Ac machine

Ac machine  , some  important mcq  

( 2018 EVEN,  polytechnic  5th sem)

1. The short-circuit characteristics of      an alternator is

      (a) Always linear

      (b) Always non-linea

     (0) Either (a) or (b)

     (d) None of the above 

2. 6-pole, 50 HZ 3-phase induction motor       is running at 950 rpm and has rotor           Cu-loss of 5 kw. Its rotor input is

    (a) 100 kw

       

     (b) 10 kw

    (c) 95 kw 

     (d) 5.3 kw

3. Alternator can be excited by

(a) A.C.

(b) None of these

(c) D.C.

(d) Both (a) and (b)

4. No. of slips-ring in a 3-phase                       synchronous motor will be

    (a) 0

    (b) 1

    (c) 2

     (d) 4

5.The power factor of an alternator is          determined by its 

   (b) Load

   (b)  Prime mover

    (c) load 

    (d) excitation 

6. A4-pole, 1200 rpm alternator will          generate emf at  

(a) 50 Hz
 (b) 40 Hz
 (c)  60 Hz
(d) 25 Hz

7. In an alternator the armature flux       helps the main field flux when the      load power factor is

 (a) Unity

 (b) zero lagging

 (c) 0.8 lagging 

(d) Zero leading

8. In an alternator damper winding are       used to

 (a) Reduce eddy current loss

(b) Prevent hunting

(c) Reduce armature reaction 

(d) None of these

9.The maximum possible speed at                 which  alternator can be driven to             generate 60 Hz and 4000 volts is

(a) 3600 rpm

(b) 3000 rpm

(c) 4000 rpm 

(d) 1500 rpm

10. In a 3-phase synchronous motor, the       magnitude of field  flux 

(a) Remains constant at all loads 

(b) Varies with load 

(c) Varies with speed 

(d) Varies with power factor

 11.When a synchronous motor is                    running at synchronous speed, the            damper winding produces 

 (a) Damping torque

 (6) Eddy current torque

(c) Torque adding the developed torque

(d) No torque

12. A 3-phase, 4 pole , 50 Hz induction              motor is    running at 1425 rpm                    while supplying full load. Its slip  is

      (a) 5%

       (b) 4% 

       (c) 3%

      (d) 10%

13. Rotating magnetic field is produced           in 

(a) 3 phase  induction  motor 

(b) dc series  motor 

(c) Ac series  motor 

(d) none of these

15 .The power factor of an induction               motor at full load  is around 

(a) Unity 

(b) 0.85 lagging

(c) 0.5 leading 

(d) 0.85 Leading 

15.A ceiling fan uses

(c) Cupacitor start motor

 (d ) Capacitor start capacitor run motor

(d) None of these

16. Stator of an induction motor is made         of 

(a) Carbon 

(b) Wood

(c) Silicon steel laminations

 (d) None of these 

17. The motor used in electric toys

(a) Capacitor start motor

 (c) Shaded pole motor

(c) shaded pole motor 

(d)  none of above 

18 .The short circuit characteristic of an        alternator is

(a) always  linear 

(b) Always  non linear 

(c) Either  A ans B 

(d) none  of  the  above 

19. Alternator are rated  in

(a) MW

(b) KVAR

(c) KWH 

(d)KWA

20.No of slips rings  in a 3 phase    synchronous  motor  will be 

(a) 0 

(b) 1 

(c) 2

(d) 4