Answer Happy

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/rpm and 0.06  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
chopper is employed?
(5 marks)
(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)
(e)
Evaluate the output torque of the motor.
(4 marks)
(f)
Evaluate the motor efficiency.
(2 marks)
(vi) the motor speed in rev/min at one-third torque. (3 marks) 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/rpm and 0.06 92 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) (e) Evaluate the output torque of the motor. (4 marks) (f) Evaluate the motor efficiency. (2 marks) State any assumptions made