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What is the differnce between a transformer having ferrite core and another transformer without any core (air core transformer).How these two affects the output power and leakage flux??

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  • \$\begingroup\$ Why the downvotes? Sounds like a reasonable question to me. \$\endgroup\$ Commented Jun 18, 2013 at 12:40
  • \$\begingroup\$ I agree @OlinLathrop \$\endgroup\$
    – Andy aka
    Commented Jun 18, 2013 at 12:40
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    \$\begingroup\$ Question doesn't show any research effort. \$\endgroup\$ Commented Jun 18, 2013 at 14:42

2 Answers 2

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The main reasons ferrite cores are used are: -

  • They contain the magnetic field better than air preventing coupling to other circuits
  • Higher value inductances can be made with much less copper - trading off copper loss with core loss gives the designer more options.
  • Coupling of two or more windings is more effective (should this be required)
  • Ferrite solutions (when applicable) are usually physically smaller than air.

The main reasons ferrite cores are not used are: -

  • Permeability drifts with temperature hence air cored inductors are more stable in some applications
  • Air cores don't saturate and produce 3rd order harmonics like ferrite. Useful, unless you are designing a saturable reactor of course.
  • For tuned circuits in the VHF and above, ferrites are too lossy in some applications.

These are the main pros and cons.

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Consider the two scenarios.

Without a core, the magnetic field strength is determined by #loops and the current (And many other factors - shape, design, resistance, but we're assuming they're identical for both transformers)

With a ferromagnetic core (Like e.g. Ferrite), applying a magnetic field will induce magnetism in the core, which will increase the magnetic field strength, which will induce magnetism in the core, which will...

As such, you can get a higher field strength from the same current with a ferromagnetic core.

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  • \$\begingroup\$ what about flux leakage?? \$\endgroup\$
    – Atom
    Commented Jun 18, 2013 at 12:26
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    \$\begingroup\$ Magnetic field strength is not increased with a ferrite core - the core will reduce current due to its increase in permeability. Flux density will increase of course. \$\endgroup\$
    – Andy aka
    Commented Jun 18, 2013 at 12:39
  • \$\begingroup\$ @Andyaka Yes,But there is a little bit confusion about leakage flux.I think that in air core transformer its not easy to control the leakage flux.So is there any way to control the leakage flux? \$\endgroup\$
    – Atom
    Commented Jun 18, 2013 at 12:49
  • \$\begingroup\$ @SHASWAT - see my answer - controlling leakage flux is much harder in air cores unless the frequency is high and conductive screens can be used. \$\endgroup\$
    – Andy aka
    Commented Jun 18, 2013 at 12:53
  • \$\begingroup\$ @Andy aka: I am assuming fixed current. \$\endgroup\$
    – shieldfoss
    Commented Jun 18, 2013 at 13:00

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