Electrical Machines Questions and Answers – Power Factor Control of Synchronous Machines

This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “Power Factor Control of Synchronous Machines”.

1. The magnetization current drawn from an AC supply a synchronous motor is used to _________
a) set up flux in magnetic circuit of device
b) compensate core losses
c) set up magnetizing armature reaction
d) all of the mentioned
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2. A 3 phase synchronous motor is working at normal excitation, then the flux deficient in circuit is ________
a) given by armature winding mmf
b) given by field winding mmf
c) supplied to armature winding mmf
d) supplied to field winding mmf
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3. The excess flux in synchronous motor is neutralized by __________
a) armature winding by drawing demagnetizing component of the current from ac supply
b) armature winding by drawing magnetizing component of the current from ac supply
c) field winding by drawing demagnetizing component of the current from dc supply
d) field winding by drawing magnetizing component of the current from dc supply
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4. The V-curves of synchronous motor is plotted between ________
a) Ia Vs If with constant shaft load
b) If Vs Ia with constant shaft load
c) power factor vs If
d) power factor vs Ia
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5. When a constant power output is desired to maintain __________
a) Ef*sinδ and Ia*cosθ are to be maintained constant
b) Ef*sinδ is be maintained constant
c) Ia*cosθ is to be maintained constant
d) Ef*sinδ and Ia*sinθ are to be maintained constant
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6. When the excitation voltage is increased from 1 to 1.3 pu of a 3-phase synchronous motor. Then load angle for the constant power operation __________
a) must be decreased
b) can also be increased
c) increased
d) decreased
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7. The armature current is ________ at UPF when compared to leading power factor for a motor.
a) minimum
b) maximum
c) equal
d) none of the mentioned
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8. The armature current is _______ at UPF than motor at lagging power factor.
a) minimum
b) maximum
c) zero
d) none of the mentioned
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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
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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
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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
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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
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13. For a synchronous motor, mark the appropriate.

a) A-Inductor, B-Capacitor
b) A-Capacitor, B-Resistor
c) A-Inductor, B-Inductor
d) A-Capacitor, B-Inductor
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14. (I) Speed of an isolated alternator can be altered.
(II) Speed of an alternator connected to IBB can be also altered.
a) I is true, II is false
b) Both the statements are true
c) I is false while II is true
d) Both are false
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15. (I) For constant power of an isolated alternator, V-curves can be obtained.
(II) For constant power of an alternator connected to IBB, V-curves can be obtained
a) I is true, II is false
b) Both the statements are true
c) I is false while II is true
d) Both are false
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16. The operating frequency and voltage of an isolated alternator ________ if the prime mover input to motor is increased.
a) increases
b) decreases
c) remains constant
d) no relation exists between the power and frequency
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17. The active power delivered by an alternator will _______ when the prime mover input is increased for the alternator connected to infinite bus bar.
a) increases
b) decreases
c) remains constant
d) no relation exists between the power and prime mover droop characteristic
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Sanfoundry Global Education & Learning Series – Electrical Machines.

To practice all areas of Electrical Machines, here is complete set of 1000+ Multiple Choice Questions and Answers.