How to show laminations minimizes eddy current?

AI Thread Summary
Lamination in transformers effectively reduces eddy current losses, which are a significant source of energy loss. The discussion highlights the need for a theoretical approach to demonstrate that energy loss in laminated materials is less than in solid materials, despite the same cross-sectional area. Faraday's Law is referenced as a key principle for understanding how dividing a large area into smaller insulated laminations affects induced voltage and eddy currents. Additionally, the conversation touches on the impact of silicon in laminated iron, which improves electrical properties and further reduces eddy currents. The importance of experimental methods versus theoretical understanding in this context is also debated, emphasizing the established use of lamination in transformer design.
kelvin490
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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)?
 
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kelvin490 said:
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:

BHCurve.gif


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.
 
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kelvin490 said:
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? :smile:
 
berkeman said:
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? :smile:

I don't know...
 
berkeman said:
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

:smile:

Path lengths are different, so the integral for one laminate is small. If I add it up, is it smaller than one large piece?
 
kelvin490 said:
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 _____ ...
 
@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.
 
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Hesch said:
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?
 
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  • #10
Hesch said:
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.
 
  • #11
berkeman said:
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?
 
  • #12
kelvin490 said:
Area?

Yes! :smile:

The area ratios how with the circumference?
 
  • #13
berkeman said:
Yes! :smile:

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.
 
  • #14
kelvin490 said:
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?
 
  • #15
berkeman said:
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.
 
  • #16
kelvin490 said:
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
 
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  • #18
BTW @kelvin490 -- Can you guess why higher frequency ferrite transformers do not have laminations? :smile:
 
  • #19
berkeman said:
BTW @kelvin490 -- Can you guess why higher frequency ferrite transformers do not have laminations? :smile:

High reactance?
 
  • #20
kelvin490 said:
High reactance?

No, not reactance...
 
  • #21
berkeman said:
No, not reactance...

low current.
 
  • #22
kelvin490 said:
low current.

Nope. What property of a magnetic material would minimize eddy currents?
 
  • #23
berkeman said:
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.
 
  • #24
kelvin490 said:
High permeability.

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

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