# Design of Electrical Machines Questions and Answers – Construction of Turbo-Alternators

This set of Design of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “Construction of Turbo-Alternators”.

1. How many factors does the construction of the turbo alternators depend upon?
a) 2
b) 4
c) 3
d) 6

Explanation: There are 3 factors which decide the construction of the turbo-alternators. They are i) stator core ii) stator winding iii) rotor.

2. How many poles does the turbo-alternators have and what is the speed of the turbo alternators?
a) 4 poles, 3000 rpm
b) 3 poles, 6000 rpm
c) 2 poles, 5000 rpm
d) 2 poles, 3000 rpm

Explanation: The turbo-alternators are made up of 2 poles. The speed with which the turbo alternators operate are 3000 rpm.

3. What is the relation of the lengths and diameters with the turbo-alternators?
a) long length, long diameters
b) long length, short diameters
c) short lengths, short diameters
d) short lengths, long diameters

Explanation: The turbo-alternators are characterized by the long lengths. The turbo-alternators are also characterized by short diameters.

4. What is the core length and the shaft length of a 500 MW turbo alternator?
a) 5 m, 12 m
b) 6 m, 15 m
c) 3 m, 10 m
d) 4 m, 13 m

Explanation: The core length of a 500 MW turbo alternator is 5 m. The shaft length of the 500 MW turbo alternator is 12 m.

5. What is the outer diameter of the stator core and outer casing of 500 MW turbo alternator?
a) 5 m, 2 m
b) 6 m, 5 m
c) 3 m, 4 m
d) 4 m, 7 m

Explanation: For a 500 MW turbo alternator the outer diameter of the stator core is 3 m. The diameter of the outer casing is 4 m.

6. What type of lamination is used for the stator core of the turbo alternators?
a) stepped
b) smooth
c) interleaved
d) segmental

Explanation: The stator core is made up of segmental laminations. The grain oriented steel laminations are another type of stator laminations made use of.

7. What is the advantage of the grain oriented steel laminations?
a) it lowers the iron loss
b) it lowers the core loss
c) it lowers the heating effects
d) it lowers the harmonics

Explanation: The grain oriented steel laminations are also one type of laminations used for the stator core. They result in the lowering of the core loss.

8. What is the pulsational force produced for 500 MW machine?
a) 70 kN per m
b) 60 kN per m
c) 80 kN per m
d) 90 kN per m

Explanation: The generator designed with low voltage gives high currents which produce high pulsational forces. The pulsational forces can be as high as 80 kN per m.

9. What is the use of the laminated and transposed conductors in turbo alternators?
a) to decrease the harmonics
b) to decrease the heating effects
c) to decrease the iron and core loss
d) to decrease the eddy current loss

Explanation: The presence of large currents requires the use of multi circuit windings. The use of the laminated and transposed conductors in turbo alternators is to reduce the eddy current loss.

10. What is the voltage range for large turbo-alternators?
a) 15-20 kV
b) 18-23 kV
c) 20-23 kV
d) 20-25 kV

Explanation: The generation voltage normally used are 15 kV for 100-200 MW machines. The voltage range for the large turbo-alternators are 20-25 kV.

11. The overhang has to be highly reinforced in turbo alternators.
a) true
b) false

Explanation: The overhang has to be highly reinforced in turbo alternators. The overhang is distributed over a large number of sections which eliminates the concentration of conductors in the overhang.

12. What is the use of the slot in the rotor?
a) for inserting the field windings
b) for inserting the armature windings
c) for securing the field windings
d) for inserting and securing the field windings

Explanation: The rotors slots are used for inserting the field windings. The rotor slots are also used for securing the field windings also.

13. How many types are the rotor slots distinguished into?
a) 2
b) 3
c) 4
d) 5

Explanation: There are 2 types of rotor slots in the turbo-alternators. They are i) radial sort ii) parallel slot rotors.

14. The rotor is slotted for one-third of its periphery.
a) true
b) false

Explanation: The rotor is slotted for only two-thirds of its periphery. It is because to reduce the flux pulsations and the cost factors.

15. What is the mechanical strength of the end bells used?
a) 1120 MN per m2
b) 1130 MN per m2
c) 1150 MN per m2
d) 1140 MN per m2

Explanation: The end bells are made of a non-magnetic austenitic steel in order to reduce the leakage flux. The end bells have high mechanical strength of about 1150 MN per m2.

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

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