# Design of Electrical Machines Questions and Answers – Design of Stator

This set of Design of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “Design of Stator”.

1. What type is the stator windings of the single phase induction motor?
a) hollow
b) cylindrical
c) concentric
d) rectangular

Explanation: The stator windings are also known as the running winding or the main winding. The type of stator winding used is concentric type

2. How many coils are present in the stator windings?
a) 2
b) 3
c) 2 or more
d) 3 or more

Explanation: The stator windings of single phase induction motors are concentric type. There are usually 3 or more coils per pole each having same or different number of turns.

3. How much of the total slots are used for the reduction of the mmf wave harmonics?
a) 60%
b) 65%
c) 70%
d) 80%

Explanation: 70% of the total slots are used for the reduction of the mmf wave harmonics. The remaining 30% are used for accommodating the starting windings.

4. How can the small single phase motor reduce the harmonics still much further?
a) removing the winding
b) insulating the winding

Explanation: 70% of the total slots are used for the reduction of the mmf wave harmonics. The mmf wave harmonics can be still further reduced by grading the winding.

5. What is the formula for the mean pitch factor?
a) mean pitch factor = pitch factor of each coil per pole group + turns in the coil / total number of turns
b) mean pitch factor = pitch factor of each coil per pole group / turns in the coil * total number of turns
c) mean pitch factor = pitch factor of each coil per pole group * turns in the coil * total number of turns
d) mean pitch factor = pitch factor of each coil per pole group * turns in the coil / total number of turns

Explanation: The pitch factor of each coil per pole group, turns in the coil and total number of turns are obtained. On substitution, it gives the mean pitch factor.
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6. What is the range of the winding factor for the usual windings distribution?
a) 0.70-0.80
b) 0.75-0.85
c) 0.70-0.85
d) 0.70-0.75

Explanation: The minimum value of the winding factor of the usual winding distribution is 0.75. The maximum value of the winding factor of the usual winding distribution is 0.85.

7. What is the formula of the maximum flux in the running winding?
a) maximum flux = flux * pole
b) maximum flux = flux/pole
c) maximum flux = flux / turns
d) maximum flux = flux * turns

Explanation: First the flux is calculated along with the number of poles used. On substituting the values the maximum flux value is obtained.

8. What is the value of the stator induced voltage with respect to the supply voltage?
a) stator induced voltage = 95% of supply voltage
b) stator induced voltage = 90% of supply voltage
c) stator induced voltage = 85% of supply voltage
d) stator induced voltage = 80% of supply voltage

Explanation: The winding factor is assumed to be 0.75-0.85 for the running winding. The stator induced voltage is 95% of the supply voltage.

9. How many design data are present in the design of the stator?
a) 6
b) 7
c) 8
d) 9

Explanation: There are 8 design data available in the design of the stator. The design data are running winding, number of turns In running winding, running winding conductors, number of stator slots, size of stator slot, stator teeth, stator core, length of mean turn.

10. What is the range of the current density for the open type motors split phase, capacitor and repulsion start motors?
a) 4-5 A per mm2
b) 3-4 A per mm2
c) 2-4 A per mm2
d) 1-4 A per mm2

Explanation: The minimum value of the current density for the open type motors split phase, capacitor and repulsion start motors is 3 A per mm2. The maximum value of the current density for the open type motors split phase, capacitor and repulsion start motors is 4 A per mm2.

11. What is the relation of the number of slots with the leakage reactance?
a) small number of slots, high leakage reactance
b) large number of slots, high leakage reactance
c) large number of slots, small leakage reactance
d) small number of slots, small leakage reactance

Explanation: The number of slots is indirectly proportional to the leakage reactance. The larger the number of slots, the lower will be the leakage reactance.

12. What is the formula for the area required for the insulated conductors?
a) area required for the insulated conductors = total number of conductors per slot * 0.785 / diameter of insulated conductor2
b) area required for the insulated conductors = total number of conductors per slot / 0.785 * diameter of insulated conductor2
c) area required for the insulated conductors = total number of conductors per slot * 0.785 * diameter of insulated conductor2
d) area required for the insulated conductors = 1/total number of conductors per slot * 0.785 * diameter of insulated conductor2

Explanation: The total number of conductors per slot and the diameter of insulated conductors are calculated. On substitution the area required for the insulated conductors are calculated.

13. The flux density of the high torque machines is 1.8 weber per m2.
a) true
b) false

Explanation: The flux density of the general purpose machine is 1.45 weber per m2. The flux density of the high torque machines is 1.8 weber per m2.

14. The flux density of the stator core should not exceed 1.3 weber per m2.
a) true
b) false

Explanation: The flux density of the stator core should not exceed 1.5 weber per m2. The range lies between 0.9 – 1.4 weber per m2.

15. What is the formula for the flux density in stator core?
a) flux density in stator core = maximum flux / length of the iron * depth of stator core
b) flux density in stator core = maximum flux * length of the iron * depth of stator core
c) flux density in stator core = maximum flux / 2 *length of the iron * depth of stator core
d) flux density in stator core = maximum flux * length of the iron / depth of stator core

Explanation: The maximum flux, length of iron and depth of stator core is calculated. On substitution it provides the flux density in stator core.

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