IED (Imp Questions)

INRODUCTION TO ELECTRIC DRIVES

Assignment 5

1. Describe static kramer drive and show that the steady state torque is not influenced by

whether a transformer is used or not. Derive appropriate expressions to obtain torque-speed

characteristics of ststic kramer drive.

2. Enumerate the various methods od speed control of 3-phase induction motor ehem fed through

semiconductor devices.

3. Descibe the regenerative braking of a chopper fed seperately excited DC motor. Illustrate

answer with circuit diagram and relevant waveforms.

4. The speed of a seperately-excited dc motor is controlled through 1-phase half wave controlled

converter from 230V mains. The motor armature resistance is 0.5 ohms and motor constant

is K = 0.4 V-s/rad. For load torque of 20Nm at 1500 rpm and for constant armature current,

calculate:

i) Firing angle of the coverter

ii) Rms value of thyristor current

iii) i\p power factor of motor

5. Explain the cocept of step down cyclocoverter. Enumerate the advantages and applications of

cycloconverter.

6. Give the differences between 180 and 120° modes of 3-phase with relevant waveforms of phase

and line voltages.

7. Explain three-phase half controlled full wave rectifier with desired waveforms.

8. Derive the expression of a 1-hase full wave bridge rectifier fully controlled for R-L-E load.

9. An armature (RLE load) of a seperately dc motor is fed from 1-phase full wave fully controlles

covereter. The supply ac voltage V= 220V, Ra = 0.06 ohms, La =0.085 mH, Ia=150A, speed = 875

rpm, Va = 200V. Find the output voltage and α for a rated load when :

 i)E = 160V (speed = 733 rpm, 1st quadrant)

 ii)E = -190V (speed = -500 rpm, 4th quadrant )

10. What are ac drives? Give merits and demerits of ac drives with respect to dc drives.

11. Define speed control od induction motors. Define method of resistance control.

12. Explain basi machine equations. Define DC motor speed control .

13. Explain single phase full wave bridge converter. Also explain three phase bridge inverter.

14. Draw the circuit diagram and explain the working of slip power recovery system using ststic

Scherbius drive and also draw the torque-speed characteristics.

15. What is the basic principle of operation of an induction motor, Explain it with reference to

equivalent circuit.

16. What is Jones chopper? Explain with its voltage and current waveforms.