B3. A separately-excited D.C. motor is driven by a step-down chopper from a 850 V D.C. supply. Given the back e.m.f. con

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B3 A Separately Excited D C Motor Is Driven By A Step Down Chopper From A 850 V D C Supply Given The Back E M F Con 1 (60.54 KiB) Viewed 18 times

B3. A separately-excited D.C. motor is driven by a step-down chopper from a 850 V D.C. supply. Given the back e.m.f. constant and armature resistance of motor are 0.5 V/1pm and 0.06 12 respectively. The motor draws an average armature current of 250 A from the supply and the input power is 100 kW. Given that the armature current is continuous and ripple free. (a) Draw the circuit diagram of the driving system. Which class of (5 marks) chopper is employed? (b) Sketch the waveform of output voltage. (2 marks) (c) Evaluate the duty cycle of the chopper. (2 marks) (d) Evaluate the motor speed in rev/min. (5 marks) Evaluate the output torque of the motor. (4 marks) (f) Evaluate the motor efficiency. (2 marks)