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AC Theory

Instructions:

Answer 50 questions in 15 minutes.
If you are not ready to take this test, you can study here.
Match each statement with the correct term.
Don't refresh. All questions and answers are randomly picked and ordered every time you load a test.

This is a study tool. The 3 wrong answers for each question are randomly chosen from answers to other questions. So, you might find at times the answers obvious, but you will see it re-enforces your understanding as you take the test each time.

1. Operating coils - motors - transformers - relays and solenoids depend upon...
It provides good speed control.
Electro-magnetism for their operation.
Derive a neutral for grounding purposes.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

2. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
12 to 15 times a minute.
75 turns.
2000 watts
No.6 AWG.

3. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
The motor rotation is reversed.
3 -979 Volts.
Continuous.

4. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Transformers.
Short-circuited after power has been removed.
Grounded phase and ground fault devices were not operating.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

5. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Because less current flowing at high voltage causes less line loss per kilowatt.
An electromagnet.
277 volts.
15 feet off the ground.

6. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
At the source transformer.
At least two phases
A step-up transformer.
The motor rotation is reversed.

7. AC voltage is raised or lowered by means of...
Transformers.
3 -979 Volts.
Reverse its rotation.
25 feet.

8. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Grounded phase and ground fault devices were not operating.
Lower current and higher voltage.
75 turns.

9. The property of an electric circuit that opposes any change in current is called...
No.6 AWG.
Inductance.
Lower current and higher voltage.
25 feet.

10. Not a symptom of electrical shock?.
100 turns.
Hyperventilation.
480 volts.
Four times less than that of the secondary.

11. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
480 volts.
7 -630 volts.
60 Hertz
Squirrel-cage rotor.

12. Which of the following does a squirrel cage induction motor have?
Current that changes constantly in magnitude and periodically in direction.
H terminals.
Stator windings.
Kilovolt ampere (KVA).

13. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
An electrical shock hazard may exist.
The chest should rise or inflate.
5:1.
60 cycles per second (60 Hertz).

14. A burn causing a blister is classified as a...
Second-degree burn.
A step-up transformer.
100 turns.
Inductance.

15. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Full-load - three-phase voltage.
75 turns.
Shunted and taped

16. How should clothing be removed from a burn?
The motor rotation is reversed.
Squirrel-cage induction motor.
1 amp.
Cut around clothing that has adhered to the burned area.

17. What is the danger when working around capacitors?
An electrical shock hazard may exist.
25 feet.
Squirrel-cage induction motor.
Allow for metering voltage and Current.

18. Current transformers - or CT's - are used to...
Four times less than that of the secondary.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
They should be made by the same manufacturer.
75 turns.

19. What position of a selector switch using a voltmeter would you select to check a 120-volt AC circuit to obtain the most accurate reading?
200 volts AC.
15 feet off the ground.
A grounding resistor.
Draw less current.

20. A transformer has a primary voltage of 2 -400 volts and a secondary reading of 120 volts. If there are 1 -500 turns on the primary - how many turns are on the secondary?
100 turns.
2000 watts
They must be installed at least 7 feet above the ground.
75 turns.

21. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
Grounded phase and ground fault devices were not operating.
Cut around clothing that has adhered to the burned area.
Second-degree burn.

22. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
No.6 AWG.
Isolation transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.

23. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
277 volts.
The current will read zero.
100 turns.
The sum of the two capacitors.

24. At what rate should mouth-to-mouth resuscitation be applied?
Inductance.
12 to 15 times a minute.
Circuit Breaker.
Cut around clothing that has adhered to the burned area.

25. What type of 3-phase AC motor is used most often around a mine?
Full-load - three-phase voltage.
Squirrel-cage induction motor.
Reverse its rotation.
Grounded phase and ground fault devices were not operating.

26. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Kilovolt ampere (KVA).
Transformers.
Four times less than that of the secondary.
480 volts.

27. A transformer has a primary voltage of 2 -800 volts and a secondary reading of 140 volts. If there are 2000 turns on the primary - how many turns are on the secondary?
5:1.
100 turns.
800 volts.
The motor rotation is reversed.

28. The most reliable method to use to determine whether or not the heart has stopped is by checking the...

29. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Cut around clothing that has adhered to the burned area.
Disconnect the frame-grounding conductor.
They must be installed at least 7 feet above the ground.
2000 watts

30. All transformers step voltage up or down by...
75 turns.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Inductance.
Continuous.

31. What is the first step to be followed in aiding a victim of electrical shock?
60 cycles per second (60 Hertz).
7 -630 volts.
Check to make sure that the victim is not still in contact with the electricity.
Squirrel-cage induction motor.

32. Current in an AC circuit may be measured by...
Grounded phase and ground fault devices were not operating.
5:1.
They must be installed at least 7 feet above the ground.
Clamp-on ammeter.

33. The size of a transformer is measured in...
Capacitance.
Inductance.
Kilovolt ampere (KVA).
H terminals.

34. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
They must be installed at least 7 feet above the ground.
3 -979 Volts.
277 volts.

35. Current that changes periodically in direction is...
They must be installed at least 7 feet above the ground.
Alternating current.
Disconnect the frame-grounding conductor.
100 volts.

36. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
The sum of the two capacitors.
277 volts.
Grounded phase and ground fault devices were not operating.
An electrical shock hazard may exist.

37. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
100 turns.
At the source transformer.
Draw less current.
Two speeds

38. What value of voltage will be measured from phase-to-phase - in a wye-connected secondary - if 2 -300 volts is measured from phase-to-ground?
Lower current and higher voltage.
Hyperventilation.
No.6 AWG.
3 -979 Volts.

39. The speed of an alternating current - squirrel-cage induction motor is...
150 turns.
Grounded phase and ground fault devices were not operating.
Nearly constant.
3 -979 Volts.

40. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
A step-up transformer.
Isolation transformer.
150 turns.

41. A control power transformer...
It provides good speed control.
60 Hertz
Provides single-phase power to smaller loads such as lights - heaters - etc.
15 feet off the ground.

42. Not true about AC power?
The sum of the two capacitors.
Second-degree burn.
15 feet off the ground.
It provides good speed control.

43. A 3-phase - 2 speed - constant torque motor is running at fast speed. The motor windings are connected wye for fast speed. Motor leads T4 - T5 and T6 are connected to the line leads. Motor leads T1 - T2 and T3 should be...
Cut around clothing that has adhered to the burned area.
The motor rotation is reversed.
Tied together
Because less current flowing at high voltage causes less line loss per kilowatt.

44. Compared to the secondary of a loaded - step-down transformer - the primary has...
Capacitance.
Lower current and higher voltage
12 to 15 times a minute.
Alternating current.

45. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Four times less than that of the secondary.
Draw less current.
600 volts.
Full-load - three-phase voltage.

46. Where should grounding resistors be located?
Provides single-phase power to smaller loads such as lights - heaters - etc.
Derive a neutral for grounding purposes.
1 amp.
At the source transformer.

47. A transformer with 3000 turns in the primary winding has a primary voltage of 4 -800 volts and a secondary voltage of 240 volts. How many turns are in the secondary winding?
Inductance.
The current will read zero.
150 turns.
200 volts AC.

48. Two 10-hp induction motors are operating on 460 volts AC. One motor is connected by single- phase; the other is connected in three-phase. The three-phase will...
Inductance.
Reverse its rotation.
Draw less current.
60 cycles per second (60 Hertz).

49. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
Potential transformer.
Allow for metering voltage and Current.
Alternating current.

50. A wound-rotor induction motor has all the following EXCEPT...
An electromagnet.
Squirrel-cage rotor.
Kilovolt ampere (KVA).
3 -979 Volts.