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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. At what rate should mouth-to-mouth resuscitation be applied?
100 volts.
Circuit Breaker.
Full-load - three-phase voltage.
12 to 15 times a minute.

2. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Nearly constant.
75 turns.
200 volts AC.

3. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Isolation transformer.
Shunted and taped
They must be installed at least 7 feet above the ground.

4. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Because less current flowing at high voltage causes less line loss per kilowatt.
Continuous.
At least two phases
The sum of the two capacitors.

5. Current that changes periodically in direction is...
Alternating current.
5:1.
277 volts.
Clamp-on ammeter.

6. Not a symptom of electrical shock?.
Lower current and higher voltage.
Hyperventilation.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Because less current flowing at high voltage causes less line loss per kilowatt.

7. When not connected to a load - the secondary leads of a current transformer should be...
Hyperventilation.
Circuit Breaker.
Electro-magnetism for their operation.
Shunted and taped

8. The property of an electric circuit that opposes any change in current is called...
Inductance.
They should be made by the same manufacturer.
200 volts AC.
5:1

9. What is the first step to be followed in aiding a victim of electrical shock?
Zero amps.
Check to make sure that the victim is not still in contact with the electricity.
Nearly constant.
800 volts.

10. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Potential transformer.
They should be made by the same manufacturer.
Capacitance.
Current that changes constantly in magnitude and periodically in direction.

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

12. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
7 -630 volts.
The current will read zero.
1 amp.
25 feet.

13. AC voltage is raised or lowered by means of...
Cut around clothing that has adhered to the burned area.
Transformers.
Larger than that found in the primary winding.
They should be made by the same manufacturer.

14. A control power transformer...
Current changing constantly in magnitude and periodically in direction.
Reverse any two-phase leads.
Draw less current.
Provides single-phase power to smaller loads such as lights - heaters - etc.

15. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
1 amp.
Check to make sure that the victim is not still in contact with the electricity.
Electro-magnetism for their operation.

16. How should clothing be removed from a burn?
75 turns.
150 turns.
At least two phases
Cut around clothing that has adhered to the burned area.

17. All transformers step voltage up or down by...
150 turns.
Capacitance.
Inductance.
Reverse any two-phase leads.

18. Current in an AC circuit may be measured by...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Alternating current.
The chest should rise or inflate.
Clamp-on ammeter.

19. The main function of CT's and PT's on a main substation is to...
60 Hertz
7 -630 volts.
Allow for metering voltage and Current.
100 volts.

20. The property of an electrical circuit that opposes any change in voltage is called...
A device used to store electrical energy.
Capacitance.
Cut around clothing that has adhered to the burned area.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

21. A transformer with 1 -500 turns in the primary winding has a primary voltage of 2 -400 volts and a secondary voltage of 120 volts. How many turns are in the secondary winding?
Grounded phase and ground fault devices were not operating.
Check to make sure that the victim is not still in contact with the electricity.
75 turns.
200 volts AC.

22. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
75 turns.
An electromagnet.
150 turns.

23. Define alternating current...
Clamp-on ammeter.
100 turns.
Current changing constantly in magnitude and periodically in direction.
X.

24. If any two-phase wires are reversed on a three-phase motor - the motor will...
200 volts AC.
Reverse its rotation.
The capacitors should be discharged.
Check to make sure that the victim is not still in contact with the electricity.

25. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
The chest should rise or inflate.
Four times less than that of the secondary.
60 Hertz

26. The speed of an alternating current - squirrel-cage induction motor is...
Capacitance.
Nearly constant.
Current that changes constantly in magnitude and periodically in direction.
200 volts AC.

27. Compared to the secondary of a loaded - step-down transformer - the primary has...
15 feet off the ground.
600 volts.
7 -630 volts.
Lower current and higher voltage.

28. Which of the following does a squirrel cage induction motor have?
An electrical shock hazard may exist.
7 -630 volts.
Stator windings.
5:1.

29. What type motor is a wound-rotor induction motor?
150 turns.
600 volts.
A.C.
800 volts.

30. What type of 3-phase AC motor is used most often around a mine?
100 volts.
Transformer
Squirrel-cage induction motor.
Capacitance.

31. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Two speeds
The chest should rise or inflate.
Four times less than that of the secondary.
Stator windings.

32. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
An electrical shock hazard may exist.
Isolation transformer.
The capacitors should be discharged.

33. The primary leads of a single-phase transformer should be connected to the...
Draw less current.
Full-load - three-phase voltage.
H terminals.
Alternating current.

34. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
Larger than that found in the primary winding.
5:1
No.6 AWG.

35. The standard frequency of alternating current used at a mine is...
Circuit Breaker.
Lower current and higher voltage
60 Hertz
A.C.

36. High voltage is used to transmit power over long distances...
Derive a neutral for grounding purposes.
Because less current flowing at high voltage causes less line loss per kilowatt.
Squirrel-cage induction motor.
Lower current and higher voltage.

37. Not an acceptable method for the installations of surface transformers?
Inductance.
Reverse its rotation.
They must be installed at least 7 feet above the ground.
Four times less than that of the secondary.

38. What is the danger when working around capacitors?
An electrical shock hazard may exist.
600 volts.
At least two phases
Transformer

39. 460 volts AC is required to operate two motors - one connected in single-phase and the other connected in three-phase. The three-phase motor will...
At least two phases
Four times less than that of the secondary.
Circuit Breaker.
Draw less current.

40. 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?
A grounding resistor.
3 -979 Volts.
100 turns.
Squirrel-cage induction motor.

41. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Short-circuited after power has been removed.
Clamp-on ammeter.
Cut around clothing that has adhered to the burned area.
Isolation transformer.

42. The transformer used only to measure voltage is a...
Transformers.
Potential transformer.
7 -630 volts.
Cut around clothing that has adhered to the burned area.

43. What is a capacitor?
Draw less current.
Disconnect the frame-grounding conductor.
A device used to store electrical energy.
60 Hertz

44. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Zero amps.
277 volts.
No.6 AWG.
The chest should rise or inflate.

45. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
480 volts.
150 turns.
An electromagnet.
25 feet.

46. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Grounded phase and ground fault devices were not operating.
1 amp.
An electrical shock hazard may exist.
A grounding resistor.

47. Alternating current may be defined as...
Zero amps.
Current that changes constantly in magnitude and periodically in direction.
12 to 15 times a minute.
2000 watts

48. The primary function of a power transformer is to provide...
1 amp.
Full-load - three-phase voltage.
The chest should rise or inflate.
100 turns.

49. 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.
7 -630 volts.
2000 watts
800 volts.

50. 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?
Disconnect the frame-grounding conductor.
Reverse its rotation.
200 volts AC.
A.C.