What is the reason why a transformer is an efficient device?
AIt is a static device
BIt uses both inductive and capacitive coupling
CIts winding has less resistance
DIts friction and windage loss is small
Electrical Engineering · Question Bank
Transformers
171 of 258 questions match · page 6 of 9. Answer in your head first, then check the solution.
The increased in the kVA capacity produced by connecting a two winding transformer as an autotransformer is due to which of the following?
AIncreased in the secondary voltage
BIncreased in the transformer efficiency
CIncreased in turns ratio
DEstablishment of a conductive link between primary and secondary
What is the purpose of stampings in transformers?
ATo reduce the hysteresis loss
BTo reduce the eddy current loss
CTo reduce the copper loss
DAll of these
The cores of transformers is normally made from which of the following materials?
ASilicon steel
BSeasoned wood
CAnnealed copper
DAluminum
Which of the following is true about the primary and secondary induced emfs in a transformer?
AThey are always equal in magnitude
BThey are always anti-phase with each other
CThey are always in-phase with each other
DThey are always dependent on the load connected on the secondary side
What is the purpose of a tap changing transformer?
ATo supply low voltage for instruments
BTo step up the voltage
CTo step down the voltage
DTo step up as well as step down the voltage
Which one is an essential feature of an autotransformer?
AIt uses only one winding
BIt is more suited for single-phase supply
CIt is completely automatic in its operation
DIt is particularly suited for situations where the voltage transformation ratio exceeds unity
The core of a transformer must posses which of the following characteristics?
ALow permeability and high hysteresis
BLow permeability and low hysteresis
CHigh permeability and low hysteresis
DHigh permeability and high hysteresis
At what condition will the efficiency of a transformer be maximum?
AResistance of both windings are equal
BCopper loss is equal to core loss
CPer unit impedance of both windings are equal
DLoad served is a unity pf load
Which of the following cannot be done by a transformer?
AIncrease the output power
BIncrease the output impedance
CIncrease the output voltage
DIncrease the output current
What is the cause of the humming sound in a transformer?
ATransformer winding
BTransformer oil
CMagnetostriction
DSize of transformer tanks
The all-day efficiency of a transformer is ____ commercial efficiency of the same transformer.
AEqual to
BLess than the
CGreater than the
DEither less than or greater than the
Which loss will decrease when the load of transformer will decrease?
ACopper loss
BEddy current loss
CHysteresis loss
DAll of these
What is the purpose of using a higher flux density in a transformer?
ATo decrease the weight per kVA
BTo increase the weight per kVA
CTo decrease the weight per kW
DTo increase the weight per kW
The temperature rise in a transformer is directly proportional to which of the following?
ALeakage reactance
BSupply frequency
CApparent power
DReactive power
In general, what is the most important point to monitor during the operation of a transformer?
APrimary voltage
BCore loss
CExciting current
DTemperature
What is the percentage equivalent of the no load current in comparison to the full load current of a transformer?
AAbout 1 to 2%
BAbout 2 to 5%
CAbout 5 to 10%
DAbout 10 to 20%
Which of the following will happen when a transformer is plugged into a DC circuit?
AIt would blow a fuse
BThe secondary will burn out
CThe primary will overload and the secondary will be dead
DAll of these
Which of the following tests is used to determine the relative polarity of the windings of a transformer?
AShort circuit test
BPhasing out test
CBack to back test
DOpen circuit test
When a closed A bank is converted into an open A bank, each of the two remaining transformers supplies what percent of the original load?
A50%
B57.7%
C73.2%
D66.7%
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