Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

L11 magnetic circuits

3,810 views

Published on

Published in: Technology, Business

L11 magnetic circuits

  1. 1. MAGNETIC CIRCUITS
  2. 2. ELE101 / 102 Dept of E & E Engg, MIT Manipal 2 Terminologies Magnetic flux (Φ): No. of magnetic lines of force created in a magnetic circuit Unit is Weber (Wb) Flux Density: (B) No. of magnetic lines of force created in a magnetic circuit per unit area perpendicular to the direction of flux lines B = Φ/A Unit is Weber/sq.m (Tesla)
  3. 3. ELE101 / 102 Dept of E & E Engg, MIT Manipal 3 Terminologies Magneto motive force: (F) Force which drives or tends to drive the magnetic flux through a magnetic circuit MMF = No. of turns*Current = N I Unit is AT (ampere - Turns) Magnetic field strength: (H) The magneto motive force per meter length of the magnetic circuit H = (N I) / L Unit is AT / meter
  4. 4. ELE101 / 102 Dept of E & E Engg, MIT Manipal 4 Permeability [μ] A property of a magnetic material which indicates the ability of magnetic circuit to carry electromagnetic flux. Ratio of flux density to the magnetizing force, μ = B / H Unit: henry / meter Permeability of free space or air or non magnetic material Relative permeability [μr] : Terminologies mH /104 7 0 − ×= πµ rµµµ 0=
  5. 5. ELE101 / 102 Dept of E & E Engg, MIT Manipal 5 Terminologies Reluctance [S] It is the opposition of a magnetic circuit to setting up of a magnetic flux in it. ‘S’ is called the reluctance of the magnetic circuit Reluctance = mmf / Magnetic flux Unit: AT / Wb         ==       =       === ===== A l ; S F A l F F l A Hence; l A Hl BA F HB;HlmmfF;BAFlux r r rr µµ µµ φ µµ φ µµφ µφ 0 0 00 Swhere
  6. 6. ELE101 / 102 Dept of E & E Engg, MIT Manipal 6 Magnetic circuit The complete closed path followed by any group of magnetic lines of flux is referred to a magnetic circuit VI R Equivalent electrical circuit
  7. 7. ELE101 / 102 Dept of E & E Engg, MIT Manipal 7 Analogy with Electric circuits Electric circuit Magnetic circuit Similarities: Emf, volt mmf, ampere Turn Current, ampere flux, weber Resistance, ohm Reluctance, A / Wb Current density, A / m2 flux density, T or Wb / m2 Conductivity Permeability Difference:  Current actually flows flux is created, but does not flow  Circuit may be open or Circuit is always closed closed
  8. 8. ELE101 / 102 Dept of E & E Engg, MIT Manipal 8 Leakage flux Leakage Flux : The flux that does not follow the intended path in the magnetic circuit Leakage flux factor λ Fringing: Effect of spreading out of flux in the air gap Totalflux(fluxinthe iron path) Useful flux(flux in the airgap) =
  9. 9. ELE101 / 102 Dept of E & E Engg, MIT Manipal 9 Magnetic circuits losses Two types of losses: Hysteresis losses Eddy current losses
  10. 10. ELE101 / 102 Dept of E & E Engg, MIT Manipal 10 B-H Curve & Hysteresis loss a b c d Residual magnetism Hysteresis loss: Magnetic hysteresis: Lagging of magnetization or flux density behind the magnetizing force. Hysteresis loss = ή (Bmax)1.6 J / m / cycle Where ή is Steinmetz hysteresis co-efficient B-H Curve:
  11. 11. ELE101 / 102 Dept of E & E Engg, MIT Manipal 11 Eddy current loss Eddy current: The varying flux in the Magnetic core induces emf and hence Current Eddy current results in Loss of power, Heating of the material

×