Looking for sketch of electomagnetic field of a transformer

[volker]

Hello,

Does anyone have a sketch - or know a web page where to find any - showing the electromagnetic field created by a transformer ?

The transformer I am thinking of has a normal M102 core.

The core looks like a closed 'M'
(top view, m means 'material of the core'🙂

mmmmmm
m....m....m
m....m....m
mmmmmm

and the winding is around the middle part.

So, it is a standard transformer.

Where would the electric flux lines start and where would they close ?

Thanks a lot for your efforts,

Volker.

 

[J Epstein]

The flux lines will travel within the core material.

using your drawing they will form two closed "circles" and look like this:

00

This is why the center of the M laminations is twice as thick as the sides: there is twice the flux through the center.

 

[volker]

Hello J Epstein !

Thanks for the reply !

I assume that the field of the shape 00 is parallel to the drowing of the 'm'. I assume that it is parallel to the surface of this screen.

But what about the field that is perpendicular to the pane ?

Volker.

 

[J Epstein]

That's why cores use thin laminations: they are designed to keep the lines of flux in the plane of the laminations and not allow them to deviate from this plane. In the ideal case, there is no line of flux in any other direction.

In reality, there are fringe fields and eddy currents in the laminations which reduce the magnetic efficiency of the core. This is still much more efficient magnetically than air.

In an air cored transformer I think the lines of flux would look like the above example except they would be rotated about the central axis, so they would look like a donut instead of a flat 00.

(There are also some weaker fields that radiate out beyond these.) This is hard to draw in text, but I bet there is a reference on the web you could look at.

-j