what is wrong here?

here load is a wye connection resistive load...

You are saying "the line currents is equal to both phases currents of the open delta". Is the load single phase? What exactly do you mean by "the load power is not equal to the supply power" ? Are you referring to amps or watts? How are you measuring these units?

no no, an open delta (just two phases) supplies a wye connected resistive load, all the phase phase voltages are 480 volt, line currents are 173 A.An open delta is supposed to have three equal line currents so line currents are 173A, but when you calculate the supply power 2x 480 x173 =166 Kw and load power, 1,73x 480x173 =144 Kw , so this is just a theoretical fact, can we conclude that the phase currents is not equal to the line currents for a open delta xformers??

Is the primary voltage on the transformer, whose second windings go from "delta" to "open delta," kept

1. the same level in both instances ("delta" and "open delta")?

2. balanced (the same level across all three phases) in both instances?

The situation depicted on the drawing with V-s and Amp-s is unrealistic. "Delta" "opening" like on the drawing should lead to dramatical voltage disbalance. Instead of 480V 480V 480V there would be 277V 277V 554V - I believe.

Yuri,

Very good!

Jon

Hi kuduk,

It appears one or two of the last of jinxnao posts have been wiped?

I have it listed but when I tried to read it the post was not there. End of story?

Interesting!!!

Jon

Baby,

You calls it as you sees it.

Kuduk

An open delta installations provides 3 phase. If you look at your drawing you will see 3.

I mean source phase, of course it has 3 phase but only 2 phase will supply power...

I cant understand, how such a paradox might be? the supply power supplied by open delta is bigger than balanced resistive load so how?? anyone can explain this dilemma ?

Do you mean open delta (where all the three phases will supply) or the scott connection (2 phase to 3 phase?)

Now in this sketch, the load what ever way you put star or delta, the input 3 phase currents are covered as output 3 phhse currents, there are no 2 phases here - unless you are using the neutral (then it is no more open delta connection) the phasor relation will not match, and it will be just a bit complicated center tapped transformer with heavy unbalances on either side.

I gave a link there(imageshack.us),and although the sketch seems reasonable powers are not equal u see too?? i wonder why?

THİS is exactly open delta, if you look at the imageshack photo u will see,I have examined all the sources on the net but i couldnt explain how can be an load unbalance between open delta and wye connected load in this picture, it is not sensible if u calculate too the loads, they dont agree, anyone there what i wanna say?

Guest,

The Scott-T configuration answer seems to be the logical one since it works both ways.

Most of my experience was using them to go from in and out of phase with variable amplitude to produce 3 phase outputs for Synchros.

Jon

it appears to me that you are quoting the current in two phases of the source, and the three phase load is getting the third phase from the neutral. The source is supplying the third phase through the neutral and I suspect the source is getting warm in the process. The power (less IR losses) is the same in both ends, you were neglecting the third phase power.

Hi jinxnao,

Are you sure the equipment is not transposing 3 phase to 2 phase? This seems very odd.

Does your system work or are you testing it because it does not work or is not reliable?

you all examined the scheme i sent??? i mean imageshack.us link..

so there is a illogical situation if u look from the point of powers, but as a source load relation the case seems logical, i cant differ them....

Hi jinxnoa,

Sorry to be pushy, but is the system you have working, or have you meassured it or tested it to see how 'good' it it?

open delta is when you still got 3 windings, not just two, but two of them are not connected.

Your image does not represent an open delta

http://books.google.com.tr/books?id=yFeM93ryHe0C&pg=PA41&lpg=PA41&dq=open+delta+system&source=bl&ots=WJjqzd34iU&sig=bwEu4rTj6f0c4hikSPSNOtSJg1A&hl=tr&ei=uLr2StPgBYK64Qbo3L3iAw&sa=X&oi=book_result&ct=result&resnum=10&ved=0CEUQ6AEwCQ#v=onepage&q=open%20delta%20system&f=false

hey look at here, it explains detailed but the situation seems weird to me, the second open delta scheme is a paradox for me, can u explain it from the point of powers ...

Jinx,

Your link says:

Which means:

Restricted Page

You have reached your viewing limit for this book (why?).

You have to buy the book. Jon

Hi jinxnoa,

I went to your second link and it makes sense as described.

If the phases are as say unbalanced and do not add up to what you expect they should, are you getting a line leak to earth or ground?

Is there another piece of equipment attached that you may have forgot or perhaps even do not know about? If in the the last instance, double check for other connections which are drawing power from one of two phases.

Do you need normal single (domestic) and three phase as the example you give on your last link suggests?

thank u for u care but i think i cant make understand what i mean, there is no an exceptional case considered at that book, it just says with an open delta connection u can feed the same load if u increase ur load 1,73 times, but as u see the power supplied is not equal to the power consumed...

Hi jinxnoa,

I went to another site and list the site and the definition of 'open delta', which may help.

http://www.toolingu.com/definition-460320-34157-open-delta.html

What is the definition of open delta?

• A transformer connection that does not complete the triangle, using only two of the three sides. An open delta is used when full power is not needed.
• Learn more about open delta in the class "Distribution Systems 320" below

Good luck

Jinx,

Considering that a Δ configuration can operate satisfactorily missing one winding, some power system designers choose to create a three-phase transformer bank with only two transformers, representing a Δ-Δ configuration with a missing winding in both the primary and secondary sides:

This configuration is called "V" or "Open-Δ." Of course, each of the two transformers have to be oversized to handle the same amount of power as three in a standard Δ configuration, but the overall size, weight, and cost advantages are often worth it. Bear in mind, however, that with one winding set missing from the Δ shape, this system no longer provides the fault tolerance of a normal Δ-Δ system. If one of the two transformers were to fail, the load voltage and current would definitely be affected.

So what IS wrong.

Jon

On the diagram phase A and phase C are short circuited.

Thanks Yuri,

That goes to show that people who create stuff for posting on serious websites need to have their material reviewed by others.

Jon

Here is an unshorted one:

okey i think no one knows what i ask, what u explain is all practical things, what I ask is this;

we have a 100 Kva THREE transformer, in delta we connect and feed a 3 phase wye connected resistive load, now if one of the transformers is gone in any way, so to be able to feed the same load we need to have not "150 KVA " but 173 Kva transformers (two piece ) , this means a %15,5 overload....

now here what i ASK İS this:
why two 150 kVA is not enough ??? if we need to connect two 173 KVA transformer in open delta, so what about the 46 kva EXCESS load?? why there is an excess ???

Jinxnao,

Because each of the two transformers have to be oversized to handle the same amount of power as three in a standard Δ configuration.

You may notice that I mentioned this before.

Where is your schematic?

Jon

yes but i think u havent read the sample i gave, i ask you of the excess power, as u see there is a power in excess of what is needed by the load...

Jinxnao,

The load determines the real power drawn from the source. If you could measure the heat dissipation of the load you would have an accurate power figure to work with.

If there is more power drawn from the source than used by the load it is due to the characteristics of the transformers and and how they are used to compensate for the missing power of a third phase.

Jon

Hi kuduk,

Can you tell me whether ohms law applies here to Transformers producing power as well as to current drawn? Just to answer a question which I think should be yes! But am not sure.

With thanks

Hi Baby,

Ohms law applies to the resistive loads with no problem.

With the phases and reactive parts it becomes a little more complicated but it all comes out okay after the math wiz gets his hands on it.

Jon

BB: Transformers do not produce power. They are only devices (not machines) that change the current/ voltage.

The ohmic losses do take place in the transformer- and that is decided by the so called equivalent circuits - ie the transformers when put in the circuit is treated as an ideal transformer with a series impedance (ie R & L)

And more interesting (or complicated) is that if you look from primary side it is different from when you look from secondary side. (Like V & I the impedance also is transformed)

Hello Guest,

I appreciate your reply post to me, many thanks!

I would like to thank you for the 'ohmic' detail and bits on the workings of Transformers.

I am by no means an electrical wizard as it seems you are.

But, as a Transformer of the size mentioned is usually the receiver of the power from the Grid and or power plant, it does 'supply' or redirect it by means of windings, shunts etc. I should have made that more clear.

I was finding it hard yesterday to actually put down in an understandable way what I knew was happening, but that is my problem. I was trying to get over my meaning to the OP (Original Poster). If I was an Electrician I would have 'had it off pat', knowing the names of the internals and external parts and configurations of all and any power Transformer, but, as I am keen to point out, I am no electrician and was just trying to get over the principles of the workings of these 'two' 'for three' types of configuration of Transformers.

I thank you sincerely for your kind post.

The reason to oversize the 2 transformers is to make up for the missing phase.

Hi jixnao,

I think the previous post may have answered you but I will give you what I think you mean, even if I do get it wrong! LOL!

I may be coming at this from the wrong direction, but, hey whats new.

Having read details on a couple of sites, it seems although you have very little to fall back on if something goes badly, IE you may not have enough power. These Transformers are built using several basic sizes. grouped in threes or twos, but each in that group is the same size, so you can't have a 50KVA and a 100 KVA. they are either 70 Kva x 2, or 100 Kva x 2. Just for instance, OK.This is in the open delta mode.

There is a 2x 70 Kva and you have to supply 130 Kva which, means you have 10 Kva more than enough.

I may have it wrong but does ohms Law rule still apply, when producing power, and when using it? If so you have 140 Kva capability, so this gives you 10Kva over capacity. But if ohms law applies the current actually used will be the current which has to be produced?

Is this right or not?

Bear in mind that although you may have over capacity, you have bought only two parts of a potentially three part Transformer, so you are saving on that.

If someone can tell me if this is not true, please put me right.

I am not an electrician, so forgive me for possibly screwing this up.

Hi jinxnao, I could not have a look in your image attached, sine my firewall stops all the peer-peer sharing sites for obvious reasons.

However as I can understand you are getting confused by the magnetic flux balances.

Try to understand this way, The energy transfer in transformer is by the flux linkages. For same energy to transfer the flux density is to be maintained.

The 3 transformers are working - a flux of Φ is generated. Now one transformer is removed.

Assuming the load is same, it demands the same power and hence same flux. This flux linkage requirement now is to be met by the rest of the two phases.

Since they are connected and on 3 phase lines, the calculations will involve the sqrt(3) factor.

If you do the analysis on this line and try to visualise from this angle you will see what is happening.

hi guest, yes what u tell about is true but i think all the magic can be tucked into a few words nevertheles...

Seems to me that the quality of the questions has been getting lower and lower. One wonders why the figures don't add up.

There are 2 transformers doing the work of 3. Therefore the current/work produced through the 2 have to be equal to the 3 transformers they take the place of. That means the windings have to handle the increased current or they overheat and blow up.

The sum of the phase angle current drawn from the three transformer circuit should equal the phase current drawn from the two transformer circuit.

The only difference is the heat produced being greater for 2 transformers, hence the degrading of the ratings to overcome the extra heat produced.

And this kind of question and harrasment from a commentator.

ı think you think that all the thing is so easy that you can say only "there occurs an overload in the windings cooz there are now only two winding instead of three.."

i think it is not so simple, yes it is very obvious that there will be an overload but i want that everybody does see the real situation here, as i said before ;
there is three 100 kva xformer, feeding a 300 kva load, now one of the windings is gone and now the power which one of the two winding should supply is not 150 but 173 kva, so i ask you all the engineers here till i get a satisfactory answer,,, WHY???

Hi jinxnao,

I refer you to post 17. Please answer this.

Thank you

Hi Guest,

Are you the sender of post 42? And if so was your last line which mentioned harassment aimed at me from my request for you to join (Because you sound like a clever bloke) in post #41.?

The problem with me trying to answer a 'Guest' is, unless you are following the thread carefully it may not be obvious as to which person or 'guest' I am replying to.

I am not saying sorry because I was very careful in sending you that post and thanking you for your help with the 'ohmic' query, and asking you to join.

If you wish to complain to the management of the site about my post please do so. Here is the person to whom you should send your complaint:

And you will get an answer if you join.

Or you can just click the Report button and just say in a few words what you are complaining about, OK?

42 Re: what is wrong here? 11/10/2009 3:21 AM

Seems to me that the quality of the questions has been getting lower and lower. One wonders why the figures don't add up. There are 2 transformers doing the work of 3. Therefore the current/work produced through the 2 have to be equal to the 3 transformers they take the place of. That means the windings have to handle the increased current or they overheat and blow up. The sum of the phase angle current drawn from the three transformer circuit should equal the phase current drawn from the two transformer circuit. The only difference is the heat produced being greater for 2 transformers, hence the degrading of the ratings to overcome the extra heat produced. And this kind of question and harassment from a commentator.

My comment was not aimed at the guru, but the commentator that started the question. The questions seem to me to be comming from students that need the assignment questions answered. After the question had been answered 4 or 5 times differently saying the same thing, I think one is dense of worse when they keep hounding others to explain it.

I have seen commentators put out a question (as a question) as to how something works and those are good learning even for me. That's why I read this blog almost every day although I read every forem for articals.

Please accept my appoligy, but harrasment was not aimed at you, but the commentator that would not let well enough alone about the oversized transformer. I am not an electrician, but know some that have stated "national code" dictates that the transformer will be oversized by a certain amount. I would have remembered 1.5 times but if 1.73 is the factor, then so be it. It's a fact, national code, accepted practice that has been tried and true for years.

No, I was not 42.

Signed guest Karl Mavis

Hi Guest,

I just wondered whether you mean quality of questions, or quality of replies?

by the way, i am an electrical engineer , and some of u think that i ask annoying questions since they think that they do say true whenever they speak but i see that they do err; i will explain why later....

Hi jinxnao,

I am pleased you posted to explain you are an Electrical Engineer, thank you!

But I have to say, as far as I can see there has been no one trying to put you down or insulting you. I realise you did not say this but I am trying to guess what the part of the post you left off was going to say.

Good luck.

Hi jinxnao

I have just reread your OP (Original Post) shown in bold below.

What is the supply power and where is this power coming from? Is it the 'GRID' or your own generator?

Please read and check you have not missed out a word in your OP.

I may be stating the obvious, and I am sorry for that but, you have the

power supply in--->>>---Transformer--->>>---power supply out to sockets.

Would you find it easier perhaps to follow these simple steps and list the current or supplied power for each? This is only a suggestion, OK?

This is not intended to be any kind of insult, OK.

a open delta supply is supposed to supply a 173 A 480 volt resistive load, the line currents is equal to both phases currents of the open delta, but here the load power is not equal to the supply power . So what is wrong here??

hello friends, i think i repeated my question so many times that it reached a perfection grudgingly:)

i think this is very difficult to explain ( i am sure that u can explain if u can understand) such a simple question to understand :(i dont claim that the answer is so easy to understand in first looking..)

There is a delta- wye transformer of which primary consists of three 100 kva single phase and this supplies a three phase wye pure resistive load ok?? is there a question? nooo ?? okey lets go on...

now if one of the phases (here single phase transformers) is (burnt gone whatever u say) now these two one will go on supplying the same load okey? is there a problem?

no?? lets go on again:)

now on the contrary of the simple urging of our intuitions ; one of these two phases will not get loaded 150 kva per phase but 173 kva okey? is there any objection?

is there real engineers who care about my question?? if u can stop talking about some funny and needless theories which have nothing to do my question as form and contents i plead you to focus on these simple datas so as to answer my question simply in the same manner, any way dear Engineers;

now the simple question is this ; why an excess power of 23 kva is absorbed ???

i have repeated this question so many times that this is the last one, i think u dont focus on the question enough! otherwise i am sure u will make the answer slip instantly lol....

Hi jinxnao,

Just a few words to congratulate you on your comic jokey writing.

At first I really thought you were joking from the start. I wonder if you are still joking, as you seem to say near the end of your post that you actually do understand what is happening. I just wonder what your motives are now. I for one do not think this is a game. And I think if you do know the answer to your own request, then you should tell us so others who may be looking for that answer.

Good luck.

Do you remember there was a similar thread some 6-7 months back from cnpower ? this thread is also gooin on same line - it was something to do with geometry- I don't remember - but it has moved along exactly same lines, and the end answer was not very interesting.

BTW: Cnpower also is not visible- or he is like me? let us wait if he is, he is going to explode over this

also it is a big ill-luck for us to be not able to see the link afterwards, there explains many in detailed way, if u cant answer still , i will make an explanation simply, i just want to see what u will say, if it is still not obvious for u i will ignore all the written here and forget about it...

Jinx,

If you knew trhe answer why did you ask?

Jon

i did not knew, but i think i know now and i will explain after your answers...

i am still so amazed about the amount of the turmoil which this op have created...

Jinx,

It seems that some folks think CR4 Electrical Engineering is more fun with the added turmoil.

Jon

note: i name the secondary of a three phase transformer, which is connected delta in first case and ofterwards its one phase is gone as supply and the three phase wye resistance block as load ,as u can see from the imageshack.us link, i had thought the image was explanatory enough...

Jinx,

The open delta transformer configuration has big power losses when it supplies a load intended for the missing aid of a 3rd phase.

Jon

no this is not the answer, i am waiting still someone to answer correctly........

Jinx,

You may notice that I am just throwing stuff out to keep the thread alive while we all wait for the climactic answer.

Did you like the drawing where the transformers had shorts across the supply lines? Talk about excess power draw! Pow!! Only one person mentioned it.

And what's with the Turkish website you put in one of your posts with a page that doesn't open? That was funny! Like you were trying to sell that guy's book so folks could read the restricted page you were directing them to. There are better books.

I can't wait to see what you come up with next.

Jon

first of all the web site i have given was not a turkish website but it was google books portal, i think u did not read the link even superficially dear guru:)

secondly what i mean with excess power should be clear to u if u are guru really but u dont seem to be so till now! excess power is also seen on the first link i gave, i think u can at least see through this drawing and find me right in just a 30 second, just P = 1.73xI.V not so difficult u must try a bit...

and finally dear guru, i think to be able to find an answer to problems here is not so simple what a pity, if u want to learn the real answer u should search at least 100 book if necessary, if u cant let me know and i will tell u the secret of all...

(it is really amazing that i couldnt get the answer since 10 days and u are trying to make fun of me still, i think u should give up waiting for my next bombs and instead try to focus on the question...)

also dear guru this link works here, if it doesnt condescend to work there in your country i cant do anything...

Jin,

If you leave "tr" out of the address it would have worked here too. You could have responded to the reported problem and tried to fix it for the people who you wish to entertain.

It is still Turkish Google but the page does open for viewing.

The page does explain what I have alluded to previously but why would I want to spoil it for the rest by revealing your secret.

Kuduk

Jinx,

"first of all the web site i have given was not a turkish website but it was google books portal, i think u did not read the link even superficially dear guru:)"

I clicked on your big long http: link and copied the webpage you offered from Google and put it in here <http : / / books . google . com. tr> is certainly a Turkish language Google Books portal.

"secondly what i mean with excess power should be clear to u"

"Excess power" is the nature of the broken third phase called configuration called open delta.

if u are guru really but u dont seem to be so till now!

Guru simply means I have gone beyond 500 entries in CR4. I don't think it has much meaning beyond that.

(WARNING: If your implication is intended to insult it is a violation of the terms of service on CR4.)

"excess power is also seen on the first link i gave, i think u can at least see through this drawing and find me right in just a 30 second, just P = 1.73xI.V not so difficult u must try a bit..."

You mathematics works good in the DC world but not in the ac and multiphase transformer invironment. That is what is wrong.

"and finally dear guru, i think to be able to find an answer to problems here is not so simple what a pity, if u want to learn the real answer u should search at least 100 book if necessary, if u cant let me know and i will tell u the secret of all...

Ah yes, key words: Want and can't. Asumptions.

"The Secret". Sounds like a good title for another Dan Brown fiction novel.

(it is really amazing that i couldnt get the answer since 10 days and u are trying to make fun of me still, i think u should give up waiting for my next bombs and instead try to focus on the question...)

Most of the more serious minds had already looked over your stuff and passed on it without making a comment here. Most of them don't like stuff that looks like it is from a homework assignment.

Jon

dear guru!

if u think that the extension tr is enough for a google books portal to be a turkish site so i trust in u, and i must thank google managers for feeling themselves as turks, i love them all..

excess power is not supposed to be the match for the extra load taken charge of by the two transformers from the missing transformer but the 23 kva (from my example)which has no match with regard to the load part, i think u havent understood still what i mean lol...

i think guru means in reality much more than ur definition...

in my example and question the load side is pure resistive and u dont need cos phi so i think u should evaluate the cases more meticiliously....

yes assumptions since i cant talk about realities and magnificience regarding u....

yes i think more of them thought that they had 100 books to read to be able to give an decent answer to my question and give up in advance , but what makes me amazed is that u still go on wrong way...

NOTE : İ DONT MEAN İNSULT ANYONE, İf u felt so i am sorry...

Jin,

Google is cool. Make you feel at home wherever you are.

Sometimes it is just a cultural thing that makes people seem like they insult. No worry.

Excess power is what the two remaining transformers must be able to handle to make up for the missing third transformer to satisfy the load. That's a lot of heat for those remaining two.

Guru is not MY definition. It is what happens to you in CR4 when they exceed 500 posts. It is a title related to participation.

Participant, Active contributer, Associate, Commentator, Power User, Guru etc. You may notice that Baby has 4031 posts and 70 good answers and is a Guru. Another person has more than 10000 posts and 210 good aswers and is a Guru. Another person has almost 600 posts and no good answers and is a Guru. Nothing much to do with the good answers or smarts.

Kuduk

Baby,

You speak from my heart.

Kuduk

Hi kuduk,

You say I speak from your heart!........... I like it!!!

I also speak from mine and one or two other as well me thinks?

That explains Load VA not equal to Supply VA but the question still remains

Why "load power is not equal to the supply power ."

of course banter! so i think hence this affair is done, i thank all my friends for trying to help me, see u in the other threads...

Tee Hee Hee! all that made for an entertaining thread. Stuff like this adds the appropriate amount of 'intellectual' sparring to keep it fun as well, thanks all.