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

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

1. What is the consideration for the determination of the diameter of shaft?
a) stiffness
b) voltage
c) current
d) rigidity

Explanation: The main aspect for the design of the diameter of the shaft is the stiffness. The diameter of the shaft depends on the stiffness of the machine.

2. What is the meaning of stiffness?
a) ability to transmit the power
b) ability to withstand the weight of the rotor
c) ability to withstand unbalanced magnetic pull
d) ability to withstand the weight of rotor and unbalanced magnetic pull

Explanation: The diameter of shaft for an electrical machine is determined by considerations of stiffness. The stiffness is the ability to withstand the weight of rotor and unbalanced magnetic pull.

3. What should be the first property of the shaft design?
a) the shaft design should be such that the shaft must have enough corrosion resistance
b) the shaft design should be such that the shaft must have enough mechanical strength
c) the shaft design should be such that the shaft has enough tensile strength
d) the shaft design should be able to withstand the voltage fluctuations

Explanation: The shaft design should be such that the shaft must have enough mechanical strength. The strength should be such that it should withstand all loads without causing much residual strain.

4. What is the second property of the shaft design?
a) the shaft design should be such that it has high rigidity
b) the shaft design should be such that it should have high tensile strength
c) the shaft design should be such that it should have high corrosion resistance
d) the shaft design should be such that it should withstand voltage fluctuations

Explanation: The second property of the shaft design such that it should have high rigidity. The rigidity should be such that the deflection of shaft under operation of machine does not reach such a dangerous value as to cause the rotor to touch the stator.

5. The critical speeds of rotation should be different from running speed of machine.
a) true
b) false

Explanation: The critical speed relation is the third property of the shaft design. The critical speeds of rotation should be different from the running speed of the machine.
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6. What is the formula of the diameter of the shaft?
a) diameter of the shaft = 5.5 + (output in watt/rps)1/3 mm
b) diameter of the shaft = 5.5 – (output in watt/rps)1/3 mm
c) diameter of the shaft = 5.5 * (output in watt/rps)1/3 mm
d) diameter of the shaft = 5.5 / (output in watt/rps)1/3 mm

Explanation: The output is first calculated from the operation of the machine. Next, the tachogenerator is used to calculate the speed of the machine and on the substitution of the values gives the diameter of the shaft.

7. What is the relation of the diameter of the shaft in the bearings to the diameter under the armature?
a) diameter of the shaft is very much greater than the diameter under the armature
b) diameter of the shaft is greater than the diameter under the armature
c) diameter of the shaft is equal to the diameter under the armature
d) diameter of the shaft is lesser than the diameter under the armature

Explanation: There are certain rules in the design of the shaft. The diameter of the shaft in the bearings is less than the diameter under the armature.

8. What happens when the diameter under armature is 150 mm or above?
a) diameter of the shaft in bearing is 100 mm smaller than the maximum diameter
b) diameter of the shaft in bearing is 90 mm smaller than the maximum diameter
c) diameter of the shaft in bearing is 70 mm smaller than the maximum diameter
d) diameter of the shaft in bearing is 50 mm smaller than the maximum diameter

Explanation: The diameter of the shaft in the bearings is less than the diameter under the armature. The diameter of the shaft in bearing is 50 mm smaller than the maximum diameter.

9. What happens in the case of the small shafts?
a) the diameter in the bearings should be about 1/3 of the maximum diameter
b) the diameter in the bearing should be about 2/3 of the maximum diameter
c) the diameter in the bearing should be about 2/5 of the maximum diameter
d) the diameter in the bearing should be about 1/5 of the maximum diameter

Explanation: The diameter of the shaft in the bearings is less than the diameter under the armature. The diameter in the bearing should be 2/3 of the maximum diameter.

Sanfoundry Global Education & Learning Series – Design of Electrical Machines.

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