11. The field system of an alternator is usually excited at
- 250/250 V dc
- 110/220 V ac
- 3-phase 50 Hz 400 V
- 230 V ac
12. The open slots are more commonly used in the stator of a synchronous machine as
- the inductance of the winding is less
- they permit the placement of form wound and insulated coils giving least expensive and more satisfactory
- both (1) and (2)
- none of these
13. The slip rings employed in a 3-phase synchronous machine are insulated for
- output rated voltage
- low voltage
- very low voltage
- very high voltage
14. Squirrel cage bars placed in the rotor pole faces of an alternator help reducing hunting
- above synchronous speed only
- below synchronous speed only
- above and below synchronous speeds both
- none of the above
15. Hydro-generators are generally employed to run at _______ rpm.
- 500
- 1000
- 1500
- 3000
16. In case of turbo alternators, rotor is made of
- forged steel
- cast iron
- stainless steel
- laminated silicon steel
17. The salient pole rotors have
- a large number of projecting poles carrying the field coils
- thick steel laminations riveted together and fixed to the rotor by a dove-tail joint
- pole faces usually provided with slots for damper windings
- all the above
18. In salient pole field structure, the pole shoes cover about _____ of pole pitch.
- one-third
- one half
- two-third
- whole
19. Large diameter salient pole rotors have shorter axial length because
- it occupies much less space
- it saves lot of copper in stator winding
- it reduces weight of the rotor
- number of conductors held in large circumference of rotor is very large and so they need not be long
20. The number of poles on turbo-alternator is usually
- 2
- 4
- 6
- 8