Exam: 086011rr -transformers | Electrical Engineering homework help

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Questions 1 to 20: Select the best answer to each question. Note that a question and its answers may be split across a page
break, so be sure that you have seen the entirequestion and allthe answers before choosing an answer.
1.What is the efficiency of a transformer that has an input of 600 VA and an output to a load of 580 VA?
A.180 VA
B.20 VA
C.96.6%
D.83.8%
2.Three single-phase transformers, each having a secondary phase current of 10 A, are Delta-Delta–
connected. The value of the secondary line current is
A.578 A.
B.17.3 A.
C.57.8 A.
D.1.73 A.
3.What would be the power in the secondary of a transformer that has a voltage of 48 VAC and a current
of 2.2 A?
A.52.8 watts
B.212.6 watts
C.105.6 watts
D.121.8 watts
4.What type of transformer is used to prevent electrical noise from passing from the primary winding to
the secondary winding?
A.Delta transformer
B.Oil- filled transformer
C.Dry- type transformer
D.Shielded transformer
5.Most of the transformers that you’ll find in your plant are either single-phase or
A.three- phase.
B.four- phase.
C.two- phase.
D.zero- phase.
6.A basic transformer consists of two separate conductive coils wrapped around a(n) _______ core.
A.oiled paper
B.plastic
C.copper
D.iron
7.The primary current drawn by the transformer shown will be
A.5 A.
B.50 A.
C.2 A.
D.10 A.
8.If the turns ratio of a transformer is 4 : 1 and the incoming voltage is 120 VAC, what is the secondary
voltage?
A.480 VAC
B.120 VAC
C.240 VAC
D.30 VAC
9.If the primary in a transformer has more turns than the secondary, the secondary has
A.higher power.
B.lower ampere- turns.
C.lower voltage.
D.lower current.
10.What special installation or maintenance requirements are needed for askarel-insulated transformers?
A.The oil must be changed at least once a year.
B.The radiator must be installed where air can circulate and the fins must remain clean.
C.Cooling water must be supplied to the transformer core.
D.The transformer must be installed in a vault if the voltage exceeds 35,000 VAC.
11.What type of device is used on a distribution transformer to protect the transformer from voltage
spikes?
A.A fuse
B.A pressure vent
C.A ground shield
D.A surge diverter
12.When a load is suddenly connected to a transformer, the secondary voltage will be reduced. This drop
in voltage is called transformer
A.conductance.
B.regulation.
C.seduction.
D.excitation.
13.You’ll work at times with a transformer that has one winding connected in series with the other to form
the equivalent of a single winding. This is called
A.a distribution transformer.
B.an electronic transformer.
C.an autotransformer.
D.a specialty transformer.
14.If 120 VAC is applied to a transformer with a turns ratio of 6 : 1, what type of transformer is present
and what is the output voltage of the secondary?
A.Step- up, 720 VAC
B.Step- down, 60 VAC
C.Step- down, 20 VAC
D.Step- up, 600 VAC
15.Typical potential transformers are used for
A.powering lighting systems from high- voltage feed lines.
B. biasing control circuits in high- voltage circuits.
C.powering current- sensitive relays in control circuits.
D.allowing the connection of low- voltage measuring instruments to high- voltage lines.
16.If the power in the primary circuit of a 4 : 1 transformer is 12 watts, what will be the power in the
secondary of this transformer?
A.48 watts
B.12 watts
C.4 watts
D.3 watts
17.An inductor whose reactance can be varied by supplying current through a separate DC winding is
called
A.a current transformer.
B.an autotransformer.
C.a reactance tube.
D.a saturable reactor.
End of exam
18.Why are high-quality transformers wound with large diameter wire?
A.To lower the I
2
R losses
B.To lower the hysteresis losses
C.To lower the eddy current losses
D.To lower the magnetic leakage losses
19.The secondary line-to-line voltage of a three-phase Y-Y–connected transformer bank is 115 VAC.
What would be the secondary line to neutral voltage?
A.66.4 V
B.50 V
C.84.2 V
D.199.2 V
20.What is the kVA rating of a transformer that has a secondary winding that’s delivering 10 amps at 480
VAC?
A.4800 kVA
B.480 kVA
C.48 kVA
D.4.8 kVA

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