Questions 1:
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 entire question and all the answers before choosing an answer.
1. A basic transformer consists of two separate conductive coils wrapped around a(n) core.
A. iron
B. oiled paper
C. copper
D. plastic
2. An inductor whose reactance can be varied by supplying current through a separate DC winding is called
A. an autotransformer.
B. a current transformer.
C. a saturable reactor.
D. a reactance tube.
3. 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. 4 watts
B. 12 watts
C. 3 watts
D. 48 watts
4. What type of device is used on a distribution transformer to protect the transformer from voltage spikes?
A. A surge diverter
B. A pressure vent
C. A fuse
D. A ground shield
5. 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. 199.2 V
B. 84.2 V
C. 66.4 V
D. 50 V
6. When a load is suddenly connected to a transformer, the secondary voltage will be reduced. This drop in
voltage is called transformer
A. excitation.
B. seduction.
C. conductance.
D. regulation.
7. Most of the transformers that you'll find in your plant are either single-phase or
A. three-phase.
B. zero-phase.
C. two-phase.
D. four-phase.
8. The primary current drawn by the transformer shown will be
A. 2 A.
B. 50 A.
C. 10 A.
D. 5 A.
9. If the primary in a transformer has more turns than the secondary, the secondary has
A. lower voltage.
B. higher power.
C. lower current.
D. lower ampere-turns.
10. 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. 57.8 A.
B. 17.3 A.
C. 578 A.
D. 1.73 A.
11. What special installation or maintenance requirements are needed for askarel-insulated transformers?
A. Cooling water must be supplied to the transformer core.
B. The transformer must be installed in a vault if the voltage exceeds 35,000 VAC.
C. The oil must be changed at least once a year.
D. The radiator must be installed where air can circulate and the fins must remain clean.
12. What is the efficiency of a transformer that has an input of 600 VA and an output to a load of 580 VA?
A. 20 VA
B. 96.6%
C. 180 VA
D. 83.8%
13. 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. 4.8 kVA
D. 48 kVA
14. Typical potential transformers are used for
A. powering lighting systems from high-voltage feed lines.
B. allowing the connection of low-voltage measuring instruments to high-voltage lines.
C. powering current-sensitive relays in control circuits.
D. biasing control circuits in high-voltage circuits.
15. What type of transformer is used to prevent electrical noise from passing from the primary winding to the secondary winding?
A. Shielded transformer
B. Oil-filled transformer
C. Dry-type transformer
D. Delta transformer
16. If the turns ratio of a transformer is 4 : 1 and the incoming voltage is 120 VAC, what is the secondary voltage?
A. 120 VAC
B. 30 VAC
C. 480 VAC
D. 240 VAC
17. Why are high-quality transformers wound with large diameter wire?
A. To lower the hysteresis losses
B. To lower the magnetic leakage losses
C. To lower the eddy current losses
D. To lower the I2R losses
18. 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. an autotransformer.
B. a distribution transformer.
C. a specialty transformer.
D. an electronic transformer.
19. 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-down, 60 VAC
B. Step-up, 720 VAC
C. Step-down, 20 VAC
D. Step-up, 600 VAC
20. 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. 105.6 watts
B. 52.8 watts
C. 121.8 watts
D. 212.6 watts