Electrical Machines Questions and Answers_pag89

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Answer: b 
Explanation: Interpoles do not reduce the flux across the windings, hence the speed does not 
rise above base speed. 
14. A 200 V dc motor has external resistances of Ra and Rf in armature and field circuits 
respectively. The starting current is reduced when 
a) Ra is maximum and Rf minimum 
b) Rf is maximum and Ra minimum 
c) Ra is minimum and Rf minimum 
d) Ra is maximum and Rf maximum 
View Answer 
Answer: a 
Explanation: When Ra is maximum and Rf minimum then the current to the armature is 
reduced. And hence the sparkings are reduced while starting. 
15. A d.c. generator has been provided tappings on the armature winding at intervals of 120 
degrees from the side of commutator. The connection will be 
a) delta connected alternator 
b) star connected alternator 
c) star connected induction motor 
d) any of the mentioned 
View Answer 
Answer: a 
Explanation: Dc generator if has displaced by 120 degrees physically then it will be act as ac 
machine. 
9. Questions & Answers on DC Generators 
This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on 
“Operating Characteristics of DC Generators”. 
1. Which of the following characteristics reveal about the magnetization nature of the machine? 
a) No-load characteristics 
b) Load characteristics 
c) Armature characteristics 
d) Both no-load and load characteristics 
View Answer 
Answer: d 
Explanation: Both no-load as well as load characteristics are required to predict the 
magnetization of the machine. 
2. Choose the most inappropriate out of the following for the no-load characteristics of the dc 
generator. 
a) It is the open circuit characteristic of the machine 
b) It is magnetization characteristic of the machine 
c) It is conducted on the unloaded machine 
d) None of the mentioned 
View Answer