A cross-section of the magnetic structure of a dc machine is shown in Fig.3. There are four identical poles carrying identical coils with the same number of turns and current. The stator poles and rotor are made of sheet steel with a relative permeability of 3800. The stator is made of cast steel with a relative permeability of 1500. The following dimensions are available

Rotor diameter =18 cm

Rotor axial length = 10 cm

Pole axial length = 10 cm

Pole circumferential width = 8.5 cm

Pole height = 9 cm

Stator yoke mean diameter = 42 cm
Stator yoke cross-section = 14 x 6 cm

Air-gap length = 1.5mm

It is required to:

b. Determine the mmf per pole required to produce a flux density of 0.9 T in the air gap.

Roter Fig. 3 Air gep 4/2 N 6/2 Stator -Field col