Which of the following in an application of D.C. motors?

Related Mcqs:

1. Which of the following materials is used in the manufacture of resistance grids to be used in the starters of large motors ?

   A. Copper
   B. Aluminium
   C. Steel
   D. Cast-iron

2. Which of the following problem arises in D.C. motors which are fed from thyristor bridge circuits ?

   A. Increased I R losses
   B. Increased core losses
   C. Poor commutation
   D. Change in motor parameters
   E. All of the above

3. In induction motors, the length of air gap in kept as small as mechanically possible is order to have____________?

   A. low power factor
   B. high power factor
   C. high over load capacity
   D. any of the above

4. In self cooled motors the cooling time constant is about ___________ than the heating time constant because cooling conditions are worse at standstill?

   A. 2 to 3 times greater
   B. 3 to 4 times greater
   C. 4 to 5 times greater
   D. none of the above

5. The action of electromagnetic machines can be related to which of the following basic principles __________?

   A. Induction
   B. Interaction
   C. Alignment
   D. All of the above

6. Which of the following is an advantage of hydrogen cooling ?

   A. Increase in efficiency
   B. Increase in ratings
   C. Increase in life
   D. Smaller size of coolers
   E. All of the above

7. On which of the following variables heat convected depends ?

   A. Power density
   B. Temperature difference between heated surface and coolant
   C. Thermal resistivity, density, specific heat
   D. Gravitational constant
   E. All of the above

8. By which of the following methods motor rating for variable load drives can be determined ?

   A. Method of average losses
   B. Equivalent current method
   C. Equivalent torque method
   D. Equivalent power method
   E. All of the above

9. Which of the following methods is most accurate ?

   A. Equivalent current method
   B. Equivalent power method
   C. Equivalent torque method
   D. Method of average losses

10. Which of the following is the basic consideration in the design of insulation ?

    A. Electrical considerations
    B. Mechanical considerations
    C. Thermal considerations
    D. All of the above