Electrical Machines Questions and Answers_pag150

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Answer: a 
Explanation: At leading pf armature current will be high as the emf will be high for a 
synchronous motor. 
9. The inverted V plots is plotted between 
a) power factor vs field current for constant shaft load 
b) field current vs power factor for variable shaft load 
c) armature current vs field current 
d) terminal voltage vs power factor 
View Answer 
Answer: a 
Explanation: inverted v-curves are plotted between power factor and field current for constant 
shaft load. 
10. For a power system having induction motor loads, an overexcited synchronous motor is also 
attached. Then the over all power factor 
a) improves 
b) degrades 
c) becomes upf 
d) remains same 
View Answer 
Answer: a 
Explanation: An over excited synchronous motor acts as a source of lagging reactive power and 
so the overall power factor improves. 
11. For a power system having induction motor loads, an overexcited synchronous motor is also 
attached. The induction motor will now operate at 
a) lagging 
b) leading 
c) reduced power factor 
d) increased power factor 
View Answer 
Answer: a 
Explanation: Adding synchronous motor will improve the pf of the system but then the induction 
motor will still work at lagging pf only. 
12. Synchronous compensators are 
a) overexcited synchronous motor with no mechanical load 
b) overexcited synchronous motor with mechanical load 
c) underexcited synchronous motor with no mechanical load 
d) normal excited synchronous motor with no mechanical load 
View Answer 
Answer: a 
Explanation: Synchronous compensators are overexcited synchronous motor with no 
mechanical load. 
13. For a synchronous motor, mark the appropriate.