Electrical Machines Mock Test 1

10%

Question 1 of 10

1. Which of the following are examples of doubly-excited magnetic systems?

Loudspeakers and Tachometers

All of the mentioned

D.C Shunt Machines

Synchronous Machines

Question 1 of 10

Question 2 of 10

2. The basic torque and EMF expression of rotating electrical machines are ____________

none of the mentioned

applicable to DC machines only

applicable to both AC and DC machines

applicable to AC machines only

Question 2 of 10

Question 3 of 10

3. The electromagnetic torque developed in any physical system, and with magnetic saturation neglected, acts in such a direction as to tend to ____________

increase the reluctance and decrease the inductance

decrease the reluctance and increase the inductance

decrease both the reluctance and inductance

increase both the reluctance and inductance

Question 3 of 10

Question 4 of 10

4. If the salient pole rotor in a single phase reluctance motor is replaced by a cylindrical rotor, then Which of the following statements are true?

(i) reluctance offered to stator flux remains constant for all rotor positions
(ii) no reluctance torque will be developed
(iii) reluctance torque will be developed
(iv) reluctance offered to stator flux changes for all rotor positions

(i), (iv)

(ii), (iii)

(i), (ii)

(iii), (iv)

Question 4 of 10

Question 5 of 10

5. Magnetic stored energy density for iron is given by ______

1/2 ∅² Rl

1/2 B²/μ

1/2 B² μ

1/2 B/μ

Question 5 of 10

Question 6 of 10

6. Why is the air gap between stator and rotor should be kept as small as mechanically possible in induction motor?

as it leads to better operating power factor of the induction motor

reduce the eddy current losses

both, to reduce leakage flux between stator and rotor, and also for better operating power factor

to reduce the leakage flux between stator and rotor

Question 6 of 10

Question 7 of 10

7. The developed electromagnetic force and/or torque in electromechanical energy conversion systems, acts in a direction that tends to ___________

(i) increase the co-energy at constant flux
(ii) increase the co-energy at constant mmf
(iii) decrease the stored energy at constant mmf
(iv) decrease the stored energy at constant flux

Which of the above statements are correct?

(i), (iii)

(ii), (iii)

(i), (iv)

(ii), (iv)

Question 7 of 10

Question 8 of 10

8. One turn consists of _____________

two coil sides

four coil sides

two conductors

four conductors

Question 8 of 10

Question 9 of 10

9. In a 4 pole machine, what is the flux per pole produced, if the armature length is l and radius is r and B_p is peak value of sinusoidal flux?

4B_plr

2B_plr

B_plr

B_plr/2

Question 9 of 10

Question 10 of 10

10. What is the amplitude of rotating MMF produced as a result of m-phase currents flowing in m-phase windings? (where F_m is maximum MMF in any one phase, when current is maximum in that phase.)

(2/m)F_m

(m/2)F_m

mF_m

F_m

Question 10 of 10