Spin Turn 1

[karalahana]

Hello, I wonder if there is a relation between the power of a transformer and turn number of its spins? if so how can be determined the turn number of a xformer of any power ?

 

[davidbeach]

Spin? Never heard that term regarding transformers.

 

[wareagle]

Maybe he is referring to the transformer turns ratio.

 

[davidbeach]

That was an initial thought, but reference to "turn number of its spins?" kind of eliminated that. Besides there is absolutely no relationship between power rating and turns ratio, so I doubt that turns ratio was the question.

 

[waross]

spins, windings, as in
"Number of turns in a winding."?
I think that the answer is
"No." The number of turns affects the voltage but not the power rating. The power is more related to the amount of iron in the core and the size of the openings for the windings. There is not a direct relationship, but the weight of a transformer compared to a similar transformer will tell you more about the capacity than will the number of turns.
This is a very rough approximation, as in a heavy motor may have more power than a lighter motor.
It depends.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[karalahana]

hello, I mean the number of turns of both sides, excuse me spin was wrong termAny way so I wonder what determines the number of turns , with what this number changes. I mean not " ratio "but "NUMBERS of turn".
Also what do u mean with"the size of the openings for windings "? ,?t is strange to me what is "opening" here and what a relationship with the power?

 

[davidbeach]

I'll throw this out and then let the transformer guys take over. The determination of the number of turns is part art, part science, part economics, and part black magic.

Pick a conductor size for the necessay ampacity at the hotspot. Do this for all windings.

Start adding turns to both sides until you are at the required turns ratio and you have the required impedance.

That doesn't close? Increase the conductor size on one side (or both) and try again.

The big boys probably feed everything into a computer program and get their starting point from that.

 

[rbulsara]

Start with a good book on Electric AC Machine Design.

Rafiq Bulsara

http://www.srengineersct.com

 

[MAGTiger]

There is not a simple relationship but rather a process of transformer design. If the transformer is a few hundered kva or smaller, the relationship will be strongly influenced by the given manufacturer's "standard" frame sizes. These would be predesigned structural members used to hold the assembly together. And the tooling used to wind (spin) the coils. Larger transformers are less likely to have standard predesigned components to draw from. We do use the area product to get a general sense of core size and help select a core frame. Area Product = the product of the core window area times the coil window area in inches to the 4th power. We would tabulate our standard frames based on this number to get a relative core size against KVA.

Standard frame sizes may get redesigned every several years as economical choices change the ratio of copper or aluminum to silicon steel cost.

The size may be determined by desired impedance, losses, dimensional constraints and economics of materials. Without a standard core frame to start from the variability of cores sizes is practically infinite. Generally speaking, more turns of wire and less core cross section means higher impedance more copper loss (load related loss) and less core loss (constant loss). If the customer evaluates losses then it becomes even more complicated actually assigning a $ value to core watts and a different value to coil losses.

Neil

 

[karalahana]

so just tell me this please, if we apply the minimum possible ratio so as not to increase the load losses is there any advantage we lose as we limit the turn number? .I mean if we double the minimum turn numbers of a transformer is there any benefit we can get from this not regarding the load loss due to the length of the copper at primary and secondary? Excuse me rbulsara but I think even good introduction books dont cite the solution of this question,And I am not able to understand the design books since I dont manufacture xformers...Magtiger you are very kind thank you...

 

[waross]

The ratio really doesn't have much to do with the losses or the power. To explain losses would take several chapters in the book that you don't want to read.
As the primary voltage is increased, the flux density in the core increases. At some voltage the core will saturate and the primary winding will probably burn up. A couple more chapters will explain saturation.
The primary voltage should be kept below the saturation point.
If the number of turns on the primary winding is doubled, the allowable voltage will be doubled.
Ratio: Pretty simple, the primary voltage divided by the secondary voltage. eg. primary voltage 480V, secondary voltage 120V, the ratio is 4:1.



Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[karalahana]

excuse me but I think I couldnt make clear what I asked,I ask if there is a good result of having greater number of turns of windins of a transformer if we omit the copper losses of windings ? ?s it conventional that you apply to a transformer the mimimum suitable numbers which gives the ratio or can this be multiplied due to some necessities? I am trying to get what determines the numbers of turns .Thank you that you tried to explain many useful things but what I am asking is just a simple question to reply....

 

[waross]

Saturation determines the maximum voltage per turn. The rated voltage divided by the maximum voltage per turn gives the number of turns needed. More turns is wasteful.
Get a book. Read a book.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[karalahana]

oh this is the gist ... thank you...

 

[electricpete]

Yes, that is a good overview.

Volts per turn = V/N = d/dt (Phi) = 2*pi*f*B*A
We can see from this that another important variable in determining number of turns is core cross sectional area A. For given frequency f, voltage V and target flux density B, you could get away with fewer turns N by making the core area A larger....but then every turn is longer to reach around the larger core (a tradeoff).

=====================================
(2B)+(2B)' ?