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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?
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
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?
4.What type of transformer is used to prevent electrical noise from passing from the primary winding to
the secondary winding?
B.Oil- filled transformer
C.Dry- type transformer
5.Most of the transformers that you’ll find in your plant are either single-phase or
6.A basic transformer consists of two separate conductive coils wrapped around a(n) _______ core.
7.The primary current drawn by the transformer shown will be
8.If the turns ratio of a transformer is 4 : 1 and the incoming voltage is 120 VAC, what is the secondary
9.If the primary in a transformer has more turns than the secondary, the secondary has
B.lower ampere- turns.
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
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
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.
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?
17.An inductor whose reactance can be varied by supplying current through a separate DC winding is
A.a current transformer.
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
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?
20.What is the kVA rating of a transformer that has a secondary winding that’s delivering 10 amps at 480
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