What is the purpose of hydrogen in a large alternator?
ATo strengthen the magnetic field
BTo cool the alternator
CTo reduce the eddy current loss
DTo reduce distortion of the waveform
Electrical Engineering · Question Bank
Alternators
94 of 157 questions match · page 2 of 5. Answer in your head first, then check the solution.
Which of the following is not required in the parallel operation of alternators?
AThey must have the same terminal voltage
BThey must have the same phase rotation
CThey must have the same frequency
DThey must have equal ratings
Which of the following coils is the generated emf be more, for a given flux and number of turns?
AFull pitch coil
BShort pitch coil
COver pitch coil
DAll of these will generate equal emf
What is the reason why hydrogen is used for cooling of large size generators?
AIt is light
BIt offers reduced fire risk
CIt has high thermal conductivity
DAll of these
Which of the following describes the rotor used in turbo alternators?
ASmall diameter and long axial length
BLarge diameter and short axial length
CLarge diameter and long axial length
DSmall diameter and short axial length
Two alternators A and B are operating in parallel and sharing equally a unity pf load. If the excitation of A is increased, which of the following will happen?
AA will become lagging while B will become leading
BA will become leading while B will become lagging
CBoth A and B will operate on leading pf
DBoth A and B will operate on lagging pf
In a big alternator, which one is the moving part?
AYoke
BPoles
CArmature
DCommutator
At leading power factor, what is the effect of the armature flux of the alternator to its rotor flux?
AIt will aid
BIt will distort
CIt will oppose
DIt does not have any effect
What type of voltage is being:applied to the field windings of an alternator?
AHigh dc voltage
BLow dc voltage
CHigh ac voltage
DLow ac voltage
In an alternator, what relationship is being shown in a magnetization curve?
AMagnetic flux vs excitation current
BReactive power vs real power
CExcitation current vs terminal voltage
DLoad current vs excitation current
Which of the following methods are commonly used in synchronizing alternators?
ADark lamp method only
BBright lamp method only
CDark lamp method and a synchroscope
DBright lamp method and a synchroscope
Pitch factor is defined as the ratio of the voltage induced in a
AFull pitch coil to a short pitch coil
BShort pitch coil to a full pitch coil
CShort pitch coil to a long pitch coil
DLong pitch coil to a short pitch coil
What will happen if a high speed alternator uses salient poles?
AReduced windage loss but excessive noise
BReduced windage loss and lesser noise
CExcessive windage loss and excessive noise
DExcessive windage loss but reduced noise
When two or more alternators are in parallel operation, their kW load share is changed by changing which of the following?
ADriving torque
BExcitation
CEither A or
DBoth A and B simultaneously
Low speed alternators are driven by which of the following prime movers?
ASteam turbines
BHydraulic turbines
CSteam engines
DAny of these
What is the reason why it is not advisable to connect a stationary alternator to a live bus bars?
AIt will get short circuited
BIt will likely to run as a synchronous motor
CIt will cause the bus bar voltage to increase
DIt will disturb the generated emf of the other alternators connected in the bus
If the prime mover of an alternator supplying a load to an infinite bus is suddenly shut down what will happen to the alternator?
AIt will stop running
BIt will continue to run as an alternator
CIt will continue to run as a synchronous motor in the reverse direction
DIt will continue to run as a synchronous motor in the same direction
Alternators uses normally what type of field?
ARotating field type
BStationary field type
CEither
DNone of these
When an alternator is supplying a zero lagging pf load, the armature reaction will produce which of the following conditions?
ADemagnetization of the main field flux
BMagnetization of the main field flux
CCross magnetization of the main field flux
DAll of these
Which of the following alternator parts plays an important role in over speed protection?
ACircuit breaker
BOverload relay
CGovernor
DDifferential protection
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