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Q4. (a) For a shunt-excited DC motor, aiding with proper equations and drawings, state briefly: (i) The characteristics of motor speed versus armature voltage and load torque; (ii) The two basic motor speed control strategies and their pros and cons. (10 marks) (b) A 50 kW, 250 V, 200 A, 1200 rpm DC shunt generator has an armature circuit resistance (including the brushes) of 0.292. The generator is driven at a constant rotor speed of 1200 rpm and is adjusted to give a rated voltage of 250 V at a full load current of 200 A with a field circuit resistance of 50 2. Assume that the generator is linear- excitation at the constant speed, aiding with the equivalent circuit, determine: (1) The field current, armature current and generated voltage when the generator is full-loaded at rated voltage and current; (ii) The field current and the field circuit resistance setting for the generator to deliver a load current of 100 A at 250 V. (15 marks) 3