In Fig Q3, a D.C. shunt motor takes an armature current laj of 30A from a 500V D.C. Q3 supply. It runs at N1 = 1500 rev/min. Its total armature resistance Raj is 0.22. The motor speed is decreased by the use of armature resistance control. (a) Calculate the induced emf El of the motor at N1 = 1500 rev/min. (5 marks) (b) Calculate the induced emf E2 of the motor if its speed is decreased to (5 marks) N2 = 1200 rev/min. (c) Assume Ta N where T is the motor torque, N is the motor speed. (5 marks) Calculate the new armature current la2 of the motor when speed is N2 = 1200 rev/min. (d) Based on part (c), calculate the value of additional resistance Radd (5 marks) required in series with the Ra, = 0.2 0 resistance in the motor armature circuit to decrease the motor speed to N2 = 1200 rev/min. Iaj=30A 0.22 (Constant flux 0) 500V Shunt E1 1500 rpm Field Fig Q3 Q4 (a) A 3-phase induction motor having a synchronous speed of 1200rpm draws 80kW from a 3-phase feeder. The copper losses and core losses in the stator amount to 5kW. If the motor runs at 1152rpm, calculate: the rotor input power; (ii) the rotor copper losses; (iii) the gross mechanical power output; (i) (2 marks) (2 marks) (2 marks) (vi) the net mechanical power with knowing that the windage and (2 marks) friction losses are 2kW; (v) the efficiency of the motor. (2 marks) (b) Compare the brushed motor (DC motor) and a brushless motor (10 marks) (induction motor) in FIVE aspects.