The T.M.Haja Sahib Transformer efficiency thread

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T.M.Haja Sahib

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How are we to know how much spare capacity to be prepared for? Would we then need to increase capacity when we use up the spare capacity so there is more spare capacity again? What if we have 600 amp service - with 200 amps of spare capacity, then owner decides to put on addition that requires 800 amps of capacity for the addition alone? What good did that extra 200 on the original installation do for us?
Keep those questions ready to ask the code panel after it has eventually made the spare capacity for an electrical system a requirement.(now it is only a recommendation.See Sec 90-1B) :D
 

iceworm

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Keep those questions ready to ask the code panel after it has eventually made the spare capacity for an electrical system a requirement.(now it is only a recommendation.See Sec 90-1B) :D
If the code panel for art 90 ever gets that stupid and I happen to run into a member, I would never ask them, "Why?". Why would one ever ask "Why?"? What reason could they give that would possibly matter? And I really don't see the point in asking questions where the answers don't matter.

Just exactually how would you expect an AHJ to interpret, "reasonable provisions for system changes"? This is a retorical question - because they can't. The interpretation is subjective. There are no criteria. The AHJ imposed requirements would be all over the map.

Art 90.1.A,B,C are pretty well written. The NEC is absolutely clear that it is for "practical safeguarding of persons and property", "essentially free from hazard", and "not intended as a design specification". It does not require a 100% safe, reliable, upgradeable, system - because no one wants to pay for 100%.

Yes - It is about the money.

You are certainly welcome to a different opinion. And, I'm absolutely okay with your opinion being considered as valid as mine. I do recomend that when you give your opinion, you back it up with examples from personal experience, references, and reasoned logic. Opinion given as statements without these is useless.

ice
 

don_resqcapt19

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Keep those questions ready to ask the code panel after it has eventually made the spare capacity for an electrical system a requirement.(now it is only a recommendation.See Sec 90-1B) :D
If they do, it won't last long. It will be removed by the courts as an "illegal taking" of private property (money) without due process. Of course for that to happen some one would have to take the issue to court. There are a number of other code rules that would probably not withstand a court challenge. Most are not worth the cost of a court case, but with large facilities it could be.
In addition, the requirement for oversized transformers would not be a "green" thing. It would waste energy and raw materials.
 
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iceworm

Curmudgeon still using printed IEEE Color Books
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EE (Field - as little design as possible)
Keep those questions ready to ask the code panel after it has eventually made the spare capacity for an electrical system a requirement.(now it is only a recommendation.See Sec 90-1B) :D

If they do, it won't last long. It will be removed by the courts as an "illegal taking" of private property (money) without due process. ...

Don -
I didn't know that happens. I have heard of court challenges on code interpretation - where the AJH is way out of line with their version. But I had not heard of what sounds like you are describing as a Constitutional challange. I have heard of this type of court action where the city or state wants someone's property to build a mall. I didn't know it applied to a state law passed NEC. I thought the usual was for individual states to pass the code with exceptions.

Disclaimer: On these types of issues, I am completely out of any areas of my expertise.

ice
 

bob

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The :dunce::dunce::dunce: is appropriate for some situations IMHO.

quote = eric9822]The :dunce::dunce: is appropriate for some situations IMHO.
Agreed.:)


That may be true but I would hope that both of you would not feel the need to use it.








 

don_resqcapt19

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Don -
I didn't know that happens. I have heard of court challenges on code interpretation - where the AJH is way out of line with their version. But I had not heard of what sounds like you are describing as a Constitutional challange. I have heard of this type of court action where the city or state wants someone's property to build a mall. I didn't know it applied to a state law passed NEC. I thought the usual was for individual states to pass the code with exceptions.

Disclaimer: On these types of issues, I am completely out of any areas of my expertise.

ice
I think there is a strong basis for a Constitutional challange of codes. The only issue is the cost to mount such a challage would far exceed the cost of complying with the code rule. I think anytime there is a code rule that goes beyond the protection of public safety, that required compliance with the rule is an illegal taking of property without due process. I am not aware of any such challange, but maybe there should be some. We far too often let the government trample on our rights without objection.
 
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T.M.Haja Sahib

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Just exactually how would you expect an AHJ to interpret, "reasonable provisions for system changes"?

The intent is to see whether any engineering judgement is exercised to include any future load demands in the design of an electrical system.

Art 90.1.A,B,C are pretty well written. The NEC is absolutely clear that it is for "practical safeguarding of persons and property", "essentially free from hazard", and "not intended as a design specification". It does not require a 100% safe, reliable, upgradeable, system - because no one wants to pay for 100%.

But its recommendation for spare capacity is really obscure and so you seem not to see it.

I do recomend that when you give your opinion, you back it up with examples from personal experience, references, and reasoned logic.
Well,I thought my statements were convincing enough and logical enough.But if you think they were just my opinions,you are not correct.
 
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T.M.Haja Sahib

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.... the requirement for oversized transformers would not be a "green" thing. It would waste energy and raw materials.
No,it is not,for the maximum efficiency of a distribution transformer does not occur at 100% loading but far below.
 

eric9822

Senior Member
Location
Camarillo, CA
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Electrical and Instrumentation Tech
It is still a design issue and not a safety issue which the NEC is intended to address. Transformer efficiency is affected by losses and an oversized transformer will waste energy. A good design will allow for growth but if I want to install a transformer loaded at 100% or 10% I should be allowed to as long as it is safe and complies with the current code.
 
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kwired

Electron manager
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The intent is to see whether any engineering judgement is exercised to include any future load demands in the design of an electrical system.



But its recommendation for spare capacity is really obscure and so you seem not to see it.


Well,I thought my statements were convincing enough and logical enough.But if you think they were just my opinions,you are not correct.

But how do we define what the possible future load will be?

Lets say we build a manufacturing plant, we size equipment for known load. Then we see that we are currently running process A and shipping it somewhere else to do process B. If there is a goal to one day move process B to the new plant you have an idea of what kind of future load you may have - but that is totally a design issue. If totally new but associated product C comes along and needs its own production line and space we may not have had any idea it would even happen or what kind of capacity would be needed when the original plant was built.

Maybe we should install 2000 amp services in single family dwellings just in case. I'm all for it because I would make more profit on materials:thumbsup:
 
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T.M.Haja Sahib

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I am afraid you are mistaken because providing for spare capacity is an essential element of modern design and it is beneficial to incorporate it in the code as a requirement so that that essential element of modern design is not missed by the designers!.But this is not the place to continue our discussion further as it would be construed as OT.
 

iwire

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Massachusetts
I am afraid you are mistaken because providing for spare capacity is an essential element of modern design and it is beneficial to incorporate it in the code as a requirement so that that essential element of modern design is not missed by the designers!.But this is not the place to continue our discussion further as it would be construed as OT.

You should put in a code proposal expressing your concerns and your solution.

Anyone can submit code proposals.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
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EE (Field - as little design as possible)
... Well,I thought my statements were convincing enough and logical enough.But if you think they were just my opinions,you are not correct.
Yes, that is what I think- mostly opinion. Here is an example.

No,it is not,for the maximum efficiency of a distribution transformer does not occur at 100% loading but far below.
Do you have any peer reviewed documentation that this statement is true? I'm not saying it is not true - I don't know either way.

If you don't have any documentation then this statement is just an opinion.

ice
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
No,it is not,for the maximum efficiency of a distribution transformer does not occur at 100% loading but far below.

TM -
I am interested in any documented testing you know about showing transformer efficiency as a function of loading. I don't recall seeing any tests or papers on the subject. I'm sure they are available, I just have not seen them.

It doesn't have to be peer reviewed lab testing. If you did the testing, or have solid information from who ever did the testing, that would be fine.

However, if the only information you have is that someone told you that they know of testing showing the xfm efficiency was greater at low loading than at 100% load - then that is useless.

ice
 

Besoeker

Senior Member
Location
UK
TM -
I am interested in any documented testing you know about showing transformer efficiency as a function of loading. I don't recall seeing any tests or papers on the subject. I'm sure they are available, I just have not seen them.

It doesn't have to be peer reviewed lab testing. If you did the testing, or have solid information from who ever did the testing, that would be fine.

However, if the only information you have is that someone told you that they know of testing showing the xfm efficiency was greater at low loading than at 100% load - then that is useless.


ice
Transformer efficiencies are generally quite high so the better efficiency argument proffered by our friend is a bit of a red herring.
But, FWIW, I have some data on a 400kVA transformer that we used on a project.
Losses referred to full load rating are:

1/2 load, 0.75% losses
3/4 load, 1.00% losses
1/1 load, 1.75% losses

Suppose that, instead of running my 400kVA at rated load, I uprated it to 800kVA to run at half load.
The transformer efficiency would change from 98.3% to 98.5%.
That difference would take an awfully long time to recouple the difference in price and to save the additional energy used to produce the bigger transformer in the first place.
 

mike_kilroy

Senior Member
Location
United States
xfrm efficiency

xfrm efficiency

No,it is not,for the maximum efficiency of a distribution transformer does not occur at 100% loading but far below.

First I am not allowed to let my customer use the full rating of the transformer we design for him (only 80%?), but now he shouldn't because its max efficiency point is "far below" max rating....

I sure wish my engineering teachers in college taught me this 30 years ago so I could have oversold every transformer I ever did! I would be 20% richer today!

One of our last designs:

Our 400 kva transformer watts loss:
core loss: 3960.7
coil loss 4636.9
total loss: 8597.6



hmmmm.... ok now some math..... core losses are there irregardless of load, so
constant. the coil losses are I^2R losses..... so efficiency based on load:


480v, .020ohm, so 481.7amps

0 load: 3960.7 = 1.00%
1/2 load: 3960.7+1160.2= 1.28%
3/4 load: 3960.7+2610.4= 1.64%
full load: 8597.6/400000= 2.15%

By gosh the efficiency IS a lot less at lower loads. But someone PLEASE tell me what significance this has to the use of a transformer? By this reckoning, we should use ALL transformers at their most "efficient" point: 0% load!
 
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