ALTERNATORS AND SYNCHRONOUS MACHINES 8

1. If the armature current is in phase with generated emf, the effect of armature reaction is
a) cross magnetizing
b) magnetizing
c) demagnetizing
d) none of these
ans. a

2. The value of voltage regulation as determined by synchronous impedance method is
a) greater than that found by actual loading
b) less than that found by actual loading
c) the same as that found by actual loading
d) none of these
ans. a

3. An alternator is connected to the bus bars and is supplying load. Its prime mover is suddenly shut down. The alternator will
a) continue to work as an alternator
b) continue to run as synchronous motor but direction of rotation will reverse
c) continue to run as synchronous motor and the direction of rotation will remain the same
d) none of the above
ans. c

4. Alternators generally use short pitch coils to remove harmonics from emf wave shape. As compared to full pitch coils, the short pitch coils need
a) more conductor material
b) the same amount of conductor material
c) less conductor material
d) none of the above
ans. c

5. The biggest size of the alternators used in India is
a) 200 MW
b) 350 MW
c) 500 MW
d) 1000 MW
ans. c

6.  In order to extract energy from an electrical system , the coupling magnetic field must react with
a) electrical system
b) mechanical system
c) both a and b
d) none of these
ans. a

7. Electromagnetic force or torque developed in any physical system tends to
a) increase the magnetic stored energy at constant flux
b) decrease the magnetic stored energy at constant current
c) decrease the reluctance
d) decrease the inductance
ans. c

8.  Reluctance motors are
a) doubly -excited
b) singly- excited
c) multiply-excited
d) none of these
ans. b

9. The doubly excited magnetic systems are
a) moving iron instruments
b) electromagnetic relays
c) solenoids
d) synchronous motors
ans. d

10. Reluctance torque in rotating machines is present when
a) air-gap is not uniform
b) reluctance seen by stator mmf is constant
c) reluctance seen by stator mmf varies
d) reluctance seen by rotor mmf is constant
ans. c