i have found very interested concept for calculating losses in winding. The MMF diagram is required. i have found mmf diagram examples on coursera magnetic course and on a ridley engineering website. It looks like they both consider that the core is EE and the windings are both wound around the central leg of the core, but they use strange numering of numbers for some reason. Why are they doing this? this is from coursera

This is from redley engineering

I am realy confused. How to build MMF diagram, which has a 3 layers of primary (foil, 0.44mm of thickness, a little larger than the skin depth 0.29mm) and 2 layers of secondary (foil 2, 1.17mm of thickness, 4 times larger than 0.29mm of skin depth) The primary should be wound around the secondary like this: My diagram Note that secondary winding conducts 2 times current of primary because it is 2:1 transformer. Is my diagram wight or wrong and what is the principle of building the MMF diagram? Why on the pictures i posted this type of layer numbering is used?

P.S > Windings of this transformer are not wound of foil in reality, the foil conductors are just approximation i made for round conductors.

  • \$\begingroup\$ Are you talking about x's and dots in the circles? Or are you talking about why it's "1 2 3" and then "3 2 1"? \$\endgroup\$
    – user103380
    Mar 14, 2018 at 21:16
  • \$\begingroup\$ about both. But why it is 1 2 3 primary and then 3 2 1 secondary if it is E core and the windings are wound around central leg? \$\endgroup\$ Mar 14, 2018 at 21:21

1 Answer 1


The numbers represent the MMF, MagnetoMotive Force, at that radius in the windings. You integrate the total current flowing as you move outwards.

$$MMF(r) = \sum_0^r I(r)$$

In your first diagram, as you move through the three layers of the primary, you have one coil with current emerging from the page, then two, then three. The sections are helpfully labelled \$i\$. Once you start counting through the secondary, in the first secondary section current is going into the page, labelled as \$-i\$, which cancels some of the primary current, so the total current drops to two. As you count through the next two sections, all the current is cancelled, and the MMF drops to zero.

The sections have been labelled with the current in that section, and an indication of the MMF at that radius. Unfortunately, labelling the MMF in the middle of the coils is wrong, there is no consistent way to interpret those numbers as the MMF at the left or right side of the coil. It would have been better to label the seven spaces as 0, 1, 2, 3, 2, 1, 0, rather than label the six coils as they have been.


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