Hi friends, this post is about objectives of synchronous machine. Mcq's on synchronous machines which are asked recently in various competitive exams like Gate , Upsc exams and so on. check out and comment if you have any doubts regarding this bits..
1) The magnitude of leakage flux depends on
A) the magnitude of armature current
B) phase angle between armature current and terminal voltage
C) air gap thickness
D) both (a) and (b)
Ans:D
2) A 3-phase alternator rated at 50 MVA, 22 KV has a synchronous reactance per phase of 5 pu on its thermal rating. The pu value of this reactance on a base of 100 MVA and 220 KV is
A) 25 pu
B) 12.5 pu
C) 1 pu
D) 0.1 pu
Ans:D
3) A 3-phase 50 MVA, 10 KV generator has reactance of 0.2 ohm per phase. Hence the per-unit value of the reactance on a base 100 MVA 25 KV will be
A) 1.25
B) 0.625
C) 0.032
D) 0.32
Ans:C
4) Three generators rated 100 MVA, 11 KV have an impedance of 0.15 pu each. If in the same plant, these generators are being replaced by a single equivalent generator, the effective impedance of equivalent generator will be
A) 0.05 pu
B) 0.15 pu
C) 0.25 pu
D) 0.45 pu
Ans:A
5) Leakage reactance of the armature of a salient pole synchronous machine which varies with the position of rotor is due to leakage flux
A) of end connections
B) which comes out of slot teeth, crosses the air-gap and enters the pole faces
C) which remains within the slot
D) none of the above
Ans:B
6) In a synchronous generator
A) the armature mmf leads the air-gap flux and air-gap flux leads the field mmf.
B) the armature mmf leads the air-gap flux and air-gap flux lags behind the field mmf.
C) the armature mmf lags behind the air-gap flux and air-gap flux lags behind the field mmf.
D) the armature mmf lags behind the air-gap and air-gap flux leads the field mmf.
Ans:C
7) Armature reaction effect is/are ............ on the main field flux
A) distorting (or cross-magnetizing) as well as demagnetizing
B) only assisting
C) only demagnetizing
D) only distorting
Ans:A
8) The armature reaction effect in a synchronous machine depends on
A) load current
B) power factor of the load
C) speed of the machine
D) both (a) and (b)
Ans:D
9) In a synchronous generator, the effect of cross-magnetization is to make the generated voltage
A) truely sinusoidal
B) non-sinusoidal
C) free from harmonics
D) none of these
Ans:B
10) In an alternator, the armature reaction is considered to be equivalent to a fictitious
A) reactance
B) resistance
C) impedance
D) admittance
Ans:A
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1) The magnitude of leakage flux depends on
A) the magnitude of armature current
B) phase angle between armature current and terminal voltage
C) air gap thickness
D) both (a) and (b)
Ans:D
2) A 3-phase alternator rated at 50 MVA, 22 KV has a synchronous reactance per phase of 5 pu on its thermal rating. The pu value of this reactance on a base of 100 MVA and 220 KV is
A) 25 pu
B) 12.5 pu
C) 1 pu
D) 0.1 pu
Ans:D
3) A 3-phase 50 MVA, 10 KV generator has reactance of 0.2 ohm per phase. Hence the per-unit value of the reactance on a base 100 MVA 25 KV will be
A) 1.25
B) 0.625
C) 0.032
D) 0.32
Ans:C
4) Three generators rated 100 MVA, 11 KV have an impedance of 0.15 pu each. If in the same plant, these generators are being replaced by a single equivalent generator, the effective impedance of equivalent generator will be
A) 0.05 pu
B) 0.15 pu
C) 0.25 pu
D) 0.45 pu
Ans:A
5) Leakage reactance of the armature of a salient pole synchronous machine which varies with the position of rotor is due to leakage flux
A) of end connections
B) which comes out of slot teeth, crosses the air-gap and enters the pole faces
C) which remains within the slot
D) none of the above
Ans:B
6) In a synchronous generator
A) the armature mmf leads the air-gap flux and air-gap flux leads the field mmf.
B) the armature mmf leads the air-gap flux and air-gap flux lags behind the field mmf.
C) the armature mmf lags behind the air-gap flux and air-gap flux lags behind the field mmf.
D) the armature mmf lags behind the air-gap and air-gap flux leads the field mmf.
Ans:C
7) Armature reaction effect is/are ............ on the main field flux
A) distorting (or cross-magnetizing) as well as demagnetizing
B) only assisting
C) only demagnetizing
D) only distorting
Ans:A
8) The armature reaction effect in a synchronous machine depends on
A) load current
B) power factor of the load
C) speed of the machine
D) both (a) and (b)
Ans:D
9) In a synchronous generator, the effect of cross-magnetization is to make the generated voltage
A) truely sinusoidal
B) non-sinusoidal
C) free from harmonics
D) none of these
Ans:B
10) In an alternator, the armature reaction is considered to be equivalent to a fictitious
A) reactance
B) resistance
C) impedance
D) admittance
Ans:A
If you like my post please share it with your friends and subscribe to latest updates.. If you have doubts you can start new topic on forum and start discussion with our readers..
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