Evaluation of Insulating Magnetic Materials Composed of Epoxy Resin and Pure Iron Powder for Motor and Reactor Core Applications

Abstract

The insulation and magnetic properties of epoxy composed of pure iron powders were studied as a function of iron powder volume fraction (R_ꜰe) in the range of 0–70 vol% to achieve a good balance between the insulation and magnetic properties. Frequency-dependent impedance measurement revealed that the relative permittivity, ε_r', at 10 kHz increased from 4.2 to 278.4 with increasing R_ꜰe up to 50 vol%. The loss factor, ε_r'', increased from 0.2 to 86.1 and the electric conductivity, σ, increased from 9.9×10^-8 S/m to 4.8×10^-5 S/m at 10 kHz with increasing R_ꜰe up to 50 vol%. The dependence of σ on R_ꜰe was explained by the equivalent serial capacitor-resistor (CR) connection model. The initial maximum relative permeability, μ_{r_max}, increased from 3.7 to 8.9 with increasing R_ꜰe up to 70 vol%. These data were compared with those for the “Reference” sample which has been in practical use in industrial electric machine applications.