Transformer core and magnetic field 1

[Mr zezo]

If primary magnetic flux is totally contained within the iron core then how the secondary winding is being linked or cut by the magnetic field without lines of force cutting the windings? specially when the primary and secondary windings are in different limbs,like single phase transformer.

 

[prc]

In core-type transformers, both primary and secondary windings are placed concentrically over the core. So, both windings are linked by core flux, and voltages are induced in windings. But the current to transfer to the secondary, there should be a linking flux between the windings. This is created in the gap between windings, just as in a solenoid.

 

[Mr zezo]

What about single phase transformer where primary and secondary are in different limbs!?

 

[jghrist]

The flux flows around the core through both limbs.

 

[prc]

If you put primary and secondary on different limbs, at no-load you will get voltage. But once to try to load it you will find secondary voltage simply drops out excess voltage drop.
In single-phase trfs, you may put both windings in parallel or in series in both limbs.

 

[Mr zezo]

that's not my question, my question is if the magnetic field passes through the core then how it linkages with the secondary windings,what I mean like jghrist said the magnetic field passes around the core not inside the core,is it true , it seems logical, IAM not taking about voltage drop here but how the induced voltage appears if the flux is in the core ,how it linked the secondary winding? And in core type transformer you know that same transformer can work step up or step down so what happens when primary windings(which is connected to source) is located directly (firstly) on the core then secondary windings (which is connected to load)above it ? My question here is More related to physical theroy which explains what really happenes or how it really works. All textbooks say that magnetic flux passes through or inside the core and at same time it says emf induced due to flux linkage or cutting the other winding, and here is the confusion here.so what's the shape of the magnetic flux in case using core and without using core, in a coil we know the shape of building and collapsing of magnetic flux then what happens when using core is it still building and collapsing by the same familiar shape around the core or it just passes through the core?

 

[dpc]

It's actually quite an amazing fact that the flux is nearly entirely within the steel core, but a coil wrapped around the core will have a voltage induced. I think we take this for granted when we start getting bogged down in the details of transformers. We know this is what is happening but explaining it in terms of analogies is quite difficult. It is almost like getting wet just from standing next to a pipe with water flowing in it. But that is how it works. I think this is Mr Zero's question. I see no need for snark if someone is simply trying to understand something.

 

[prc]

I do not know what is your understanding of flux linkage. The same flux passes through the center of both windings. This flux makes a closed path by passing through the other limb. If you put the secondary winding just outside the core near to primary winding no flux will pass through the center of the secondary winding and there will be no voltage induced in the secondary winding.
Suppose there is no core inside the winding, but only air. Then a very high current will be required to create flux inside the winding(as air has poor permeability compared to iron). Due to the high exciting current, the load current got from secondary will drastically come down.
The voltage drop I explained as the reason for current not getting from the secondary if you put primary and secondary on different limbs.

 

[Mr zezo]

Flux linkage which I mean is that the flux circular lines Penetrate the other coil(like, flux lines touching the other coil)as shown in attached picture, and also that's the familiar shape of circular flux lines in air , so the confusion here is in transformer core what's the shape of the flux lines in the core and if it inside the core then how it penetrate (touches) the secondary. Take in consideration that the same transformer can work as step up or step down so the arrangements of coils can be changed and also in some single phase transformer if I put primary and secondary windings in two different limbs like the attached picture,

 

[davidbeach]

That's from a text book, not from a real transformer.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[prc]

Many textbooks show such mistakes- putting primary and secondary windings on different limbs. Voltage will be there on secondary. You will not be able to draw current.

https://www.linkedin.com/pulse/misconceptions-transformers-3-p-ramachandran

Flux need not touch the winding. It should pass through the inside of winding and close the path as in your first figure.