1. What happens to the weight of copper in both armature and field windings when the number of poles increase?
a) weight of copper in armature winding decreases and weight of copper in field winding increases
b) weight of copper in armature winding increases and weight of copper in field winding decreases
c) weight of copper in armature winding and field winding decreases
d) weight of copper in armature winding and field winding increases
Explanation: The weight of copper is indirectly proportional to the number of poles. As the number of poles increases, the weight of the copper decreases
2. What happens to the length of the commutators with the increase in number of poles?
a) The length of commutators are increased
b) The length of commutators are decreased
c) The length of commutators are stable
d) The length of commutators are higher
Explanation: The area of the brushes decreases if the number of poles are being increased. As the area of the brushes are decreased, the length of the commutators also decrease.
3. What happens to the labor charges when there is an increase in number of poles?
a) labor charges are reduced
b) labor charges are increased
c) labor charges are fixed always
d) labor charges vary
Explanation: With increase in the number of poles, the armature windings increase, and more work increases to insulate. The commutator segments also increase, and the work increases
4. What is the effect of the distortion of field form with respect to the small number of poles?
a) small number of poles cause no distortions
b) small number of poles clears all distortions
c) small number of poles reduces distortions
d) small number of poles increases distortions
Explanation: When there is small number of poles, that time the armature mmf per pole increases. As the armature mmf increases, it results in increase of distortion.
5. Large number of poles lead to large flashover between brushes.
a) True
b) False
Explanation: The number of brushes is equal to number of poles. For the same diameter of the commutator, the distance between the adjacent brush arms decreases and this increases the possibility of flashover
6. What is the dependency of the cost of the armature and field windings with respect to large number of poles?
a) high cost for armature windings, low cost for field windings
b) high cost for armature windings, high cost for field windings
c) low cost for armature windings, high cost for field windings
d) low cost for armature windings, low cost for field windings
Explanation: With large number of poles the armature and the field windings reduce in number. Thus the cost of the field and armature windings also decrease.
7. Lower values of frequency are used for small machines.
a) True
b) False
Explanation: Lower values of frequency are actually used for the large machines. Also, higher values of frequency are actually used for small machines
8. What is the range of the current per parallel path for the choice of number of poles?
a) limited to 100 A
b) limited to 150 A
c) limited to 200 A
d) limited to 250 A
Explanation: The current per parallel path should be limited to maximum of 200 A. If the limit gets exceeded then there occurs damage to the machine
9. What should be the range of the current per brush arm?
a) limited to 400 A
b) limited to 200 A
c) limited to 100 A
d) limited to 300 A
Explanation: The current per brush arm should be limited to maximum of 400 A. If the limit gets exceeded then there occurs damage to the machine
10. What should be the armature mmf per pole for output over 1500 kW?
a) 5000 A
b) 5000-7500 A
c) 7500-10000 A
d) upto 12500
Explanation: 5000 A is for output of about 100 kW. 5000 to 7500 A for output voltage of 100 to 500 kW. 7500 to 10000 A is for the output of 500 to 1500 kW