Electrical Machines Questions and Answers_pag165

Text Material Preview

Answer: a 
Explanation: All the listed factors are disadvantages for using a synchronous motor. 
5. The condition which allows the torques to be taken care for choosing a synchronous motor 
is/are 
a) starting torque 
b) pull-in torque 
c) pull-out torque 
d) all of the mentioned 
View Answer 
Answer: d 
Explanation: All the performance torques are needed to know before using any synchronous 
motor. 
6. A synchronous machine with its field winding on stator and polyphase armature winding on 
rotor. At steady state, its air gap field is 
a) stationary w.r.t. stator 
b) rotating at double the speed Ns w.r.t. rotor 
c) rotating in direction opposite to rotor 
d) all of the mentioned 
View Answer 
Answer: d 
Explanation: All are correct. 
7. A synchronous machine with its field winding on rotor and polyphase armature winding on 
stator. At steady state running condition, its air gap field is 
a) stationary w.r.t. stator 
b) rotating at double the Ns w.r.t. rotor 
c) rotating at -Ns w.r.t. rotor 
d) stationary w.r.t. rotor. 
View Answer 
Answer: d 
Explanation: As the field is on rotor itself, the sir gap will be stationary w.r.t. rotor. 
8. Choose the appropriate 
The synchronous generators used in the thermal power stations have 
(i) cylindrical rotor 
(ii)slip rings and brushes 
(iii)laminated rotor 
(iv)stator slots in the multiple of 6 
(v)salient rotor 
a) (i),(ii),(iv) 
b) (ii),(iii),(v) 
c) (i),(iii) 
d) (ii),(iii),(iv),(v) 
View Answer 
Answer: a