The T.M.Haja Sahib Transformer efficiency thread

[mike_kilroy]

to follow up on this, what DOES happen if you use a double size xfmr to make it "more efficient?" If one adds the actual WATTS losses, they will see this more efficient xfmr actually is LESS efficient at 1/2 load would he not? 1.28% of 800kva= 10,240watts loss........ 2.15% above is 8597.6watts loss on the 400kva transformer for the same load? Which is "MORE" efficient?

efficiency is power in/ power out so just to state a transformers different load points by itself is silly.

 

[mike_kilroy]

thinking about this, I just had to write one more idea: TM proved by his point that under utilizing a transformer actually is LESS EFFICIENT than not. If you use 100% of a transformer, you do not oversize it and thus you do not add more core losses that then make the overall watts loss for a given load more.

 

[kwired]

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.

I don't think it is OT. OP kind of hinted at this very issue. It is still not a code issue it is a design issue. If it were put into code how much extra capacity should be designed into any particular installation? There is no single answer that fits all installations, and even similar installations would not always end up with the same future possibilities.

 

[T.M.Haja Sahib]

I don't think it is OT. OP kind of hinted at this very issue. It is still not a code issue it is a design issue. If it were put into code how much extra capacity should be designed into any particular installation? There is no single answer that fits all installations, and even similar installations would not always end up with the same future possibilities.

Thanks,kwired,for your hint.Let us first see how the code recommends spare capacity despite in an obscure way in sec 90-1B.

 

[kwired]

Thanks,kwired,for your hint.Let us first see how the code recommends spare capacity despite in an obscure way in sec 90-1B.

And the very next section says "This Code is not intended as a design specification or an instruction manual".

You just said it "the code recommends spare capacity". It does not "require" spare capacity. There is no way they can mandate any specific amount of spare capacity, as there is no way to know what future needs will be that fits every application.

 

[T.M.Haja Sahib]

TM -

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

You mean you do not believe this also?
http://forums.mikeholt.com/showthread.php?t=142122&page=2

 

[T.M.Haja Sahib]

And the very next section says "This Code is not intended as a design specification or an instruction manual".

Yes.But it does not matter.The code is not design manual,rather it is a 'warning' manual.

There is no way they can mandate any specific amount of spare capacity, as there is no way to know what future needs will be that fits every application.

It is not necessary to mandate any specific amount of spare capacity,but just to require that provision for spare capacity is made in the design.The intent is to bring into the awareness of an electrical designer that spare capacity is an essential element of modern electrical design and it shall not be missed in the design.

 

[kwired]

Yes.But it does not matter.The code is not design manual,rather it is a 'warning' manual.



It is not necessary to mandate any specific amount of spare capacity,but just to require that provision for spare capacity is made in the design.The intent is to bring into the awareness of an electrical designer that spare capacity is an essential element of modern electrical design and it shall not be missed in the design.

So if I allow just 10 VA of extra capacity I should be fine, or I could allow 1,000,000,000,000 extra VA either way works they are both additional capacity.

 

[T.M.Haja Sahib]

So if I allow just 10 VA of extra capacity I should be fine, or I could allow 1,000,000,000,000 extra VA either way works they are both additional capacity.

Yes.You,the electrical designer,also a professional is free to decide on the basis of future demand the spare capacity required in the design.

 

[kwired]

Yes.You,the electrical designer,also a professional is free to decide on the basis of future demand the spare capacity required in the design.

You are the one suggesting that there should be or some day will be a requirement for spare capacity. Just how do you see that being something that will work? There has to be more to it than just requiring extra capacity otherwise I could do just like I previously mentioned, calculate my total VA and add 10 more VA and I have some extra, or 100, or 1,000,000 .... Then you will also have the issue of what to do when you finally do use that extra capacity? Now you have no extra capacity. Would that be a violation to leave it with no extra capacity?

 

[John120/240]

TM Haja Sahib, Say that we design with spare capacity. Then you add more loads. Now we

have used that spare capacity. So what will we do......add more spare capacity when we add

new loads ? It's a dog chasing his tail an exercise in fulitity.

 

[topgone]

TM Haja Sahib, Say that we design with spare capacity. Then you add more loads. Now we

have used that spare capacity. So what will we do......add more spare capacity when we add

new loads ? It's a dog chasing his tail an exercise in fulitity.

Makes me laugh a lot! Might as well drive a nail in our heads if you follow his line of thought.

The amount of spare capacity depends on how deep the pockets of the owner is. It is not because it is specified in the codes. We will design for safety and operability, period. Extra margin is desirable but those come with extra costs.

Digging deeper, if you are told in advance that the load growth is Z %, you need to compute for the necessary Y dollars for a y capacity and compare with X dollars for an x future capacity that will be needed in that W years in the future. Bluntly, sizing entails expressing all pros and cons in dollars and basically how convincing the designer is to the owner/s. We get paid by satisfying the needs and wants of the owners.

 

[T.M.Haja Sahib]

TM Haja Sahib, Say that we design with spare capacity. Then you add more loads. Now we

have used that spare capacity. So what will we do......add more spare capacity when we add

new loads ? It's a dog chasing his tail an exercise in fulitity.

I think if you had done any modernisation works,you could have easily seen how badly things were designed without taking into account any spare capacty that might be required in future......

 

[T.M.Haja Sahib]

You are the one suggesting that there should be or some day will be a requirement for spare capacity. Just how do you see that being something that will work? There has to be more to it than just requiring extra capacity otherwise I could do just like I previously mentioned, calculate my total VA and add 10 more VA and I have some extra, or 100, or 1,000,000 ....

Assiging a spare capacity to cater to future demands is no easy matter.It requires discussion with the owner of the building etc.,

Then you will also have the issue of what to do when you finally do use that extra capacity? Now you have no extra capacity. Would that be a violation to leave it with no extra capacity?

Every equipment has a finite economic life......

 

[iwire]

Interesting how TM chose to ignore the posts that actually show the calculations demonstrating how oversized transformers use more energy for a given load.

 

[T.M.Haja Sahib]

Thanks,iwire.I did not read those posts.

 

[Besoeker]

efficiency is power in/ power out.

Vice versa otherwise you'd get efficiencies of >100%

 

[T.M.Haja Sahib]

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.

On the contrary suppose your load requirements would grow from present design load of 400 KVA to beyond but within 800 KVA in near future,would you buy 400 KVA transformer or 800 KVA transformer?

 

[Besoeker]

I think if you had done any modernisation works,you could have easily seen how badly things were designed without taking into account any spare capacty that might be required in future......

That's not about bad design. It's 'cos someone picked the wrong crystal ball that day.

 

[T.M.Haja Sahib]

That's not about bad design.

It is.Spare capacity is a concept of modern electrical design.