Flux density is defined as flux per unit area. i.e. Bm=
ϕ
A
Where ϕ= flux per pole A= area of core Size of the machine is directly proportional to area i.e. size of machine ∝ area of machine ∝
1
Bm
Hence with the increase in magnetic flux density, the size of the machine decreases. As the machine size decreases, p.u. armature resistance increases and p.u. synchronous reactance decreases.