When an alternator connected to a bus bar is shut down, what happens to the bus bar voltage?
AThe voltage will decrease
BThe voltage will increase
CThe voltage will remain the same
DThe voltage will fall down to zero
Electrical Engineering · Question Bank
Alternators
109 of 157 questions match · page 4 of 6. Answer in your head first, then check the solution.
When running under steady state conditions, which one represents the air gap field of the alternator?
AIt is stationary with respect to the stator
BIt is rotating at synchronous speed against the direction of rotor rotation
CIt is rotating at synchronous speed with respect to rotor
DIt is rotating at synchronous speed in the direction of rotor rotation
What do you mean by the phrase “synchronization” of alternators?
AConnecting alternators in parallel
BAdjusting excitation on alternators
CAdjusting input torque on alternators
DRunning alternators at their synchronous speed
What is the size of an alternator in comparison to a dc generator, assuming they have the same power ratings?
AThe alternator is bigger in size
BThe alternator is smaller in size
CBoth machines have the same sizes
DEither A, or B or
When two or more alternators are in parallel operation, their kVAR load share is changed by changing which of the following?
ADriving torque
BExcitation
CEither A or
DBoth A and B simultaneously
A synchronous generator is connected to a power station. What will happen if the excitation is increased?
AThe reactive power generated will decrease
BThe reactive power generated will increase
CThe active power generated will increase
DThe active power generated will decrease
Which of the following refers to the synchronous reactance of the alternator?
AThe sum of the armature reaction reactance and the leakage reactance
BA reactance connected in series with the alternator to reduce the fault current
CThe leakage reactance only
DThe reactance due to armature resistance
What is the reason why the voltage regulation of an alternator is larger than the voltage regulation of a dc generator?
ADue to large armature resistance
BDue to large leakage reactance
CDue to complex effect of the armature reaction
DAll of these
Salient rotor type for alternators are used in which of the following applications?
AHigh speed prime mover is available
BLow speed prime mover is available
CMedium speed prime mover is available
DEither B or
An AC generator is run at 10% overload. What will happen?
ANo danger will occur
BThe brushes will spark excessively
CThe circuit breaker will kick out
DThe generator power factor will increase
What is the purpose of the frame of an alternator?
AIt is used to ventilate the armature
BIt is used as a return path for the field flux
CIt is used to hold the armature stampings
DIt is used to protect the operator of the machine
What is the purpose of using damper windings in alternators?
ATo prevent hunting
BTo achieve synchronism
CTo reduce friction and windage
DTo prevent the alternator from power reversal
In an alternator, the magnitude of the various voltage drops depends on which of the following?
ALoad current
BPower factor of the load
CSquare of the load current
DPower factor x load current
If the driving power from the prime mover driving ' the alternator is lost but the alternator remains connected to the bus bars with its field still excited, what will happen?
AThe alternator will run as a synchronous motor and will rotate in the same direction
BThe alternator will run as a synchronous motor and will rotate in the opposite direction
CThe alternator will still run as a synchronous generator but with less efficiency
DThe alternator will overload and get burned
The voltage regulation of an alternator is negative when the alternator is serving what type of load pf?
AZero pf
BUnity pf
CLeading pf
DLagging pf
The synchronous impedance of an alternator is defined as the ratio of which of the following?
AShort circuit voltage to short circuit current
BOpen circuit voltage to open circuit current
CShort circuit voltage to open circuit current
DOpen circuit voltage to short circuit current
In an alternator, the flux created by the armature mmf subtracts directly from the main flux for which of the following condition of load?
ALoad pf is zero leading
BLoad pf is zero lagging
CLoad pf is unity
DLoad pf is 0.8 lagging
The voltage of the field windings of an alternator is usually what value?
ALess than 200
BBetween 200 V and 440
CBetween 440 V and 1 kV
DMore than 1 kV
A three-phase synchronous generator is operating at 0.8 pf lagging with respect to the excitation voltage. What is the nature of the mmf produced by the armature current?
AIt has magnetizing effect
BIt has demagnetizing effect
CIt has cross-magnetizing effect only
DIt has partly demagnetizing and partly cross-magnetizing effects
Under what load power factor will the armature flux cross magnetizes the main field flux?
AZero pf
BUnity pf
CLeading pf
DLagging pf
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