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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. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
The current will read zero.
A step-up transformer.
Lower current and higher voltage.
Current changing constantly in magnitude and periodically in direction.

2. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
At the source transformer.
Transformer
The chest should rise or inflate.
Check to make sure that the victim is not still in contact with the electricity.

3. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Current changing constantly in magnitude and periodically in direction.
Draw less current.
Stator windings.
Two speeds

4. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Hyperventilation.
An electrical shock hazard may exist.
The capacitors should be discharged.
Inductance.

5. Under fault conditions - the grounding resistor in a high voltage circuit limits the voltage drop in the grounding circuit external to the resistor to not more than...
5:1.
At the source transformer.
100 volts.
Inductance.

6. If any two-phase wires are reversed on a three-phase motor - the motor will...
Zero amps.
Reverse its rotation.
Transformer
5:1.

7. The primary leads of a single-phase transformer should be connected to the...
5:1.
Alternating current.
H terminals.
Two speeds

8. What is a capacitor?
Larger than that found in the primary winding.
2000 watts
A device used to store electrical energy.
60 cycles per second (60 Hertz).

9. The speed of an alternating current - squirrel-cage induction motor is...
A step-up transformer.
An electrical shock hazard may exist.
60 Hertz
Nearly constant.

10. The property of an electrical circuit that opposes any change in voltage is called...
Current changing constantly in magnitude and periodically in direction.
An electrical shock hazard may exist.
Capacitance.
At least two phases

11. 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?
150 turns.
X.
3 -979 Volts.
At least two phases

12. The standard frequency of alternating current used at a mine is...
60 Hertz
1 amp.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Reverse any two-phase leads.

13. A burn causing a blister is classified as a...
Cut around clothing that has adhered to the burned area.
15 feet off the ground.
The current will read zero.
Second-degree burn.

14. What type of 3-phase AC motor is used most often around a mine?
The chest should rise or inflate.
Reverse its rotation.
150 turns.
Squirrel-cage induction motor.

15. Current that changes periodically in direction is...
Alternating current.
15 feet off the ground.
2000 watts
75 turns.

16. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
It provides good speed control.
Reverse its rotation.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

17. A solenoid coil is...
A grounding resistor.
An electromagnet.
A device used to store electrical energy.
1 amp.

18. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
277 volts.
Squirrel-cage induction motor.
Lower current and higher voltage.
15 feet off the ground.

19. 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...
Stator windings.
At least two phases
Derive a neutral for grounding purposes.
Tied together

20. 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?
Current changing constantly in magnitude and periodically in direction.
100 turns.
25 feet.
Inductance.

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

22. When not connected to a load - the secondary leads of a current transformer should be...
Larger than that found in the primary winding.
Nearly constant.
Hyperventilation.
Shunted and taped

23. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Derive a neutral for grounding purposes.
The motor rotation is reversed.
3 -979 Volts.
They must be installed at least 7 feet above the ground.

24. What is the danger when working around capacitors?
They should be made by the same manufacturer.
An electrical shock hazard may exist.
Electro-magnetism for their operation.
100 turns.

25. Current transformers - or CT's - are used to...
A grounding resistor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
H terminals.
Lower current and higher voltage

26. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
The sum of the two capacitors.
60 Hertz
Four times less than that of the secondary.
3 -979 Volts.

27. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Four times less than that of the secondary.
480 volts.
An electromagnet.
60 Hertz

28. The standard frequency of power supplied by the power company is...
At least two phases
Transformers.
60 cycles per second (60 Hertz).
Draw less current.

29. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
Larger than that found in the primary winding.
60 Hertz
They should be made by the same manufacturer.

30. Not a symptom of electrical shock?.
Hyperventilation.
Inductance.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Lower current and higher voltage

31. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Alternating current.
100 volts.
7 -630 volts.

32. 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.
The chest should rise or inflate.
1 amp.
Larger than that found in the primary winding.

33. The primary function of a power transformer is to provide...
100 volts.
12 to 15 times a minute.
Stator windings.
Full-load - three-phase voltage.

34. A wound-rotor induction motor has all the following EXCEPT...
5:1.
No.6 AWG.
25 feet.
Squirrel-cage rotor.

35. A transformer has 2000 turns in the primary and 500 turns in the secondary. The primary voltage is 3 -200 volts. What is the secondary voltage?
800 volts.
Inductance.
Second-degree burn.
Clamp-on ammeter.

36. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The current will read zero.
Cut around clothing that has adhered to the burned area.
Current that changes constantly in magnitude and periodically in direction.
Draw less current.

37. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
2000 watts
75 turns.
Second-degree burn.

38. How do you change the direction of a 3-phase AC motor?
Provides single-phase power to smaller loads such as lights - heaters - etc.
Larger than that found in the primary winding.
Cut around clothing that has adhered to the burned area.
Reverse any two-phase leads.

39. What steps up or steps down AC voltage?
They must be installed at least 7 feet above the ground.
Transformer
Reverse any two-phase leads.
25 feet.

40. 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?
Alternating current.
Grounded phase and ground fault devices were not operating.
150 turns.
The sum of the two capacitors.

41. Alternating current may be defined as...
A grounding resistor.
Current that changes constantly in magnitude and periodically in direction.
Electro-magnetism for their operation.
5:1

42. Not true about AC power?
A step-up transformer.
They should be made by the same manufacturer.
Stator windings.
It provides good speed control.

43. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Squirrel-cage induction motor.
Potential transformer.
Shunted and taped

44. Three-phase AC underground cables must be provided with overcurrent protection using a...
The sum of the two capacitors.
Circuit Breaker.
Lower current and higher voltage.
Inductance.

45. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Two speeds
X.
2000 watts
Continuous.

46. A transformer has 1 -600 turns in the primary and 400 turns in the secondary. The primary voltage is 2 -400 volts. What is the secondary voltage?
The sum of the two capacitors.
600 volts.
3 -979 Volts.
Tied together

47. Compared to the secondary of a loaded - step-down transformer - the primary has...
Squirrel-cage rotor.
Lower current and higher voltage.
800 volts.
5:1

48. Where should grounding resistors be located?
Nearly constant.
At the source transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
Squirrel-cage induction motor.

49. Current in an AC circuit may be measured by...
Clamp-on ammeter.
100 volts.
150 turns.
Because less current flowing at high voltage causes less line loss per kilowatt.

50. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Squirrel-cage rotor.
Check to make sure that the victim is not still in contact with the electricity.
The sum of the two capacitors.