Electrical Machines Questions and Answers_pag346

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b) C/2 
c) 2C/P 
d) C/2P 
View Answer 
Answer: c 
Explanation: backward pitch for an equalizer ring = number of coils/pole pairs = C/P/2=2C/P. 
12. With a P-pole DC machine with armature current Ia, the current per brush arm for a lap 
connected windings is 
a) Ia/P 
b) Ia/2P 
c) 2Ia/P 
d) Ia/4P 
View Answer 
Answer: c 
Explanation: Current per brush (lap winding) = total armature current/Number of pole pairs. 
13. For a given dc machine it is advised to use the dummy windings for a stable operation. But if 
it has be replaced as it unused component in the machine, then we must 
a) S/P/2 should not be an integer 
b) S/P/2 should be integer 
c) S/P should be integer 
d) S/P should not be an integer 
View Answer 
Answer: a 
Explanation: If slots per pole pair is not integer than all the winding will be completed without 
adding any dummy coil. 
14. While doing regular checks on the dc machine with the lap connected winding, it is reported 
to have ammeter fluctuations, this can be due to 
a) different air gaps under poles 
b) variable reluctances in the core 
c) irregular design deformations 
d) all of the mentioned 
View Answer 
Answer: d 
Explanation: In a lap winding configuration, if the machine as air gap variations due to the 
design aspects, it will give circulating current in the windings. 
15. A 6-pole lap wound DC generator has a developed power of P watts and brush voltage of E 
volts. 
Three adjacent brushes of the machine had been found worn out and got open circuited. 
If the machine is operated with the remaining brushes, voltage and power that could be 
obtained from the machine are 
a) E,P 
b) E,2P/3 
c) E/P,2P/3