Electrical Engineering · Question Bank

Transformers

258 questions · page 12 of 13. Answer in your head first, then check the solution.

📘 EE Mock Board Exam
TypeAll 258Problem solving 148Objective 110
DifficultyAll 258Easy 171Medium 71Hard 16
#221📘 EE Pocket Reviewer RojasEasy
Which one is the most common cause of contamination of water in the oil used in transformer located indoors?
ALeaky bushings
BCondensation of moisture from air in the tank
CDecomposition of foreign matters in the oil
DNone of these
#222📘 EE Pocket Reviewer RojasEasy
What is the main function of the iron core in a transformer?
ATo provide mechanical strength to the windings
BTo reduce the eddy current loss
CTo provide electrical linkage to the two windings
DTo reduce the reluctance of the magnetic path
#223📘 EE Pocket Reviewer RojasEasy
What is the relationship between the induced emf and the core flux in a transformer?
AThe induced emf lags the core flux by 90°
BThe induced emf leads the core flux by 90°
CThe induced emf is in-phase with the core flux
DThe induced emf is independent of the core flux
#224📘 EE Pocket Reviewer RojasEasy
What is the typical usage of an autotransformer?
ACurrent transformer
BVariable transformer
CIsolating transformer
DControl transformer
#225📘 EE Pocket Reviewer RojasEasy
As compared to A-A transformer bank, what is the percentage capacity of the V-V bank?
A66.7%
B86.6%
C57.7%
D73.3%
#226📘 EE Pocket Reviewer RojasEasy
What is the reason why transformers operate poorly at very low frequencies?
AMagnetizing current is high
BPermeability of the core will increase
CPrimary reactance is too much increased
DCopper loss is high
#227📘 EE Pocket Reviewer RojasEasy
What is the main purpose of having a core in a transformer?
ATo decrease the iron losses
BTo prevent the eddy current loss to happen
CTo eliminate the magnetic hysteresis
DTo decrease the reluctance of the common magnetic circuit
#228📘 EE Pocket Reviewer RojasEasy
What type of coupling is used in the primary and secondary windings of a transformer?
AElectrical
BMechanical
CMagnetic
DAll of these
#229📘 EE Pocket Reviewer RojasEasy
Which one is a method of cooling used in a transformer rated 5 kVA or less?
AOil cooled
BNatural air cooled
CHydrogen cooled
DWater cooled
#230📘 EE Pocket Reviewer RojasEasy
Tappings in a transformer are provided where?
AAt the phase end of the high voltage side
BAt the middle of the high voltage side
CAt the neutral end of the high voltage side
DAt the phase end of the low voltage side
#231📘 EE Pocket Reviewer RojasEasy
Which of the following is defined as the “voltage transformation ratio”of a transformer?
ARatio of secondary induced emf to primary induced emf
BRatio of secondary terminal voltage to primary applied voltage
CRatio of primary turns to secondary turns
DRatio of secondary current to primary current
#232📘 EE Pocket Reviewer RojasEasy
At no load, the primary input is approximately equal to the iron loss. Why?
AThe primary current is small
BThe secondary current is small
CBoth the primary and secondary currents are small
DThe transformer has no output
#233📘 EE Pocket Reviewer RojasEasy
If the impedance triangle of two transformers operating in parallel are not identical in shape and size, which of the following is true?
AThe two transformers will share the load equally
BThe two transformers will get overheated
CThe two transformers will run with different pf
DThe two transformers will have a circulating current even when unloaded
#234📘 EE Pocket Reviewer RojasEasy
What is an ideal transformer?
AA transformer that does not work
BA transformer that has only one winding
CA transformer whose primary and secondary windings are equal in turns
DA transformer that has no losses and leakage reactance
#235📘 EE Pocket Reviewer RojasEasy
What is the normal range of the efficiency of a transformer?
A90 to 98%
B80 to 90%
C70 to 80%
D60 to 70%
#236📘 EE Pocket Reviewer RojasEasy
Which one is a purpose of cooling transformers?
ATo reduce the humming sound
BTo reduce the losses
CTo increase the efficiency
DTo dissipate the heat generated in the windings
#237📘 EE Pocket Reviewer RojasEasy
During the short circuit test, which winding is short circuited?
APrimary windings
BLow voltage windings
CSecondary windings
DHigh voltage windings
#238📘 EE Pocket Reviewer RojasEasy
Under what type of load pf will a transformer have a negative voltage regulation?
AUnity pf
BLagging pf
CLeading pf
DZero pf
#239📘 EE Pocket Reviewer RojasEasy
Which one will reduce the eddy current loss in a transformer?
ABy increasing the thickness of core laminations
BBy decreasing the thickness of core laminations
CBy using higher gage wires in the windings
DBy decreasing the air gap in the magnetic circuit
#240📘 EE Pocket Reviewer RojasEasy
What is the usual secondary current rating of a current transformer used for meters and relays?
A5 A
B10 A
C1 A
D100 A or more

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