# Sathyabama University Question Papers

# Special Electrical Machines BE Fifth Sem

PART – A (10 x 2 = 20)

Answer All the Questions

1. State the principle of vernier motor.

2. Define reluctance torque.

3. State any two advantages of variable reluctance motor.

4. Draw the block diagram of stepper motor.

5. List the two differences between a stepper motor and switched

reluctance motor.

6. Write the torque equation of switched reluctance motor.

7. Name the position sensors that are used for PMBLDC motor.

8. Why the PMBLDC motor is called electronically commutated

motor?

9. How a permanent magnet synchronous motor is started?

10. What is meant by field oriented control of PM synchronous

motor?

PART – B (5 x 12 = 60)

Answer All the Questions

11. Draw and discuss the torque – speed characteristics of single

phase synchronous reluctance motor.

(or)

12. Explain in detail the construction and principle of operation of

vernier motor.

13. A stepper motor has a step angle of 2.5°. Find resolution, number

of steps required for the shaft to make 25 revolutions and shaft

speed if stepping frequency is 3600 pulse/sec.

(or)

14. A single stack 3-phase variable reluctance motor has a stepping

angle of 15°. Find the number of its stator and rotor poles.

15. A switched reluctance motor with six stator poles and four rotor

poles has stator pole arc of 30° and rotor pole arc of 32°. The

aligned inductance is 10.7 mH and unaligned inductance is 1.5

mH. Saturation can be neglected. Calculate the instantaneous

torque when the rotor is 30° before the aligned position and the

phase current is 7 A.

(or)

16. Derive the torque equation and develop the mechanical

characteristics of switched reluctance motor.

17. A 3-phase four pole brushless PM motor has 36 stator slots. Each

phase winding is made up of three coils per pole with 20 turns

per coil. The coil span is seven slots. If the fundamental

component of magnet flux is 1.8 mwb, calculate the open circuit

phase emf Eg at 3000 rpm.

(or)

18. Derive an expression for permeance coefficient (PC) for

PMBLDC motor interms of magnet permeance Pms, rotor leakage

per phase Prl and air gap reluctance Rg.

19. Explain the principle of operation of a sine wave PM

synchronous machine. Draw its phasor diagram and derive its

torque equation.

(or)

20. Discuss PMBLDC and PM synchronous motor with respect to

torque / ampere and kVA of converter / kW of power to motor

for 4-pole, 3-phase motor system.