# Reducing equivalent self inductance of an inductor

Let's say I have a coil of N turns and it is wound on a rectangular core and when we connect a voltage source through both terminal of coil flux is generated in core , now I wanted to reduce that flux as minimum as possible (zero would be Even better) .

Although it can be achieved easily if we are allowed to cut the winding and then wound such a way that net mmf cancel each other

But What if we are not allowed to cut the winding ,is it possible reduce flux up to zero ?

First thought comes to mind that we can wound N/2 and N/2 such that flux will cancel each other but I'm​ not sure it will work because how can a series Inductance reduces (L=L/2-L/2) because (L=L1+L2) series connection are additive

Is above method works or not ? Or it is impossible to cancel or reduce flux because of series connection of winding?

• You could replace the inductor with a straight wire; you won't reduce the inductance much below that. But I have a feeling you're asking something else like how to keep (unspecified property of) an inductance while reducing or eliminating the associated inductance. Or flux. Or something. Dec 5, 2020 at 18:48
• Sounds like an XY problem to me. Dec 5, 2020 at 18:49
• @Brian Drummond, exactly ! ( you're asking something else like how to keep (unspecified property of) an inductance while reducing or eliminating the associated inductance. Or flux. Or something) Dec 5, 2020 at 18:56
• ... but you're still not telling us what property you want to keep and exactly what you want to reduce. Dec 5, 2020 at 22:13

You are correct that you can reduce the flux in the core by having half of the turns go in one direction and half of the turns go in the opposite direction. Can you reduce it to 0? Well that depends upon what you mean.

Because the wires with current flowing one way are physically distant from the wires flowing in the opposite direction, each will produce flux. At a distance those fluxes will "cancel" each other out. However, there will be some flux near each wire.

If the stars in heaven are aligned perfectly, none of this "leakage" flux will make a loop around the window of the core. For all practical purposes, you could say that the flux in the core is 0. Of course, there is bound to be be some imbalances. The spacing between wires will vary at least microscopically from one place to another, so the flux around the core window may not be mathematically 0, even if it is 0 for practical purposes.

Such a coil, by the way, would not be useful as an inductor, because an inductor works by generating flux!

Edit:

"how can a series Inductance reduces (L=L/2-L/2) because (L=L1+L2) series connection are additive"

One can add the inductance values of two inductors wired in series, only if the inductors are magnetically isolated. When inductors coils are coupled magnetically, they form a transformer.

If two "identical" coils are wound on a core, and wired so that they generated flux in the same direction, the inductance would not be increased by a factor of 2, but by a factor of 4! (Inductance generally is proportional to the number of turns squared). Magnetic coupling matters in problems like these.

• Thanks for answer ,but how can Inductances get subtracted instead of addition because circuit is in series ? Dec 5, 2020 at 18:54
• Although the turns in each direction are electrically in series, they are not magnetically isolated, but magnetically coupled. What you have is more of a 1:1 transformer, wired so that the voltages induced in each winding cancel each other out. Dec 5, 2020 at 18:59
• I have expanded my answer a bit. Dec 5, 2020 at 19:08
• So what I understand by your answer that in such cases (magnetically couple series circuit ) approximately zero equivalent Inductances is possible i.e Leq =L/2+L/2 - M =0 (if coupling is perfect i.e M=L)?? Dec 5, 2020 at 19:16