Exam Question

(a) Describe the no-load saturation characteristic of a d.c. generator. (6)

(b) A 400V shunt motor has an armature resistance of 0.3 ohm and a shunt-field circuit resistance of 300 ohm. Calculate the speed attained by the motor when the current taken from the supply is (i) 30A and (ii) 50A. The open-circuit characteristic of the machine, when driven as a generator at 1500 rev/min, is riven by the following figures:

Field cueent (A): 0.25 0.5 0.75 1.0 1.25 1.5

Open-circuit voltage: 220 398 515 598 638 662

Neglect the effects of armature reaction (10)