How would a laminated core reduce eddy current loss?

[powersys]

How would a laminated steel core reduce the eddy current loss in a power transformer? Thanks.

 

[A.Anand Srinivasan]

the laminated core means the core is sliced and each piece is laminated from the next and hence it cuts the path of the eddy current with a lamination(insulation).....
though eddy current still exists but the effect is very less.....

 

[sztibi82]

I suggest to use a better core(above 1khz use ferrites). If the cores area is bigger, then loses will be lower.

Also if the plates are thinner, loses are less.

 

[powersys]

Also if the plates are thinner, loses are less.

Could u pls explain why when plates are thinner, losses are less? Thanks.

 

[A.Anand Srinivasan]

actually eddy current forms circular paths and current flows through it.... so when the path is long the power loss is more (long path means more resistance)..... when the plates are made thin the path becomes very small and hence lesser power dissipation....

 

[powersys]

actually eddy current forms circular paths and current flows through it.... so when the path is long the power loss is more (long path means more resistance)..... when the plates are made thin the path becomes very small and hence lesser power dissipation....

In ac apparatus, the cores exposed to alternating fields are laminated or subdivided into thin layers, each electrically insulated from the next, to break the eddy current path up into many short segments. See Figure 1. That in effect places a series of fairly high resistances in that path. Current flow is reduced; losses go down in proportion to the square of that current.
http://findarticles.com/p/articles/mi_qa3726/is_199612/ai_n8755644/pg_2

Would you please explain how we obtain "a series of faily high resistances in that path" after dividing the core into short segments?

Thanks

 

[A.Anand Srinivasan]

the resistance is given by ρ(l/a).... here the length l gets minimized and also area a remains constant and hence the resistance increases leading to more resistance to eddy current...

 

[powersys]

the resistance is given by ρ(l/a).... here the length l gets minimized and also area a remains constant and hence the resistance increases leading to more resistance to eddy current...

Do you mean "length L gets minimized" = "length L gets reduced"? If length L gets reduced, then R=ρ(L/a) should be smaller right?

 

[jallem]

The eddy currents are perpendicular to the B field.
If you laminate in the direction of B then the eddy
currents find a path that is interrupted by series
of thin conductors which are isolated between them.

 

[A.Anand Srinivasan]

see things in the form of a circle.... by length i meant the diameter of the eddy current loop that is formed.... the area depends on the square of the length(diameter) and hence there is a length term coming in the denominator......

so when length is minimised the resistance increases.......

 

[powersys]

see things in the form of a circle.... by length i meant the diameter of the eddy current loop that is formed.... the area depends on the square of the length(diameter) and hence there is a length term coming in the denominator......

so when length is minimised the resistance increases.......

If we refer to R=(ρL)/A, the normal of the A (cross-section area) should in parallel with the direction of current flow, right? The normal of the 'A' described in your last message is pependicular with the direction of current flow. So, do you think we can use the 'A' to calculate resistance against eddy current? Pls correct me if I'm wrong...

 

[A.Anand Srinivasan]

u got me confused for a few minutes.... so i did some referring and look what i found....


Electrons cannot cross the insulating gap between the laminations and so are unable to circulate on wide arcs. Charges gather at the lamination boundaries, in a process analogous to the Hall effect, producing electric fields that oppose further accumulation of charge and hence suppressing the flow of eddy currents. The shorter the distance between adjacent laminations the greater the suppression of eddy currents.

hope it is useful....