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i have noticed that all of the transformer/motor/alternator/electric actuator have a stack of metal for stator ( or where winding is done. ). why is that needed ? can same thing not achieve by using a block of metal ? i guess its because of performance. how much performance can possibly lost ?

why motor or alternator has stack of metal plates instead of simple block of metal ? what is the difference between the two ?

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FYI they are called laminations (you'll hear "lamination stack" or "lam stack" in the trade) and they're for keeping low core losses by interrupting induced eddy currents and keeping them confined to a single lamination where the loop area is small.

Also, there's an additional practical reason for using laminations: you can easily use the same lamination design for different length stacks just by using more or fewer laminations for a shorter/longer stack. A solid core would require different manufacturing steps for different designs.

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  • \$\begingroup\$ That's what I was taught in my power engineering courses as well. \$\endgroup\$ – pfyon Nov 3 '11 at 18:26
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For transformers I can see two reasons.

Instead of having one "E" block and one "I" block thinner metal plates are interleaved with each time an "E" element on one side followed by an "I" element. That way there's a better contact between the parts, and air gaps are avoided.

Secondly, the magnetic field would cause a high eddy currents in the core, which would cause heat losses. By dividing the core in smaller, mutually insulated parts, this is largely prevented.

Possibly the same arguments go for motors and alternators as well.

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  • 4
    \$\begingroup\$ preventing eddy currents is the primary reason \$\endgroup\$ – Jason S Nov 3 '11 at 18:02

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