208v to 240v Buck Boost Transformer Calculations

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iwire

Moderator
Staff member
Location
Massachusetts
I hate to enter a battle of wits as I am unarmed, but is this not covered by 450.4 ?

:)

I posted it already.

But OCP is not really the topic I was talking about. I was very specifically talking about the kVA load on the auto transformer itself. Not the kVA load on the OCP nor the kVA drawn by the load.
 

mivey

Senior Member
mivey: Cool, Cool. This is just a disscusion.
It is an exercise in you not admitting you were wrong. Its that simple.

By the way you did not comment on example 3.2 of my last post, which shows how to calculate AT apparent power from 2 winding isolation Tr . Study it
Nothing to comment on as it has nothing that refutes Iwire's post.

As for the content, there is nothing new or revealing. I know how transformers work and so do many others here. If we were trying to teach others we could go into more detail.

But you are just beating a dead horse to make it sound like you were right and Iwire was wrong.

You were wrong. Get over it and move on.
 

Sahib

Senior Member
Location
India
The mistake is taking size of 2 winding Tr as that of the AT. The example 3.2 clearly shows it. Dont you see it?!
 

mivey

Senior Member
The mistake is taking size of 2 winding Tr as that of the AT.
That is not what Iwire said.

Build as many strawmen as you want but it won't change the fact that you were wrong. I know it. Iwire knows it. Others here know it. If you really don't know it by now there is not much else to add.
 

Sahib

Senior Member
Location
India
who is wrong here? See post 37. iwire stated load on AUTO TRANSMER LESS THAN 1:5KVA.
 
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winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
With all due respect winnie, the only thing Sahib is trying to do is to twist what Iwire said about the load on the transformer into something about the size load it can manage.

The rest is distraction to cover his original mistake.

I agree with your observation of what Sahib is doing, but I think he has a different basis for his misunderstanding.

As I see it, he is unwilling to admit to his part in a language misunderstanding, rather than trying to correct it. Rather than try to figure out why we are not communicating, Sahib is telling us that we don't understand the physics of transformers.

I believe that he is counting as part of the transformer the wires leading from the supply and the wires leading to the load... and counting power delivered directly from the source to the load as part of the transformer rating. In his language, if the transformer as configured is delivering 15kVA, then it is a '15kVA autotransformer'.

All the rest of us are only counting the windings and core, and saying that any power directly delivered by the source to the load is _not_ part of the transformer rating.

Imagine I sell you a box called a 'voltage raising unit' (not specified to be a transformer). It is rated to go from 208V input to 240V output, with 47A rated output. It has 2 input terminals that you connect to a 208V supply, and it has 2 output terminals.

What would you call the VA rating of this 'voltage raising unit' box?

Now when you open the box you find that internally it has a 240V to 32V transformer connected in a voltage boost configuration. This _component_ of the voltage raising box has a 1.5kVA rating.

I will affirm that a _transformer_ consists of the coils and core, and that any loading on that transformer is from voltage applied across the coil terminals and current flowing through the coils. I do not count power going 'around' the transformer as part of the transformer rating.

-Jon
 

Ingenieur

Senior Member
Location
Earth
What you say and what he meant are all wrong. You both have confused the OP.

I don't know (care) if you are being stubborn or just don't 'get' it
but matters not, your understanding is incorrect
no big deal, you'll get over it
no use explaining it
it takes the same knowledge to generate the correct answer as it does to SEE it when others present it to you
 

Sahib

Senior Member
Location
India
I believe that he is counting as part of the transformer the wires leading from the supply and the wires leading to the load... and counting power delivered directly from the source to the load as part of the transformer rating. In his language, if the transformer as configured is delivering 15kVA, then it is a '15kVA autotransformer'.
All the rest of us are only counting the windings and core, and saying that any power directly delivered by the source to the load is _not_ part of the transformer rating.
Exactly. The example 3.2 of my earlier post#73 clearly shows how to calculate the KVA rating of the autotransformer from the 2 winding transformer which is in line with what I am trying to make you understand that inductive component of power transferred alone does not constitute the rating of the autotransformer.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Exactly. The example 3.2 of my earlier post#73 clearly shows how to calculate the KVA rating of the autotransformer from the 2 winding transformer which is in line with what I am trying to make you understand that inductive component of power transferred alone does not constitute the rating of the autotransformer.

Well you won't communicate that effectively by telling some very smart people that they don't understand how transformers work or laughing at them. Instead you should be agreeing on the physics and showing examples of where the _wording_ is used differently.

In the example you referenced, where a 10kVA transformer was used in a boost configuration, the example shows a 110kVA load being served, and we would all agree with this calculation.

However the document itself does _not_ say that the transformer has a 110kVA power rating. The exact words from the document are 'the apparent-power rating when connected as an autotransformer.'. Not 'power rating' but 'apparent-power rating'.

I bet that if you called the authors and asked, they would say that the transformer rating remains 10kVA, but that the ability of the transformer to serve a load is similar to that of a 110kVA isolation transformer, thus the use of the term 'apparent-power rating'.

-Jon
 

mivey

Senior Member
I bet that if you called the authors and asked, they would say that the transformer rating remains 10kVA, but that the ability of the transformer to serve a load is similar to that of a 110kVA isolation transformer, thus the use of the term 'apparent-power rating'.
Jon,

You will find both "apparent rating" and "rating" used by credible sources for the 110 kVA. You will not find them saying the actual load on the transformer is more than 10 kVA, which was Iwire's point.
 

Sahib

Senior Member
Location
India
You will not find them saying the actual load on the transformer is more than 10 kVA, which was Iwire's point.
WRONG wrong. Once an AT is formed, there is no separate isolation Tr in it. It transfers power both by induction and by conduction. iwire mistake is he thinks power tranfer by conduction is independent of AT. It is not.
 

kwired

Electron manager
Location
NE Nebraska
WRONG wrong. Once an AT is formed, there is no separate isolation Tr in it. It transfers power both by induction and by conduction. iwire mistake is he thinks power tranfer by conduction is independent of AT. It is not.
Transfer and transform are not the same thing. Net load is transferred through a portion of the transformer. Only a portion of the net load is transformed within the transformer with an autotransformer. An isolation transformer does transfer and transform 100% of the load.

The circuit conductors transfer the load as well.
 

mivey

Senior Member
iwire mistake is he thinks power tranfer by conduction is independent of AT. It is not.
Your mistake is thinking that is what Iwire said. Another strawman to add to your collection.

You should note what it means to transform energy.

I don't you want to or are able to understand Iwire's point.
 

mivey

Senior Member
Transfer and transform are not the same thing. Net load is transferred through a portion of the transformer. Only a portion of the net load is transformed within the transformer with an autotransformer. An isolation transformer does transfer and transform 100% of the load.

The circuit conductors transfer the load as well.
Post missed in passing but that is one thing Sahib doesn't appear to get or acknowledge.
 
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