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) A 50 Hz alternator is rated 500 MVA, 20 KV with Xd = 1.0 per unit and Xd"=0.2 per unit. It supplies a purely resistive load of 400 MW at 20 KV. The load is connected directly across the generator terminals when a symmetrical fault occurs at the load terminals. The initial rms current in the generator in per unit is
A) 7.22
B) 6.4
C) 3.22
D) 2.2
Ans:C
2) The direct axis reactance Xd of a synchronous generator is given as 0.4 pu based on the generator's name plate rating of 10 Kv, 75 MVA. The base for calculations is 11 KV, 100 MVA. what is the pu value of Xd on the new base?
A) 0.279
B) 0.578
C) 0.412
D) 0.44
Ans:D
3) If the excitation of a 3-phase alternator operating on infinite bus bars is changed, which one of the following shall alter?
A) Active power of machine
B) Reactive power of machine
C) Terminal voltage of machine
D) Frequency of machine
Ans:B
4) A 3-phase synchronous generator with constant steam input supplies power to an infinite bus at a lagging power factor. If the excitation is increased
A) both power angle and power factor decrease
B) both power angle and power factor increase
C) the power angle decreases while power factor increase
D) the power angle increases while power factor decreases
Ans:A
5) A turbo-alternator set feeds power to a 3-phase constant voltage, constant frequency bus. If the steam supply to the set is cut-off, then the set will
A) continue to run at rated speed in the same direction
B) continue to run at reduced speed in the same direction
C) run at rated speed in the reverse direction
D) come to stop
Ans:A
6) A stand alone engine driven synchronous generator is feeding a partly inductive load. A capacitor is now connected across the load to completely nullify inductive current. For this operating condition
A) the field current and fuel input have to be reduced
B) the field current and fuel input have to be increased
C) the field current has to be increased and fuel input left unaltered
D) the field current has to be reduced and fuel input left unaltered
Ans:D
7) The mmf produced by single phase winding is
A) pulsating and rotating with constant speed
B) pulsating and stationary
C) constant in amplitude and stationary
D) constant in amplitude and rotating
Ans:B
8) A polyphase field is
A) pulsating and stationary
B) pulsating and rotating
C) constant in amplitude and rotating at synchronous speed
D) constant in amplitude and stationary in space
Ans:C
9) When a balanced 3-phase distributed type armature winding is carrying 3-phase, balanced currents
the strength of the resultant rotating magnetic field is
A) three times the amplitude of each constituent pulsating magnetic field
B) equal to the amplitude of each constituent pulsating magnetic field
C) half the amplitude of each constituent pulsating magnetic field
D) one and half times the amplitude of each constituent pulsating magnetic field
Ans:D
10) A synchronous generator has its field winding on the rotor and armature winding on the stator. When running under steady state condition is air gap field is
A) stationary with respect to stator
B) rotating at synchronous speed with respect to rotor
C) rotating at synchronous speed against the direction of rotor rotation
D) rotating at synchronous speed in the direction of rotor rotation
Ans:D
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1) A 50 Hz alternator is rated 500 MVA, 20 KV with Xd = 1.0 per unit and Xd"=0.2 per unit. It supplies a purely resistive load of 400 MW at 20 KV. The load is connected directly across the generator terminals when a symmetrical fault occurs at the load terminals. The initial rms current in the generator in per unit is
A) 7.22
B) 6.4
C) 3.22
D) 2.2
Ans:C
2) The direct axis reactance Xd of a synchronous generator is given as 0.4 pu based on the generator's name plate rating of 10 Kv, 75 MVA. The base for calculations is 11 KV, 100 MVA. what is the pu value of Xd on the new base?
A) 0.279
B) 0.578
C) 0.412
D) 0.44
Ans:D
3) If the excitation of a 3-phase alternator operating on infinite bus bars is changed, which one of the following shall alter?
A) Active power of machine
B) Reactive power of machine
C) Terminal voltage of machine
D) Frequency of machine
Ans:B
4) A 3-phase synchronous generator with constant steam input supplies power to an infinite bus at a lagging power factor. If the excitation is increased
A) both power angle and power factor decrease
B) both power angle and power factor increase
C) the power angle decreases while power factor increase
D) the power angle increases while power factor decreases
Ans:A
5) A turbo-alternator set feeds power to a 3-phase constant voltage, constant frequency bus. If the steam supply to the set is cut-off, then the set will
A) continue to run at rated speed in the same direction
B) continue to run at reduced speed in the same direction
C) run at rated speed in the reverse direction
D) come to stop
Ans:A
6) A stand alone engine driven synchronous generator is feeding a partly inductive load. A capacitor is now connected across the load to completely nullify inductive current. For this operating condition
A) the field current and fuel input have to be reduced
B) the field current and fuel input have to be increased
C) the field current has to be increased and fuel input left unaltered
D) the field current has to be reduced and fuel input left unaltered
Ans:D
7) The mmf produced by single phase winding is
A) pulsating and rotating with constant speed
B) pulsating and stationary
C) constant in amplitude and stationary
D) constant in amplitude and rotating
Ans:B
8) A polyphase field is
A) pulsating and stationary
B) pulsating and rotating
C) constant in amplitude and rotating at synchronous speed
D) constant in amplitude and stationary in space
Ans:C
9) When a balanced 3-phase distributed type armature winding is carrying 3-phase, balanced currents
the strength of the resultant rotating magnetic field is
A) three times the amplitude of each constituent pulsating magnetic field
B) equal to the amplitude of each constituent pulsating magnetic field
C) half the amplitude of each constituent pulsating magnetic field
D) one and half times the amplitude of each constituent pulsating magnetic field
Ans:D
10) A synchronous generator has its field winding on the rotor and armature winding on the stator. When running under steady state condition is air gap field is
A) stationary with respect to stator
B) rotating at synchronous speed with respect to rotor
C) rotating at synchronous speed against the direction of rotor rotation
D) rotating at synchronous speed in the direction of rotor rotation
Ans:D
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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