APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
SECOND SEMESTER M.TECH DEGREE EXAMINATION, MAY 201 8
Electrical and Electronics Engineering

(Electrical Machines, Power Control and Drives)
OIEE6302 Electric Drives

Max. Marks : 60 Duration: 3 Hours

Part A

|. a) Explain steady state stability of electrical drives. (5 marks)
0) A 220V, 875rpm, 150A separately excited dc motor has an armature resistance of
0.060hm. it is fed from a single phase fully controlled rectifier with an ac source voltage

of 220V, 50 Hz.

Assuming continuous conduction, calculate

(i) firing angle for rated motor torque and 750rpm

(ii) firing angle for twice rated motor torque and -500 rpm.

(iii) motor speed for (1=160°(4 marks)

2. a) A motor drives two loads and has an inertia of 0.2 kg-m* and runs at a constant speed
of 1000 rpm. One load has rotational motion. It is coupled to the motor through a
reduction gear with a—O.2 and efficiency of 80%. The load has a moment of inertia of 5
(8-77 300 a torque of 5Nm. Other load has translational motion and consists of 100 kg
weight to be lifted up at a uniform speed of | .5 m/s. coupling between this load and the
motor has an efficiency of 90%. Determine equivalent inertia referred to the motor shaft
and power developed by the motor.

(6 marks)
b) What are the classifications of load torque? Draw the speed-torque characteristics of any

three loads. (3 marks)

3. Explain the four quadrant operation of a separately excited dc motor using dual converter in
circulating current mode. (9 marks)

Part B

4. a) Explain the closed loop operation of stator voltage control of induction motor drives
with

necessary diagrams. (6 marks)