# Design of Electrical Machines Questions and Answers – Construction of Hydro-Generators – 2

This set of Design of Electrical Machines Question Bank focuses on “Construction of Hydro-Generators – 2”.

1. What factor does the rotor body depends upon in the construction of hydro-generators?
a) speed
b) voltage
c) peripheral voltage
d) power

Explanation: In the hydro-generators the salient poles are attached to the rotor body. The type of rotor body used depends in general on the peripheral speed.

2. Which machine makes use of the forged steel construction?
a) low speed
b) high speed
c) very high speed
d) medium speed

Explanation: The forged steel construction is made use for the high speed machines. The earliest construction particularly at relatively low outputs consisted of a body and shaft extension made as single forging.

3. In what type of generator is the thick rolled steel discs made use of?
a) generators running at 400 rpm
b) generators running at 500 rpm
c) generators running at 600 rpm
d) generators running at 600 rpm and above

Explanation: Another type of rotor construction made use of in the hydro-generators is the thick rolled steel discs. It is made use for the generators running at 600 rpm and above.

4. What is the range of the length of the thick rolled sheets used in the rotor design of the hydro generators?
a) 130-180 mm
b) 120-180 mm
c) 150-180 mm
d) 160-190 mm

Explanation: The minimum value of the length of the thick rolled sheets used in the rotor design of the hydro-generators is 120 mm. The maximum value of the length of the thick rolled sheets used in the rotor design of the hydro-generators is 180 mm.

5. The laminations used in the rotor body design is 1.8 mm.
a) true
b) false

Explanation: The laminations used in the rotor body design is 1.8 mm. They are in the form of the overlapping segments tightly bolted.

6. For what peripheral speed of the machine is the segmental rim on fabricated spider used?
a) >120 m per s
b) <120 m per s
c) >130 m per s
d) <130 m per s

Explanation: The segmental rim on fabricated spider is used for the machines whose peripheral speed is upto 130 m per s. The advantage is it is easy to transport and assemble at site.

7. For what peripheral speed is the poles bolted to the yoke?
a) 20 m per s
b) 30 m per s
c) 25 m per s
d) 27 m per s

Explanation: The poles are clamped or fixed to the rim in different ways. In case of the generators the poles are bolted to the yoke when the peripheral speed is upto 25 m per s.

8. What is the range of the peripheral speeds in the water wheel generators?
a) 20 to 80 m per s
b) 20 to 50 m per s
c) 50 to 80 m per s
d) 30 to 70 m per s

Explanation: The minimum peripheral speed in the water wheel generators is 20 m per sec. The maximum peripheral speed in the water wheel generators is 80 m per sec.

9. The length of the mean turn of the winding is smallest with circular poles.
a) true
b) false

Explanation: The circular poles have a lot of advantages. The length of the mean turn of the winding is smallest with circular poles and therefore cost is reduced. The copper losses are also less.

10. Why are damper windings used in the construction of hydro-generators?
a) to control losses
b) to increases efficiency
c) to reduce the oscillations
d) to reduces voltage surges

Explanation: The damper windings are generally used in the construction of hydro-generators. It is generally used to reduce the oscillations in the generator.

11. By how much is the rotor and the turbine runner and the hydraulic thrust requirements more than the dead weight of rotating masses?
a) thrice
b) twice
c) by 4 times
d) by 8 times

Explanation: In case of the vertical shaft generators special features have to be incorporated in the bearing set up. This is because the rotor and the turbine runner and the hydraulic thrust requirements is twice more than the dead weight of rotating masses.

12. How are the bearing cooled in the construction?
a) natural cooling
b) forced cooling
c) air cooling
d) oil cooling

Explanation: Oil is the material which is used for the cooling of the bearings. It is being supplied to the bearings by the pump.

13. By how many minutes is the complete energy of the rotating parts and the machine is brought to rest?
a) 2 minutes
b) 1 minute
c) 3 minutes
d) 4 minutes

Explanation: The brakes are so designed such that the complete energy of the rotating parts and the machine is brought to rest. It is brought to rest by 3 minutes.

14. What material is used to make the material of the pads of the brakes?
d) pads using the asbestos interlaced with metal wires.

Explanation: The brakes are made to stop the machines immediately to protect the bearings. The brakes have pads using the asbestos interlaced with metal wires.

15. Why are the slip rings made use of?
a) they are used to provide excitation to field windings
b) they are used to provide excitation to the armature windings
c) they are used to reduce the heating effects
d) they are used to reduce the losses

Explanation: The slip rings are the last construction material made use of in the hydro-generators construction. They are used to provide excitation to the field windings.

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

To practice Design of Electrical Machines Question Bank, here is complete set of 1000+ Multiple Choice Questions and Answers.