen, this constant warring is not really working to the betterment of the article. If I can provide any assistance in resolving things, please let me know. --BillC 09:52, 12 January 2006 (UTC)

THis isnt war. THis is gentle sparring!--Light current 10:26, 12 January 2006 (UTC)