1. Which are the important criteria related to the power ratings of the machine?
a) Heat should be prevented from generation
b) Heat should be dissipated through power ventilation, irrespective of the time
c) Heat should be prevented through power ventilation within a short time period
d) Heat should be converted to some useful form
Explanation: Due to the components present in the machine, I2R losses occur in the machine. Due to this, heat is produced, and proper thermal ventilation should be provided to prevent the machine from breakdown.
2. What is the concept of thermal loading?
a) Output power is indirectly proportional to the temperature rise
b) Output power is indirectly proportional to the square of temperature rise
c) Output power is directly proportional to the temperature rise
d) Output power is directly proportional to the square of temperature rise
Explanation: Thermal loading is nothing, but the increase of the output power with respect to the temperature rise. It can lead to the power rating levels being crossed.
3. What is the ideal condition for thermal dissipation?
a) Heat generated > Heat Dissipated
b) Heat generated < Heat Dissipated
c) Heat generated = Heat Dissipated
d) Heat generated = 0
Explanation: For ideal thermal dissipation, the heat dissipated should be equal to the heat generated. In that case, there will be very less power loss and high efficiency
4. What is the main objective of power ratings of machines?
a) helps in building a suitable thermal model of machines
b) helps in building a suitable physical model of machines
c) helps in classifying the machines into different types
d) helps to improve the machine efficiency
Explanation: The power ratings, mainly help in building the thermal model. It helps in reducing the heat losses and helps in bringing out a smooth and efficient operation of the machines.
5. Power ratings help in classifying machines to different classes of duties.
a) true
b) false
Explanation: The classification of the machines into different classes of duties depends on the power ratings. The ratings also helps in identifying the different types of machines available under different classes.
6. How many type of armature windings are present in the DC machine armature?
a) 2
b) 3
c) 4
d) 5
Explanation: There are basically two types of armature windings present. They are known as lap winding and wave winding.
7. Which factor determines the difference between the types of armature windings?
a) brush connection
b) slip ring connection
c) commutator connection
d) pole connection
Explanation: The armature windings are all connected to the commutator in the case of DC machines. Commutator is nothing but device which converts dc voltage to ac voltage.
8. What is the meaning of pole pitch?
a) type of armature slot
b) number of armature slots/pole
c) number of poles/armature slot
d) number of poles/number of armature slots
Explanation: Pole pitch is the concept which is used in the armature slot design. It is nothing but the ratio between the number of armature slots present to the number of poles used in the machine design.
9. A 4 pole DC machine has 36 number of armature conductors. What is the pole pitch?
a) 9
b) 1/9
c) 92
d) 1/92
Explanation: Pole pitch = Number of armature slots/pole
Pole Pitch = 36/4 = 9.
10. The choosing of the slot values for armature depends on the type of windings.
a) true
b) false
Explanation: The slot values are chosen based on the type of windings. If wave winding is used, then multiples of pole pair is chosen as slot values and if lap windings are used the slot values are continuous and not multiples of pole pair.