Electrical Machine - I (3140913) MCQs

MCQs of Principles of Electromechanical Energy Conversion

Showing 21 to 30 out of 34 Questions
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21.
In a doubly excited magnetic system of salient pole stator and rotor, the magnetic torque (Te) depends on (i) the instantaneous values of currents is and ir (ii) the angular rate of change of inductances (iii) the differential changes of current dis and dir (iv) only the instantaneous values of self inductance Which of the above statements are true?
(a) (i) & (iii)
(b) (i) & (ii)
(c) (iii) & (iv)
(d) (i) & (iv)
Answer:

Option (b)

22.
In a doubly excited magnetic system, the magnetic torques and forces act in such a direction as to tend to
(a) decrease the field energy at constant currents
(b) decrease the field co-energy at constant currents
(c) increase the field energy at constant currents
(d) none of the mentioned
Answer:

Option (c)

23.
In a doubly excited magnetic system of salient pole type stator and rotor, the reluctance torque is present only when _____________
(a) both stator and rotor currents are acting
(b) stator current is acting alone
(c) rotor current is acting alone
(d) any of the stator or rotor currents acting alone
Answer:

Option (d)

24.
In a doubly excited magnetic system of salient pole type stator and rotor, the reluctance torque is present only when _____________
(a) both stator and rotor currents are acting
(b) stator current is acting alone
(c) rotor current is acting alone
(d) any of the stator or rotor currents acting alone
Answer:

Option (d)

25.
Which component of torque in the following equation is called the electromagnetic torque of electromagnetic energy conversion device? Te=1/2 is2 dLs/dθr + 1/2 Ir2 dLr/dθr + Is Ir dMsr/dθr
(a) 1/2 is2 dLs/dθr
(b) 1/2 Ir2 dLr/dθr
(c) Is Ir dMsr/dθr
(d) all of the above
Answer:

Option (c)

26.
Which components of torque in the following equation are called the reluctance torque terms? Te=1/2 is2 dLs/dθr + 1/2 Ir2 dLr/dθr + Is Ir dMsr/dθr
(a) 1/2 is2 dLs/dθr and Is Ir dMsr/dθr
(b) 1/2 is2 dLs/dθr and 1/2 Ir2 dLr/dθr
(c) 1/2 Ir2 dLr/dθr and Is Ir dMsr/dθr
(d) 1/2 is2 dLs/dθr, 1/2 Ir2 dLr/dθr and Is Ir dMsr/dθr
Answer:

Option (b)

27.
Which of the following statements are true about electromagnetic torques and reluctance torques: (i) electromagnetic torque can exist only if both windings carry current. (ii) reluctance torque depends on the direction of current in stator or rotor windings. (iii) reluctance torque doesn’t depend on the direction of current in stator or rotor windings. (iv) electromagnetic torque depends on the direction of currents Is and Ir. (v) electromagnetic torque doesn’t depend on the direction of currents Is and Ir.
(a) (i), (ii) and(iii)
(b) (ii), (iii) and(v)
(c) (i), (iii) and (iv)
(d) (ii), (iii) and (iv)
Answer:

Option (c)

28.
Singly and doubly excited magnetic systems applications are respectively
(a) loud speakers and tachometers
(b) synchronous motors and moving iron instruments
(c) DC shunt machines and solenoids
(d) reluctance motors and synchronous motors
Answer:

Option (d)

29.
Electromagnetic torque in rotating electrical machinery is present when ________
(a) stator winding alone carries current
(b) rotor winding alone carries current
(c) air gap is uniform
(d) both stator and rotor windings carry current
Answer:

Option (d)

30.
All practical electromechanical energy conversion devices make use of the magnetic field rather than the electric field as the coupling medium.This is because
(a) electric field systems present insulation difficulties
(b) electric field systems have more dielectric loss than the magnetic loss, for the same power rating of the machine
(c) in electric field systems, for normal electric field strength, the stored energy density is high
(d) in magnetic field systems, for normal magnetic flux density, the stored energy density is high
Answer:

Option (d)

Showing 21 to 30 out of 34 Questions
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