Transformer Design-Turns ratio

[savvej]

Considering a practical transformer design,
We can get a given voltage and corresponding current ratio by selecting a particular turns ratio.
ie. V1/V2=N1/N2=i2/i1
Say that I want to make a 240V/60V.
Now 240/60 volts ratio can be acheived by considering different no. of turns on primary(P) and secondary(S).
like:
1)P=4 turns ,S=1 turn
2)P=24 turns,S=6 turns
3)P=120 turns ,S=30 turns
4)P=240 turns,S=60 turns
5)P=4800 turns S=1200 turns
So we have various options for a given voltage ratio.So will each of the above turns ratio work?
Then why do we have 230-60V / or 230-12V transformers so bulky.How does current rating affect no. of turns?

 

[crutschow]

There are other critical design requirements for transformers besides relative turns ratio, such as the inductance and core saturation.

You must have enough primary turns to create sufficient inductance at the operating frequency so that the magnetizing current with no load is sufficiently low (typically a few percent of the full load current).

There must also be sufficient windings so that the magnetic flux density does not saturate the core at the voltage peak of the input waveform. This is determined by the number of turns and the magnetic saturation value of the core material.

The current rating doesn't affect the number of turns. It just affects the size of the wire required to carry the current without overheating the transformer. This, in turn, affects the size of the core needed to accommodate the turns of wire.

Suggest you read up on transformers such as this article.

 

[awt]

In a simple language, the higher the power, the higher the current rating, the larger the core and fewer the turns. Frequence, core properties and so on, also have effect on it.

 

[savvej]

@crutshow thanks.
Crudely though,neglecting "You must have enough primary turns to create sufficient inductance at the operating frequency so that the magnetizing current with no load is sufficiently low (typically a few percent of the full load current). ",I have come up with this:
Consider a P=240 S=60 turn transformer.What I think is that if I wind such a transformer ,And if I check up Voltage at secondary,it should be indeed be 60V ,IF NO LOAD WILL BE CONNECTED.But if I connect a load(in normal case),due to the current set up ,opposing flux will be set up in the core and to maintain flux,current will be drawn from the primary.But what will happen in this case is,though all flux of primary is linked with secondary,not all flux of secondary will be linked with primary(if the no. of turns are sufficiently small) and hence,the transformer will not be able to deliver any current.
What is your say?

 

[crutschow]

If "all flux of primary is linked with secondary" then all flux of secondary is linked with primary. They are one and the same flux. So I don't understand your statement. The number of relative turns between primary and secondary has little to do with the flux linkage between windings. Obviously transformers work and deliver current.

 

[savvej]

If "all flux of primary is linked with secondary" then all flux of secondary is linked with primary. They are one and the same flux. So I don't understand your statement. The number of relative turns between primary and secondary has little to do with the flux linkage between windings. Obviously transformers work and deliver current.

I meant when the load is connected,current flows in secondary and opposing flux is produced in secondary.If no. of turns in secondary are less,then not all the opposing flux will get linked to the core.
Though the flux produced by primary will be mutually linked with secondary,all times whether load or no load.

 

[crutschow]

The amp-turns flux from the secondary will always balances the amp-turns flux from the primary. I don't know why you think all the secondary flux isn't linked to the core. Why should the secondary flux be different form the primary flux? The secondary may have fewer turns (edit: for a lower output voltage than the primary) but it will have more current (for any given load) then the primary so the secondary flux (amp-turns) still balances the primary flux. That's fundamental to the operation of a transformer.