4.6.1 Self-inductance arrangements Neglecting the iron loss in the magnetic loop and assuming the air gap is small, then the total reluctance of the magnetic circuit 126 R (425) A where / length of the iron circuit ( m u=permeability of the iron core f /m A =crOSs-sectional area of the iron, A=ab(m) length of the air gaps() Ho=permeabiltiy of free space( vacuum)Ao =4T X10(H/m Ao =cross-sectional area of the air gap(Neglecting the iron loss in the magnetic loop and assuming the air gap  is small, then the total reluctance of the magnetic circuit: 0 0 2 A A l Rm    = + （4.25） where l = length of the iron circuit (m )  = permeability of the iron core (H / m ) A = cross-sectional area of the iron, ) 2 A = a b（m  = length of the air gaps (m )  0 = permeabiltiy of free space ( vacuum) 4 10 ( / ) 7 0 H m −  =   A0 = cross-sectional area of the air gap ( 2 m ) 4.6.1 Self-inductance arrangements