Behavior Of Magnetic Flux

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www.phy-astr.gsu.edu%2Fhsu%2FLCh23.pdf

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I dont think the flux can get higher. It will alternate corresponding to the current.

I think it might become hysterical and suffer a meltdown...

The amount of magnetic flux is proportional to the number of "Ampere turns", i.e., the number of amperes x number of winding turns. So if you connect the windings in opposition, the number of ampere turns is the difference in the number of turns x the current in amperes.

The parameters involved in calculating the flux are the length of the magnetic circuit and the permeability of the core. The amount of flux is roughly proportional to the permeability x the number of ampere turns (in this case, difference) divided by the length of the magnetic circuit (distance around the magnetic core).

"1) would the resultant flux be that of the stronger?"

There isn't a single 'resultant flux.' In all cases the flux density will vary spacially and temporally throughout the volume of the core and in the volume around it. There will be regions where the flux is highest and, because the windings are acting in opposition, regions where it is zero. Where these regions are depends heavily on core geometry, turns ratio, etc.

"2) would core saturation comes into play?"

If the current is high enough, yes, parts of the core will saturate.

If the flux was a doughnut would it be frosted or jelly?

Honey glazed.

Europium mkII has wisely pointed out that it is spatially and temporally complicated. However, so long as you don't look too closely at the lamination corners, etc, you can say that the flux cancels to (approximately) 0. This is the principle of the bucking coils used in long-ago radio sets. You can most easily see this effect in a secondary coil, where you see the induced voltage go to 0. Now, before you try this, it is very easy to get what amounts to a shorted turn, and the resulting heat will ruin your day, so try this first with high impedance, low voltage transformers.

Core saturation will not be a factor if everything is nice and straightforward.

A toroid core (@lyn: blueberry) is the simplest closed form. I might also add that, in my previous post, there will regions in which the flux is a *minimum*, not necessarily zero (at times other than current zero-crossings and neglecting hysteresis)

There are certain data missing in your question. When you say that you allow A/C to flow in both (primary and secondary) coils, you do not specify the amount of current. Pl. specify the applied voltage.

1. If the current amount is same in both coils, then High voltage winding will provide higher amp turn as it has higher turns. In that case flux will be decided by vectorial difference of amp turn provided by both the windings and off course the dimensions and magnetic properties of the core material.

2. In case the voltage applied to the windings is proportional to respective number of turns, then both the amp turns would cancel each other and the resultant amp turns would be zero. Then no flux would be established in the circuit and the current drawn would be decided by electrical resistances of the windings and the applied voltage. This means that heavy current would pass (assuming that winding resistance is small). As no flux is set up, there is no question of saturation in the core iron.

Hi Guys,

Thank you all very much for responding to my post and for your valuable input and also for the humor! - it's good medicine, they say.

Now, I would like to be able to;

1) calculate/determine the size Laminated Core needed to carry the flux that would be involved, so as to avoid saturation,

2) convert ampere-turn (on the Laminated Core) to magnetic field strength.