Reg No.:

Max. Marks:

10

11

DD6811 Pages: 2

Name:

a)

b)

a)

b)

a)

APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
SIXTH SEMESTER B.TECH DEGREE EXAMINATION, APRIL 2018

Course Code: EE308
Course Name: ELECTRIC DRIVES (EE)

100 Duration: 3 Hours
PART A
Answer all questions, each carries 5 marks. Marks
Draw the block diagram of a closed loop speed control of an electric drive. (5)
Derive the speed torque characteristics of DC separately excited motor. Draw (5)
its speed torque characteristics for variable armature resistance.
Draw the circuit diagram of a class-C chopper fed DC motor. Draw its V/I (5)
characteristics.
Draw and explain the speed torque characteristics of a variable stator voltage (5)
controlled induction motor. Why stator voltage control is not suitable for
speed control of induction motor with constant load torque.
What are the different methods for obtaining variable output voltage from an (5)
inverter? Explain.
What is field oriented control of induction motor? Why it is superior to other (5)
types of speed control?
Explain power and torque capability curves of a synchronous motor drive. In (5)
variable frequency control of synchronous motor drive, why V/f ratio is
maintained constant upto base speed and voltage constant above base speed.
Draw the bock diagram of microprocessor based control of permanent magnet (5)
synchronous motor drive
PART B
Answer any two full questions, each carries10 marks.
Differentiate between passive and active load torques. Give examples of each. (3)
A motor when operating in quadrant I and II has the characteristic T= 400 — (7)
0.4N Nm, where N is the speed in rpm. The load which is coupled to the
motor is an active load with the characteristic, | = +200 Nm. Calculate the
motor speeds for motoring and braking operation in the forward direction.
When the drive is operating in quadrant 111 and IV, motor has the
characteristic, T= - 400 - 0.4N Nm. What will be the equilibrium speed in
quadrant III?
State and explain how armature current and speed of a 60 separately excited (3)
motor will be affected by halving armature voltage and field current with load
torque remaining constant.
Explain the speed control of separately excited DC motor using combined (7)
armature voltage and flux control method. Draw and explain the torque and
power capability curves.
Draw and explain the speed torque curves of a fan load and traction load (4)

Page 1 of 2