Hysteresis

BH Magnetization Curve

Magnetic Induction - h1011v1_65

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MAGNETIC CIRCUITS Basic Electrical Theory The permeability (µ) of a magnetic material is the ratio of B to H. Equation (1-18) is the mathematical representation for magnetic material permeability. (1-18) µ B H The average value of permeability is measured where the saturation point, or knee, is first established. Figure 27 shows that the normal or average permeability for the two irons as follows. µ soft iron 1 = = = 1 x 10^-4 B H 0.2 2000 (T m) At µ soft iron 2 = = 6 x 10^-5 B H 0.3 5000 (T m ) At In SI units, the permeability of a vacuum is µ_o = 4 p x 10^-7 H/m or 1.26 x 10^-6 or T-m/At. In order to calculate permeability, the value of relative permeability µ_r must be multiplied by µ_o. Equation (1-18) is the mathematical representation for permeability. µ = µ_r x µ_o (1-18) Example: Find the permeability of a material that has a relative permeability of 100. µ = µ_r x µ_o = 100 (1.26 x 10^-6) = 126 x 10^-6 (T m) At Hysteresis When current in a coil reverses direction thousands of times per second, hysteresis can cause considerable loss of energy. Hysteresis is defined as "a lagging behind." The magnetic flux in an iron core lags behind the magnetizing force. ES-01 Page 40 Rev. 0

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