Electrical Machines Questions and Answers_pag160

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9. The phasor diagram of a synchronous machine connected to an infinite bus is shown in the 
figure. 
 
The machine is acting as 
a) generator and operating at leading pf 
b) generator and operating at lagging pf 
c) motor and operating at leading pf 
d) motor and operating at lagging pf 
View Answer 
Answer: a 
Explanation: The induced voltage leads the bus voltage, which means that it is at leading pf and 
then excitation magnitude is also more than terminal bus voltage. 
10. If the excitation of a 3-phase alternator operating on infinite bus bars is changed, which one 
of the following will get affected? 
a) Active real power of machine 
b) Reactive power of machine 
c) Terminal voltage of machine 
d) Frequency of machine 
View Answer 
Answer: b 
Explanation: Excitation is coupled with the reactive power of the machine majorly. 
11. In which one of the following is reluctance power developed? 
a) Salient pole alternator 
b) Non-salient pole alternator 
c) Squirrel cage rotor type induction motor 
d) All of the mentioned 
View Answer 
Answer: a 
Explanation: Because there is variable air gap due to saliency of the poles. 
12. While conducting measurement for Xd and Xq, the information obtained is below 
Id max = 10 A; Id min = 5 A 
Vd max = 30 V; Vd min = 25 V 
Which one of the following is correct? 
a) Xd = 3, Xq = 2.5