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**Question Paper Code : 13009**

**B.E/B. Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2012.**

**B.E Electrical and Electronics Engineering**

**Seventh Semester**

**Ee 2403/ee 73/10133 eee25-special electrical machines**

**(Regulation 2008)**

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**Part-a**

1)Give some potential applications of synchronous reluctance machine?

2)Write the various design parameters of a synchronous reluctance machine?

3)Calculate the stepping angle of a 3 phase,24 pole permanent magnet stepper motor?

4)Define torque constant of a stepper motor?

5)Why SR machines popular in adjustable speed drives?

6)What is the significance of rotor position sensor is essential for the operation of SR motors?

7)Compare and contrast conventional DC motors and PMBLDC motors?

8)A permanent magnet DC commutator motor has a stalling torque of 1 Nm.The stall current is 5 A.Compute the motors no-load speed if it is fed with 28 V DC supply?

9)Brief-up the advantages of load commutation in permnanent magnet synchronous synchronous motors?

10)What is maeant by self control?

**PART-B**

11. a) Describe in detail,the speed-torque and torque-angle characteristics of synchronous reluctance motors with phasor diagrams.(16)

(OR)

b)Explain the construction and working principle of synchronous reluctance motors in detail,with neat structural diagrams.(16)

12. a) i) Discuss in detail,about the construction ad working principle of variable reluctance stepper motors.(8)

ii) A single stack,3 phase variable reluctance motor has a step angle of 15 degrees.Find the number of stator and rotor poles.(8)

(OR)

b) i) What is the motor torque Tm required to accelerate an initial load of 2 x 10^-4 from 500 Hz to 1500 Hz in 50 ms.The frictional torque is 0.03Nm and step angle is 1.18 degrees.(8)

ii)Write a detailed technical note on the bipolar drives for stepper motors.(8)

13. a) i) Enumerate the various operating modes of SR motors with neat diagrams.(8)

ii) Discuss in detail,about the microprocessor based control of SR motor drives.(8)

(OR)

b) i) Explain the Torque-speed characteristics of switched reluctance motors(8)

ii) Derive the expressions for voltage and torque of SR machines.(8)

14. a) i) Describe the constructonal aspects of mechanical and electronic commutators of permanent magnet brushless DC motors.(8)

ii) A PMBLDC motor has a torque constant of 0.12 Nm/A referred to DC supply.Find the motor no-load speed when connected to 48 V DC supply.Find the stall current and stall torque if armature resistance is 0.15 ohms/phase and drop in controller resistance is 2 V.(8)

(OR)

b) i) A permanent magnet DC commutator motor has a no-load speed of 600 rpm when connected to a 120 DC supply.The armature resistance is 2.5 ohms and rotational and iron losses may be neglected.Determine the speed when the supply voltage is 60 V and the torque is 0.5 Nm.(8)

ii) Illustrate in detail,the operation of PMBLDC motor with 180 degrees magnet arcs and 120 degrees square-wave phase currents.(8)

15. a) i) Discuss the different rotor configurations of PM synchronous machines.(8)

ii) Derive the expression for the torque developed in a brushless permanent magnet synchrnous motors.

(OR)

b) Write a detailed technical note on the foolowing : (16)

i) Vector control of brushless permanent magnet synchrnous motors.

ii) Microprocessor based control.

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