A separately excited wound field DC motor operates with an armature supply voltage of 280 Volts. The field current suppl

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A separately excited wound field DC motor operates with an
armature
supply voltage of 280 Volts. The field current supplied to the
field windings is,
under normal operation, equal to 𝑖𝑓 = 1.0 A, and the resulting
no-load speed
is 2100 rpm. The armature resistance is 1.0 , and the full-load
developed
torque is 22 Nm.
(i) Determine the value of the product 𝐾𝜙𝑓 and the full-load
armature current 𝑖𝑎 under the conditions described
above.
(ii) Determine the full-load speed of the motor in rpm under
the conditions described above.
.
(iii) If the field current is reduced to 0.9 A, but the
developed
torque remains unchanged, calculate the new full-load
speed of the motor in rpm. Hint: Assume that the field
flux 𝝓𝒇is proportional to the field current 𝒊𝒇.