For a transformer, what kind of material will you choose- the one with small hysteresis area or the one with the big one?
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• Hysteresis: -

  • Hysteresis is the dependence of the output of a system not only on its current input, but also on its history of past inputs.

  • The dependence arises because the history affects the value of an internal state

  • To predict its future outputs, either its internal state or its history must be known.

• Hysteresis Loop: -

• The above figure shows the behavior of a ferromagnetic core subjected to cyclically varying magnetic field.

  • Initially, the core is demagnetized and the strength of magnetic field “H” is set to zero. Thus point “O” marks the starting point of the curve.

  • On increasing magnetic strength the magnetic induction (B) increases non-linearly, as shown, up to point P, after which it remains constant.

  • Thus, point P is known as the saturation point.

  • On reducing “H” to zero, the core still remains magnetized. The residual value of “B” at point Q is called remnant induction.

  • On further reduction of “H” (i.e. increasing “H” in reverse direction), at point R, the core gets completely demagnetized.

  • The value of magnetic strength at that point is called coercive field.

  • As the magnetic field increases in the negative direction, again the magnetic induction appears to remain constant after a certain point S.

  • This is the saturation point in the negative direction.

  • Similarly, points T and U corresponds to points Q and R respectively as the value of “H” is increased reaching point P again.

  • The full cycle of magnetization and demagnetization of core is termed as Hysteresis loop.

(Note: If the time is less and the weightage for the question is not much, just mention the points and write their significance. No need to explain the process)

• Significance of the Area Enclosed: -

The area enclosed by the Hysteresis loop represents the energy loss per unit volume of the material per unit cycle.

• Material for transformer: -

For transformer cores, soft magnetic materials are used which has a smaller Hysteresis area.