Electrical Laminations..

Laminations are used in electro-magnetic devices, transformers, motors etc... They are used to restrict the electrical conductance of the core to reduce core losses, as well as to increase the magnetic permeability of the core. I think that's all I can say in answer to your question, could you be a little more specific? John.

thnx for the info...so these would be sort of outer covering or sheets ...so they r made up of steel rite..r there any specific standards of material which helps in reducing the losses to larger extent...

Yes they would be made from special alloy steel to suit the application and frequency of use etc... From what I understand they are usually 'coated' with an oxide layer to prevent circulating currents causing power loss, when they are stacked side by side... John.

Stamping out, stacking, and pinning (bolting or rivetting) a metallic core using sheet material is far more cost effective (cheaper, easier, faster, less capital intensive, less laborious, less wasteful...) than attempting to cut, forge, mold, and/or machine (etc.) a solid core from a billet--the larger the core the more cost effective. So, your question is equally apropos without mention of "lamination." Lamination itself is simply the way cores are generally fabricated, nothing more.

As Electroman said the laminations are there to increase the efficiency of the device. What happens is that if you use a solid core the magnetic filed induces small circulating electric currents called eddy currents in the core. These eddy currents reduce the overall efficiency by firstly opposing the magnetic flux and secondly by heating the core. By constructing the core from laminations that are insulated from each other you can minimize the eddy currents as they cant flow between the layers and thus you improve the overall efficiency of the device.

The type of metal that the core is made of is also critical as it needs to have as little residual magnetism as possible. In the diagram below the magnetic flux in the core is the vertical axis and the current in the exciting coil is the horizontal axis.

Imagine now that as the current increases in the forward part of the AC cycle the magnetic flux will increase until the core becomes saturated (point a) as shown by the red line. As the current decreases the magnetic flux relaxes as shown by the green line but as you can see when the current returns to zero (point b) there is still a residual amount of flux left in the core. As the reverse part of the AC cycle starts it now needs to overcome this residual magnetism shown in purple before the magnetic flux reverses (point c) then caries on till it saturates in the opposite direction (point d). As you can see the greater the residual magnetism that the core has the more energy will be expended overcoming it before the core can reverse its field and start working in the opposite direction. This residual energy loop is called hysterisis and you will come across it many times in engineering.

To sum it up the material used to construct the core need to not only be as permeable to a magnetic field as possible but also have as little residual magnetism as possible.

I hope that helps.

Wow!! couldn't have put it better than you Masu!

I don't suppose you could explain why the higher the frequency of operation, the thinner the laminations need to be... Until at high frequencies a compressed powder (ferrite) needs to be used??

I think my explanation isn't complete and wouldn't be as concise as your answer above!

John.

Electrical laminations are sheet steel made of alloys having high silicon low carbon content. They are coated with some vernish. They may be grain oriented or non grain grain oriented depending on the use. These material are mainly used for electric motor and transformer cores. They have good magnetic properties like high permeability.

Amir