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
Electrical Engineering · Question Bank
Alternators
157 questions · page 7 of 8. Answer in your head first, then check the solution.
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
Two alternators are operating in parallel, if the load shared by one of the alternators is to be increased, what will the operator do the alternator?
AKeep its input torque constant and increase its excitation
BDecrease its excitation and input torque simultaneously
CKeep the excitation constant and increase its input torque
DNone of these
For proper parallel operation alternators, which of the following alternator ratings must be the same?
ARated speed
BVoltage rating
CExcitation
DkVA rating
The slip rings employed in a three-phase alternator in a hydro station are insulated for which of the following voltage levels?
ALow voltage
BHigh voltage
CExtra high voltage
DVery low voltage
What is the advantage of distributing the windings in an alternator?
AIt will reduce harmonics
BIt will prevent vibrations
CIt will save on copper wires
DIt will improve voltage waveform
What is an exciter?
AA synchronous generator
BA dc shunt generator
CA synchronous motor run without a load
DA dc shunt motor run without a load
Two alternators A and B are operating in parallel sharing equally a lagging pf load. If the excitation of alternator A is increased, what happens to the current delivered by each alternators?
AAlternator A will deliver more current than
BAlternator A will deliver lesser current than
CAlternators A and B will continue to deliver the same amount of current as before
DNone of these
As the load power factor of an alternator becomes more leading, what will happen to the generated voltage required to give rated terminal voltage?
AIt will decrease
BIt will increase
CIt will remain the same
DIt will become unpredictable
In alternators, the so-called “dark and bright lamp” method is used for which of the following?
ADetermining the operating phase sequence
BDetermining voltage regulation at a given load
CIn transferring load between alternators
DIn synchronizing alternators
Which of the following prime movers of an alternator do not have the tendency to hunt?
AHydraulic turbines
BDiesel engines
CSteam turbines
DAll of these
The power factor of an alternator is determined from which of the following?
AExcitation
BPrime mover
CLoad
DSpeed
An over-excited alternator is operating under what load power factor?
ALeading pf
BZero pf
CLagging pf
DUnity pf
Two identical alternators A and B are running in parallel sharing equally a common load. If the excitation of alternator B is increased without changing its steam supply, then ____
AkVAR supplied by B will decrease
BkW supplied by B will be almost the same
CkVA supplied by B will decrease
DPower factor of B will increase
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