Talk:Transformer/Archive 5

message: I don't have a lot to say about the question of flux/no-flux; I think the answer depends on how you define things and where you measure. I will suggest, however, that you forget the idea of "the core" versus "the air". The core is just a means to concentrate the magnetic flux and thereby increase the inductance, but short of core saturation and to a first approximation, there's no difference, in principle, between the way an iron core transformer and an air core transformer operates.
Atlant 18:25, 18 May 2006 (UTC)
replies: text: There is a magnetic flux in the core, and there's nothing subjective about it.  There's a clear explanation on allaboutcircuits.com.  I'll summarise it thus.  The voltage across the primary creates a flux in the core.  This flux depends only on the primary voltage, regardless of what the secondary is doing.  Why?  Because Ep=dΦ/dt, and Ep has constant amplitude; therefore, Φ, which is common to both windings, must have constant amplitude.  If a load is connected to the secondary so that a current flows in it, then there is an invisible tug-of-war between the two windings.  The secondary tries to induce an infinitesimal bit of extra flux, which is immediately and exactly counterbalanced by an infinitesimal increase in flux in the opposite direction from the primary, so the net flux stays constant.  --Heron 19:32, 18 May 2006 (UTC)
replies: text: Well Atlant, I tend to agree with some of your above statement, but wherever you measure in the core, you will still find only the magnetising flux regardless of load current. I was trying to point out the need for flux cancellation in a loaded transformer. Highly permeable cores do, of course, concentrate the flux and increase pri inductance as well as increase coupling between windings.--Light current 22:58, 18 May 2006 (UTC)
replies: text: Yes Heron, I'm talking about when there is a secondary loading, in which case sec. current flows and the fluxes are cancelled. This is the normal operation of a transformer. Otherwise I agree with the last part of your post except that its the pri current (H =IN, B=uH, phi=BA) that creates flux in the core. Also, I submit the  the net flux you quote is merely the magnetising flux - nothing more.--Light current 22:58, 18 May 2006 (UTC)
thread_title:  Others' comments 

message: As part of our ongoing discussion, Light current asks:
:What IS a transformer? Curioser and curioser. 9-))
Blame it all on the magnetic monopole. Seriously, while we understand all of this EM stuff at a sufficient level to design and use technology based on electromagnetism, when you really get down to thinking about it, magnetism itself is still magic, a complete mystery to physicists. So if we start asking the really deep questions, the state of the art simply isn't advanced enough to provide answers. ;-)
Atlant 15:48, 19 May 2006 (UTC)
replies: text: I hate not knowing how transformers work, so I've been searching the web for several days to get some more information on this question.  Nearly every website repeats the same formula about MMFs summing to zero, and none of them explains how the energy gets from one side to the other.  Then I Googled up these two posts -  and  - on sci.physics.research from 1999.  They mention an entity that we haven't considered yet: the leakage flux.  According to those posts, this is what transfers the energy.  The magnetizing flux is a red herring.  Atlant, I take your point about the ultimate inscrutability of magnetism, but perhaps it's not magic after all! --Heron 20:38, 21 May 2006 (UTC)
thread_title:  Blame it all on... 

message: This resultant flux in the core must (only) be the magnetising flux. In a core of inf. permeability, no mmf is required to magnetise the core. Although the magnetising flux in a real transformer induces voltages in both the primary and sec, in itself it does not (cannot?) carry any energy from pri to sec. That this is so can be deduced, for example, from the fact that the mag current/flux will remain constant with sec load. 
A small difference between pri and sec MMFs is the result of the non zero reluctance of the practical (non ideal) core. This difference in MMFs is given by the product of the flux density and the reluctance.(cf V=IR)
Energy is transported by the cross product of the E and H fields only (Poynting vector) and flux in the core is only a by product of the primary H field having to be guided to the secondary winding by the core.
I think this explanation answers all previous objections. (athough I could be wrong - again!). 
Is everyone (inc WTS) happy with this exposition/explanation? Please respond as I may like to put the 'essence' of this explanation in the article. (maybe replacing some of the current explanation)--Light current 20:03, 4 June 2006 (UTC)
thread_title:  Summary of transformer operation 

message: I think the diagram needs to be altered to show two opposing fluxes: one due to pri AT nd other due to sec AT. Any comments?--Light current 13:52, 19 May 2006 (UTC)
replies: text: No, I disagree. It would make it horribly messy. You've argued for this before. --BillC 16:55, 19 May 2006 (UTC)

text: The new reference should be added of course, and well done to Heron for researching it. I note that the Edwards and Saha paper shows a transformer diagram that is identical (bar the reversed secondary winding sense and concomitant reversed secondary current) to the transformer diagram here. Is our diagram still wrong? --BillC 17:43, 22 May 2006 (UTC)
thread_title:  Diagram 

message: When Omegatron said:
When we split it into smaller articles, can we please divide them in a sane, logical way?  We need to decide on the talk page what to split it into first, and then, when a consensus is reached, start doing the splitting.   (I am, of course, thinking of Capacitor, Capacitor (component), and Capacitance when I say this...) —
Did he mean that the capacitor thing was not done right? --Light current 17:59, 30 August 2006 (UTC)
replies: text: Yes. — Omegatron 03:43, 28 November 2006 (UTC)
thread_title:  Page splitting 

message: Hi Light current.  I know that I've moved the "analogy" section before, but please don't think that I'm persecuting you.  I had to move it because your last edit resulted in a non sequitur, with the analogy immediately followed by the second half of the overview, but no "end of analogy" warning.  Evidently our opinions differ on where to put the analogy, but I won't revert your next move as long as the article remains consistent. --Heron 09:19, 27 May 2006 (UTC)
replies: text: Yeah I thought the analogy was better in the overview rather than in the nitty gritty details of the electrical explanation.. I will take more care to make things follow properly before moving it again. 8-)--Light current 16:50, 27 May 2006 (UTC)

text: Thank you (I think!)--Light current 19:27, 4 June 2006 (UTC)
thread_title:  An analogy 

message: I hadnt realised that Atlant! so good edit. Yes, rectifiers are usually a nuisance to the power companies! 8-)--Light current 17:43, 1 June 2006 (UTC)
thread_title:  Half wave recs and dc in sec. 

message: Im rather reluctant to suggest this and do not want to cause any hysterics, but does anyone think that one or both of the diagrams below should be incorporated into the page? 8-))--Light current 02:25, 3 June 2006 (UTC)
replies: text: This article doesn't need to replicate the hysteresis article. Add too much explanation and you'll find that to understand transformers is to understand the sum total of human thought to date. Wikipedia articles should *focus* and not ramble on every possible relationship between the putative subject and the rest of the known universe. --Wtshymanski 18:44, 3 June 2006 (UTC)
thread_title:  Hysteresis and reluctance 

message: I agree.  The article is way too long as it is.  Focus!  Pfalstad 06:01, 6 June 2006 (UTC)
replies: text: Ok suggest how to split it. 8-|--Light current 14:00, 6 June 2006 (UTC)
thread_title:  Page split? 

message: The "alternative analysis" still troubles me and I think it is in fact wrong. As I've always seen it described, the primary and secondary MMFs don't cancel in the mathematical sense.  The primary MMF is negligably small assuming a very large permeability of the core, but it is *required* in order to sustain flux in the core.  You must have flux else there's nothing to change and so voltage across the winding. Secondary current produces an opposing MMF, so primary current must increast to provide the ampere-turns required to sustain the flux.  It all comes of trying to divide by zero.  It would be better to think of the "ideal" transformer as being the limiting case as permeability heads toward "infinity", which is a term that always causes trouble in an engineering context. --Wtshymanski 18:31, 10 June 2006 (UTC)
replies: text: The alternative analysis is incorrect.  For the ideal transformer, the permeability of the core is infinite.  When this is the case, H cannot exist in the core for if it did, B would be be infinite.  Without any H in the core, the mmf of the primary and the secondary must exactly cancel.  However, and this is where the alternative analysis section get its wrong, zero mmf does not imply zero flux.  In the ideal core, flux exists without mmf.  Interestingly, the 'other' characteristic of an ideal transformer - zero leakage flux - is unaffected by the ideal core.  To achieve zero leakage flux would require surrounding the core and windings with material that has zero permeability.  Alfred Centauri 19:55, 10 June 2006 (UTC)
replies: text: Let us therefore change the wording in accordance with the sentiments of the above 2 posts!--Light current 01:12, 11 June 2006 (UTC)

text: Aha! Is that the hidden message in Alfreds earlier exposition: that transformes can only work if they are in a medium with non zero premeability>? This seems obvious now but wasnt before!--Light current 01:20, 11 June 2006 (UTC)
thread_title: Still irked

message: What is the basis of selection of Vector Group while making the selection of Transformers?
: That's a very general question. If you want two transformers to operate in parallel, you must have the same relationship in phases between primary and secondary terminals. If you wish to create a neutral for a distribution system, you must choose a transformer with a winding that has a star point. If you're dealing with multiple DC rectifiers, you may alternate vector groups in order to create less harmonic distortion on the primary system. ( And you can sign your posts with --~~~~) --Wtshymanski 17:39, 21 June 2006 (UTC)
replies: text: That's no longer an "artificial neutral" since it will allow zero sequence currents to flow. Where it's desirable to provide a grounded neutral for a system without sourcing zero-sequence current, you will find a zig-zag transformer ( guess no-one's written that article yet) to provide a neutral without letting fault currents flow phase-to-ground. --Wtshymanski 17:57, 22 June 2006 (UTC)
thread_title:  Transformer vector group 

message: Caption says its a step down. But it could equally well be a step up. Can we remove the qualifier 'step down' from the caption?--Light current 18:04, 30 August 2006 (UTC)
replies: text: How could it possibly be a step up?  You can count the number of turns as well as I can.  — Omegatron 03:53, 28 November 2006 (UTC)
replies: text: You could turn it round! I think at one time the primary and sec were not labelled and so it could have been either. But as shown now, it is a step down device. 8-)--Light current 03:55, 28 November 2006 (UTC)
replies: text:  Primary and secondary have always been labeled.  You can look through the various revisions yourself, just as you can look through the revisions of an article.  Here's how it looked in January 2006, for instance. — Omegatron 04:42, 28 November 2006 (UTC)
replies: text: And of course it depends on how you define the words 'primary' and 'secondary'. In fact many transformers are commonly used backwards! 8-)--Light current 04:53, 28 November 2006 (UTC)
thread_title:  'The' diagram 

message: its very interesting to get article on why transformer doesnt tend to rotate?
its principle and theory is expected.
:You tell us why you think it should rotate, and we'll tell you why you're wrong. Your answer is expected. --Heron 10:05, 3 September 2006 (UTC)
thread_title:  analogy of transformer with motor 

message: From the article: Audio frequency transformers, (at the time called repeating coils), were used by the earliest experimenters in the development of the telephone. 
:I originally edited this line because the phrase "at the time" or "then" comes before any reference to when or at what time. It sounds confusing because the reader can't be sure if the time is during the developement of the telephone or some other time before that that was established in an earlier sentence.
:After that was reverted I followed the repeating coil link and found that the term still seems to be used.  That seemed to me to make the "then" clause unnecessary so I removed it.  That got reverted.
:I don't understand what was wrong with my edits or what is so special about the original phrasing.  -Crunchy Numbers 16:54, 8 September 2006 (UTC)
thread_title:  [[repeating coil]]s 

message: Light Current, you should have reverted that last one by 63.23.18.109. They broke some links and added added a little how to with old transformers. I was in the process and got called away before I saved and then you edited something.
-Crunchy Numbers 23:52, 22 September 2006 (UTC)
replies: text: Sorry didnt spot it! 8-( You are welcome to revert back over my changes!--Light current 00:10, 23 September 2006 (UTC)
thread_title:  Edit by 63.23.18.109 

message: You know, if I picked up a printed encyclopedia that told me after a turgid explanation "this may seem contradictory", I'd fling it with great rapidity through the nearest window. Can we please get an explanation of how a transformer works WITHOUT using phrases like this (which are a clue to the encyclopedia reader that the writer(s) haven't a clue what they are talking about)? --Wtshymanski 21:50, 10 October 2006 (UTC)
replies: text: Agree! I was waiting for someone else to change it. Maybe you could oblige? 8-)--Light current 22:11, 10 October 2006 (UTC)

text: And cite some references. — Omegatron 21:51, 25 November 2006 (UTC)
thread_title: Encyclopedic writing

message: I have tried to clarify the DC behaviour of transformers. The previous section was incorrect, particularly in its assertion that a DC voltage does not induce a changing flux. All voltages are changing fluxes!
I hope it's reasonably clear for non-technical readers (my intention). The gist of the section is that DC voltages are very very very bad news, and DC currents are not so bad at low levels but still are not the show-stopper that DC voltages are.
::Eh? Could you translate? And sign your posts using ~~~~--Light current 03:52, 28 November 2006 (UTC)
thread_title:  DC Behaviour Clarifications 

message: Since when did Wikipedia talk pages become discussion forums where the laws of physics were decided by consensus?  Get some references!  I'm skeptical of this "no flux in a transformer" business, and the "DC transformer" aspect of things is poorly explained.  
However, using a transformer with DC voltages would require the magnetic flux in the core (and current supplied by the DC voltage source) to increase without bound.
That makes no sense.  An ideal transformer transfers energy without loss.  If a 1:1 DC transformer has a voltage source connected to one side and a resistor connected to the other, it will behave exactly as if the transformer weren't there.  The power transferred from the source to the load will be constant, the voltage will be constant, the current will be constant.  If the current increased without bound, you'd be sourcing more and more power over time, but the power dissipated in the load would stay constant.  Makes no sense.
Also, the whole point of the ideal transformer is to act as a building block in constructing models of real transformers.  I don't even see this mentioned.
I've found a bunch of references for DC transformers to list, at least:
* "The ever-elusive ideal transformer would perform this function over an infinitely wide frequency range (including DC) and with zero loss.  Even though such an element is physically unrealizable, it is nonetheless a useful starting point for constructing models of real transformers" - The Design of CMOS Radio-Frequency Integrated Circuits   
* "It would be useful at this stage to introduce the concept of the ideal DC-to-DC transformer (a transformer that would provide a DC output for a DC input). Although this may seem a strange concept at first, consider the conventional ideal transformer model. The ideal transformer would pass all frequencies from DC upward in both directions, with no power loss. It would provide any required voltage or current ratio, and would have infinite galvanic isolation between input and output. It would also provide the same performance for all windings. Clearly such an ideal device does not exist." - Switchmode Power Supply Handbook  
* "The ideal transformer transforms direct voltage, i.e., DC voltages on primary and secondary sides are related by turns ratio.  This is not a surprising result because for the ideal transformer, we have assumed infinite core material permeability with linear (non-saturating) characteristics permitting core flux to rise without limit under a DC voltage application." - Transformer Engineering: Design and Practice  
* "For ac voltages and currents, an ideal transformer gives results that are within a few percent of those of the corresponding actual power transformer.  But for dc voltages and currents, an ideal transformer gives incorrect results.  The reason is that an ideal transformer will transform dc voltages and currents while an actual transformer will not." - Schaum's Outline of Theory and Problems of Basic Circuit Analysis 
* "Ideal Transformer: The ideal transformer is a lossless transformer. It differs from the perfect transformer as it will pass DC and all frequencies. It is of course unrealizable in the 'real world'; however it serves as a building block for building complex, non-ideal transformers." Magnetics (Part 1) - Transformer Modeling
* "It is a fact of life that the physical device called the “transformer” cannot operate properly in a dc circuit. The ideal transformer, because it is ideal, is defined to work according to equation (2) equally well for dc or ac voltages and currents, or any combination of the two." The Ideal Transformer
* "However, the diminishing impedance value of these inductors as the frequency is lowered implies that there’s a lower frequency bound to which this will work. As a consequence, the coupled-inductor model doesn’t simulate an ideal transformer at zero hertz (dc)." A Spice Model For The Ideal Transformer
Also, I've discovered that you can create a real-life "DC-DC transformer", though not capable of transmitting any power, and, I think, working on a different principle from regular transformers.  Apparently superconducting sheets are placed near each other and the DC voltage is created on the other side of the gap by flux vortexes or some other phenomenon that's over my head.  Search for "Ivar Giaever". — Omegatron 04:35, 28 November 2006 (UTC)
thread_title:  References 

message: Hallo!
>Perhaps you can tell me, or on the article's talk page, why you're >adding these hand-drawn pictures. What are they adding to the >article?
Many European readers don't use, understand the USA-symbols!
Today is my first day on Wikipedia. So I'm still learning the Wikipedia way of doing.
Greetings,
Martin Segers
martin.segers@scarlet.be
www.hasselt.be
www.judoveldwezelt.be/handen/segers/a.html
Tsi43318 14:18, 3 February 2007 (UTC)
replies: text: But what symbols? Your new diagrams have Vp, Vs and ф, all of which are in the coloured diagram above. — BillC talk 15:03, 3 February 2007 (UTC)
thread_title: New diagrams

message: Yes, I probably was a bit over the top. A simple one liner would have more than sufficed. Probably better to take out the warning. However, in industry this type of warning is taken seriousely, CTs are never open circuited when on load. A typical example is where one ammeter is switched between 3 CTs measuring a 3-phase circuit. The 3-way switch used is of a special design. The two un-connected CTs are always shorted out by the switch contacts, moving the switch position first shorts out the CT being measured before the next CT is connected using a make before break design The requirements in industry are probably more stringent due to higher voltage & energy levels. 
In an ordinary trafo, the supply voltage is assumed to remain constant, & the value of the primary current is determined by the load current; but in a CT, the load current flows through the primary winding, & the term voltages of the 2 windings are practically proportional to the primary current. 
If the CT secondary is opened on load all the primary ampere-turns are then available to produce flux, The iron loss due to the high flux density could result in excessive heating of core & windings & dangerousely high e.m.f. in secondary. Shorting the secondary will not result in excessive current, as this is proportional to primary current which is determined by the load & not the secondary current. Suckindiesel 21:10, 21 February 2007 (UTC)
thread_title:  == The new "WARNING!" ==