How to show laminations minimizes eddy current?

[kelvin490]

In transformer, lamination is an effective method to minimize eddy current and thus energy loss. I just wonder how can we show that the energy loss due to eddy current in those laminates is added up to be less than that without lamination (suppose the total cross sectional areas are the same)?

 

[Hesch]

how can we show that the energy loss due to eddy current in those laminates is added up to be less than that without lamination (suppose the total cross sectional areas are the same)?

There are also losses in iron due to magnetic hysterisis in iron:

I think the hysterisis losses will be the same, laminated iron or not. But anyway:

Connect the (unloaded) transformers to the mains supply. Measure their power consumptions by a watt-meter, or measure the temperature gradients of the cores.

 

[berkeman]

In transformer, lamination is an effective method to minimize eddy current and thus energy loss. I just wonder how can we show that the energy loss due to eddy current in those laminates is added up to be less than that without lamination (suppose the total cross sectional areas are the same)?

What is the Relevant Equation for calculating the current in a loop with a changing magnetic field piercing the loop? What part of that equation are you affecting when you divide up a piece of metal into laminations that are insulated from each other?

 

[kelvin490]

What is the Relevant Equation for calculating the current in a loop with a changing magnetic field piercing the loop? What part of that equation are you affecting when you divide up a piece of metal into laminations that are insulated from each other?

I don't know...

 

[berkeman]

I don't know...

Start with Faraday's Law, and see if you can figure out what happens when you replace one large area with many small ones that are insulated from each other...

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html

 

[kelvin490]

Start with Faraday's Law, and see if you can figure out what happens when you replace one large area with many small ones that are insulated from each other...

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html

Path lengths are different, so the integral for one laminate is small. If I add it up, is it smaller than one large piece?

 

[berkeman]

Path lengths are different, so the integral for one laminate is small. If I add it up, is it smaller than one large piece?

That may be one effect, but there is a more important one. Under Faraday's Law, when you have an area that has a changing flux, that induces a voltage around the loop area, which generates an eddy current in this case. Since the induced voltage and resulting eddy current depends on the _____ ...

 

[Hesch]

@kelvin490: You must regard that laminated iron is mixed up with silicon. This silicon decreases the magnetic proporties a little, but the electrical proporties (conductivity ) are decreased much more, thereby lowering the Eddy current.

So be cautious analysing the results of the measurements.

 

[Hesch]

So be cautious analysing the results of the measurements.

Solution to this problem:

Build a cube of laminated iron and make some coil that fits this cube. ( Saw a piece of the centerleg out of some transformer core ).

Now you induce a magnetic (AC) field parallel to the lamination, thereafter (moving the coil) induce the magnetic field perpendicular to the lamination.

Your measurements will be different ( I promise ). Think about why?

Is the magnetic field in a transformer parallel or perpendicular to the lamination?

 

[kelvin490]

Solution to this problem:

Build a cube of laminated iron and make some coil that fits this cube. ( Saw a piece of the centerleg out of some transformer core ).

Now you induce a magnetic (AC) field parallel to the lamination, thereafter (moving the coil) induce the magnetic field perpendicular to the lamination.

Your measurements will be different ( I promise ). Think about why?

Is the magnetic field in a transformer parallel or perpendicular to the lamination?

Thanks for the answer. But I am not asking for experimental method to show they are different. Lamination has been used in transformers for years, why do I need experimental method to prove it?

What I ask is a theoretical approach.

 

[kelvin490]

That may be one effect, but there is a more important one. Under Faraday's Law, when you have an area that has a changing flux, that induces a voltage around the loop area, which generates an eddy current in this case. Since the induced voltage and resulting eddy current depends on the _____ ...

Area?

 

[berkeman]

Area?

Yes!

The area ratios how with the circumference?

 

[kelvin490]

Yes!

The area ratios how with the circumference?

But we need to show their energy loss added up to be smaller than that in a larger, undivided area.

 

[berkeman]

But we need to show their energy loss added up to be smaller than that in a larger, undivided area.

So this is schoolwork?

And if so, why haven't you been studying Faraday's Law as part of the preparation for this homework question?

 

[kelvin490]

So this is schoolwork?

And if so, why haven't you been studying Faraday's Law as part of the preparation for this homework question?

It's not HW.

 

[Hesch]

What I ask is a theoretical approach.

If you google: eddy+current+losses you will find something like this: [/PLAIN]

http://www.nptel.ac.in/courses/108105053/pdf/L-22%28TB%29%28ET%29%20%28%28EE%29NPTEL%29.pdf

 

[kelvin490]

If you google: eddy+current+losses you will find something like this:
[/PLAIN]
http://www.nptel.ac.in/courses/108105053/pdf/L-22(TB)(ET) ((EE)NPTEL).pdf

Thx

 

[berkeman]

BTW @kelvin490 -- Can you guess why higher frequency ferrite transformers do not have laminations?

 

[kelvin490]

BTW @kelvin490 -- Can you guess why higher frequency ferrite transformers do not have laminations?

High reactance?

 

[berkeman]

High reactance?

No, not reactance...

 

[kelvin490]

No, not reactance...

low current.

 

[berkeman]

low current.

Nope. What property of a magnetic material would minimize eddy currents?

 

[kelvin490]

Nope. What property of a magnetic material would minimize eddy currents?

High permeability.

btw, could you help me on the Ampere's law problem in another thread? May be it is a stupid question but I have no idea how to solve that problem.

 

[berkeman]

High permeability.

Nope. Try googling Ferrite Transformer Eddy Currents -- the first hit on the list for me is a wikipedia article that explains it.