- Question 4 APART (Total 20 Marks) A 200-V DC shunt motor has a field resistance of 200 2 and an armature resistance of 0.5 2. On no-load, the machine operates with full field flux at a speed of 1,000 rpm with an armature current of 4A. Neglect armature saturation and armature reaction. a) If the motor drives a load requiring a torque of 100 N.m, find the armature current and speed of the motor T b) If the motor is required to develop 10hp at 1200 rpm, compute the required value of external series resistance in the field circuit. Question 5 E (Total 20 Marks) A dc series motor is driving a fan-type load. The armature and field resistance of the motor are 292 and 302, respectively. When the terminal voltage of the motor is 200V, the motor speed is 250 rpm and the armature current is 10A. N Assume that the motor operates at the linear region of the field current characteristics and 12 the torque is constant.. a. b. C. Calculate the terminal voltage needed to reduce the motor speed to 100 rpm. Calculate the terminal voltage needed to reduce the motor speed to 0 Sketch the speed torque characteristics and show all operating conditions. Question 6 4 a. No losses Eff (Total 20 Marks) Comment on the speed control of induction motors by changing the supply frequency: How this control can be achieved; advantages and disadvantages of this method b. How it is effecting: 2 i. the synchronous speed 2, ii. The maximum torque 2. ii iii. The starting torque ns Tmax t = 1st & c) Use the electrical drive formula to explain the limitations on the speed control of Induction Motors by changing the frequency 6 d) Show on the speed torque characteristics, how the voltage/frequency control can solve the problems related to the frequency control of Induction Motors diffrent.