The T.M.Haja Sahib Transformer efficiency thread

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Besoeker

Senior Member
Location
UK
If you want to say that installing a transformer with 65% extra capacity to save energy as TH seems to be suggesting I disagree with that.
It's a good point and one that most of us here, myself included, have not addressed.
It's total losses that matter rather than efficiency.
 

mivey

Senior Member
THIS is the problem TM could not see past: it is NOT 2% difference in efficiency! It is 2% when losses are compared to the transformers full rated kva, but NOT the the actual efficiency at lower loads! At lower loads the efficicency seldom changes by even 0.2%!
Neither my links nor the link you provided seem to support that. I'm pretty sure they were discussing out/in percentages. Perhaps I should run the calcs but I thought the graphs spoke for themselves. Even in your link, compare the efficiencies listed in the TP-1 tables (for example 50 kVA 150C at 100% load vs a 100 kVA 150C at 50% load: 97% vs 98.4% = a 1.4% difference).

What TM insists on is comparing a transformer losses to its rating, NOT to the load attached. So Yes, comparing the lower losses at 50% load to the xfmrs full load rating IS maybe 2% less, but not when you compare power out/(power in +losses). Therein was TM's shortsightedness.
Why would you ratio power out to power in + losses? I thought power out / power in is what we were chasing. Am I not thinking clearly or what? I am between meetings but I did not think I was that distracted.
 

mivey

Senior Member
A case of remembering wrong.
The research into the original "TP-1" justification found a 24hr average loading of 35%.
Was not referring to any research, just the TP-1 publication. What was researched and what is required may or may not be the same. Bes was thinking the 35% requirement was an average, but it is a set point. The manufacturing requirement is based on the NEMA TP-1 set point of 35% (or 50% for some transformers), not an average. A 35% set point like you said.
The current version of TP-1, is a specific point of 35%.
Yeah, that's what I said.
 

mivey

Senior Member
My read on your post was that you had come to save the day,.... set us all straight with some new info ..... etc. and I saw nothing new in your post.

From your link it showed very little difference between 35% and 100% loading.
There was dispute with one of T.M.'s statement. One response was that the transformer was most efficient at 100% load. Not so.

Another was that it was just a small insignificant fraction of a percent difference. 1-2%, on the scale of transformer efficiencies, is a big difference from 0.2-0.3% efficiency. But not enough to justify putting in a transformer that is 3X too big.

Maybe the difference comes from knowing where TM started.

A thread was opened and someone had asked how much they could load with a transformer Charlie B had suggested 100% was OK.

TM said no, you must have spare capacity
Which is silly, of course.

When no one bought into that he changed to claiming there would be a savings by installing a transformer that was too large.
As Bes pointed out, the savings would not offset the capacity costs.

So if you want to say a specific transformer may be more efficient by a small margin at 35% loading I have no issue with that.
Good. Then we can cancel the HBO special.

If you want to say that installing a transformer with 65% extra capacity to save energy as TH seems to be suggesting I disagree with that.
I have already said that makes no sense.
 

mike_kilroy

Senior Member
Location
United States
Neither my links nor the link you provided seem to support that. I'm pretty sure they were discussing out/in percentages. Perhaps I should run the calcs but I thought the graphs spoke for themselves. Even in your link, compare the efficiencies listed in the TP-1 tables (for example 50 kVA 150C at 100% load vs a 100 kVA 150C at 50% load: 97% vs 98.4% = a 1.4% difference).


Why would you ratio power out to power in + losses? I thought power out / power in is what we were chasing. Am I not thinking clearly or what? I am between meetings but I did not think I was that distracted.

Your first paragraph is comparing apples and oranges; we were never comparing 2 different size xfmrs with different designs; the comparison is on ONE individual transformer at full load and a lower load. Comparing a volkswagen to a corvette offers no insight. so please look across a SINGLE row of the efficiency charts to see how ONE design varies with different loads: you will not find a single one that shows 1% or even anywhere near that efficiency change.

Your second paragraph again shows TMs efficiency comparison mistake: he is comparing as you suggest here (power rating/power in+losses) which is as meaningless as an accountant proving that $ 2.00 is really $14.00. Efficiency is out/in not comparison to some arbitrary setpoint such as transformer kva rating. guess you got me on semantics here tho.. of course pwr out/pwr in is what we are comparing - so I SHOULD have said power out/ power out +losses.. sorry but thought everyone would understand the point.
 
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mivey

Senior Member
Your first paragraph is comparing apples and oranges; we were never comparing 2 different size xfmrs with different designs; the comparison is on ONE individual transformer at full load and a lower load. Comparing a volkswagen to a corvette offers no insight.
Since the load is fixed at the installation time, isn't comparing two different transformers kind of the whole point?

so please look across a SINGLE row of the efficiency charts to see how ONE design varies with different loads: you will not find a single one that shows 1% or even anywhere near that efficiency change.
:? Not that one transformer is the issue, but how about the 50 kVA one I mentioned? It has a 1.2% drop from 25% to 100% loading.

Your second paragraph again shows TMs efficiency comparison mistake: he is comparing as you suggest here (power rating/power in+losses) which is as meaningless as an accountant proving that $ 2.00 is really $14.00. Efficiency is out/in not comparison to some arbitrary setpoint such as transformer kva rating.
OK, I now see that you were talking about T.M.'s formula. I'm not sure the point he was making, but it was obviously not clear. Perhaps T.M. will chime in and clarify.
 

mike_kilroy

Senior Member
Location
United States
1) Since the load is fixed at the installation time, isn't comparing two different transformers kind of the whole point?

2) Not that one transformer is the issue, but how about the 50 kVA one I mentioned? It has a 1.2% drop from 25% to 100% loading.

1) The OP had a specific question: Should I load my transformer to 100 or less? Nothing to do with multiple transformers or buying a second transformer. The thread did go on to encompass specs and whether to oversize or not, and how much to oversize a new transformer, but in each case my understanding was it was clear ONE transformer was being discussed.

2) Again it was my understanding this was about a large 3 phase xfmr, not a single phase aluminum one like you pointed to. If you want to find a really bad apple, pick the 167kva in the same first chart you looked at: 68% eff @ 25% & 98% at 100%.... There will always be wierd ones, and single phase xfmrs will often exhibit worse efficiency numbers from no load to full load. If you go down the charts and pick 3ph alum you will see more typical is:

50kva 914D 531 270 1316 eff: 97.7 98.1 97.9 97.5

Anyway, I think what this thread has shown, at least to me, contrary to statements from TM, is:

1) Oversizing a transformer will generally cause more watts loss for a given load (since the larger transformer will have higher core losses) so will inherently be less efficient,
2) The small (ok call it upto 1.5%) typical efficiency change from say 1/2 load to full load on a transformer is basically insignificant to use as a design point,
3) Transformers can be designed for extra high efficiency and also for reasonable ratio of core vs i2r losses
4) Per the Eaton efficiency chart sited, trading core losses for i2r losses has little bearing on efficiency at different loads as would appear to 'make sense' - there are just too many intertwined design relationships to it.
5) When designing a new system requiring a transformer, it makes sense to provide more capacity for future growth and the amount of extra is a personal engineering decision at this point and not a required amount by code.
 
T

T.M.Haja Sahib

Guest
Oversizing a transformer will generally cause more watts loss for a given load (since the larger transformer will have higher core losses) so will inherently be less efficient,

From the same Eaton charts,it may be seen that higher size transformer has slightly higher efficiency and if so chosen not only to make the given load fall within its maximum efficiency range i.e to consume less energy but also to meet the near future load demands,the choice of higher size transformer is the best option.
 

mivey

Senior Member
1) The OP had a specific question: Should I load my transformer to 100 or less? Nothing to do with multiple transformers or buying a second transformer. The thread did go on to encompass specs and whether to oversize or not, and how much to oversize a new transformer, but in each case my understanding was it was clear ONE transformer was being discussed.
Since the load is a given, you have a choice of serving it with a transformer loaded at 100% or serving with a larger transformer loaded at less than 100%. It is pretty clear we are chosing between a fully loaded vs a partially loaded transformer. That decision process requires looking at more than one transformer.

2) Again it was my understanding this was about a large 3 phase xfmr, not a single phase aluminum one like you pointed to. If you want to find a really bad apple, pick the 167kva in the same first chart you looked at: 68% eff @ 25% & 98% at 100%....
Obviously the 68% was a typo that was supposed to be 98%.

There will always be wierd ones, and single phase xfmrs will often exhibit worse efficiency numbers from no load to full load. If you go down the charts and pick 3ph alum you will see more typical is:
Then instead of the 50 kVA single phase, use the 3-phase 150 kVA and you drop 1.3% efficiency from 25% to 100% loading.

These numbers are consistent with the two graphs from the two links I provided. The point was that the efficiency percent change was not limited to practically no difference across the range. Also, it shows that efficiency does not continue to rise with loading. In those respects, T.M. had a point.

Where T.M. did not have a point, and I think we all agree, was that extra capacity was required and that the change in efficiency over the loading range made it economical to put in a grossly over-sized transformer.

T.M. seems to be missing the difference in efficiency percent vs. NPV for a given load.
 
T

T.M.Haja Sahib

Guest
S
Where T.M. did not have a point, and I think we all agree, was that extra capacity was required and that the change in efficiency over the loading range made it economical to put in a grossly over-sized transformer. T.M. seems to be missing the difference in efficiency percent vs. NPV for a given load.

Higher sized transformer is different from over sized transformer.The former can be an economical engineering choice,while the latter may be an uneconomical layman's choice.Of which are you talking about?
 

ActionDave

Chief Moderator
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Licensed Electrician
Higher sized transformer is different from over sized transformer.The former can be an economical engineering choice,while the latter may be an uneconomical layman's choice.Of which are you talking about?
That distinction can only be made once you define what is meant by above in relation to over and higher and the transformer. Until then over and higher mean the same and all further discussion is muddled. When you can see the sky where is the ceiling?
 
T

T.M.Haja Sahib

Guest
That distinction can only be made once you define what is meant by above in relation to over and higher and the transformer. Until then over and higher mean the same and all further discussion is muddled. When you can see the sky where is the ceiling?
Distinction is made on the basis of choice by an Engineering Professional.
 
T

T.M.Haja Sahib

Guest
The requirement is mandated by modern electrical design;by the bitter experiences of modernisation works.
 

Besoeker

Senior Member
Location
UK
Argument for argument's sake?
Not at all. It is pertinent to the choice of transformer.
If I bid for a project, the overwhelming probability is that I will be in competition. Possibly with competitors and/or other projects for funding.
If I price for larger than required transformer ratings for the application the chances are that Joe Bloggs or John Doe, will be able to undercut my offer and maybe win the business that we could otherwise have had.
I could possibly make a technical and commercial case for improved efficiency reducing operating costs - if there was one. But, as I and others have pointed out, efficiency differences over the likely operating range are generally pretty small so that just might be a bit of a hard sell.

Another aspect of this on larger projects like, for example, a water pumping station is that the initial purchase comes out of a capital budget and running costs come out of an operations budget. Sometimes this can result in different priorities. Projects want a short term gain which might give operations some long term pain.

There's no "one size fits all" approach.
 
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