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AC Theory

Instructions:

Answer 50 questions in 15 minutes.
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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 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?
A device used to store electrical energy.
Isolation transformer.
277 volts.
75 turns.

2. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
60 cycles per second (60 Hertz).
Shunted and taped
3 -979 Volts.
The chest should rise or inflate.

3. Compared to the secondary of a loaded - step-down transformer - the primary has...
Capacitance.
Continuous.
Lower current and higher voltage
Larger than that found in the primary winding.

4. 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.
480 volts.
Alternating current.
They must be installed at least 7 feet above the ground.

5. What type of 3-phase AC motor is used most often around a mine?
A device used to store electrical energy.
Squirrel-cage induction motor.
Four times less than that of the secondary.
Full-load - three-phase voltage.

6. Not true about AC power?
It provides good speed control.
15 feet off the ground.
Zero amps.
The sum of the two capacitors.

7. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
277 volts.
Transformers.
Two speeds
Electro-magnetism for their operation.

8. 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.
Shunted and taped
The sum of the two capacitors.
Cut around clothing that has adhered to the burned area.

9. Not a symptom of electrical shock?.
Derive a neutral for grounding purposes.
H terminals.
Hyperventilation.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

10. A transformer with a 1:1 ratio is usually a (an)...
Check to make sure that the victim is not still in contact with the electricity.
A device used to store electrical energy.
7 -630 volts.
Isolation transformer.

11. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
7 -630 volts.
Circuit Breaker.
600 volts.

12. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Continuous.
Short-circuited after power has been removed.
Circuit Breaker.
A.C.

13. A burn causing a blister is classified as a...
A grounding resistor.
12 to 15 times a minute.
Reverse any two-phase leads.
Second-degree burn.

14. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Capacitance.
A step-up transformer.
Nearly constant.

15. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Because less current flowing at high voltage causes less line loss per kilowatt.
60 Hertz
The sum of the two capacitors.
A step-up transformer.

16. The standard frequency of alternating current used at a mine is...
480 volts.
60 Hertz
2000 watts
A step-up transformer.

17. A control power transformer...
No.6 AWG.
Grounded phase and ground fault devices were not operating.
150 turns.
Provides single-phase power to smaller loads such as lights - heaters - etc.

18. All transformers step voltage up or down by...
Check to make sure that the victim is not still in contact with the electricity.
Inductance.
200 volts AC.
60 Hertz

19. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Draw less current.
No.6 AWG.
2000 watts

20. 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.
100 volts.
277 volts.
3 -979 Volts.

21. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
H terminals.
Potential transformer.
No.6 AWG.

22. What type motor is a wound-rotor induction motor?
A.C.
100 turns.
Full-load - three-phase voltage.
A step-up transformer.

23. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Because less current flowing at high voltage causes less line loss per kilowatt.
3 -979 Volts.
Disconnect the frame-grounding conductor.
A step-up transformer.

24. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Grounded phase and ground fault devices were not operating.
The sum of the two capacitors.
The current will read zero.
480 volts.

25. Compared to the secondary of a loaded - step-down transformer - the primary has...
H terminals.
No.6 AWG.
Lower current and higher voltage.
15 feet off the ground.

26. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Check to make sure that the victim is not still in contact with the electricity.
They must be installed at least 7 feet above the ground.
Zero amps.

27. At what rate should mouth-to-mouth resuscitation be applied?
At least two phases
150 turns.
Disconnect the frame-grounding conductor.
12 to 15 times a minute.

28. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Isolation transformer.
15 feet off the ground.
The motor rotation is reversed.
5:1.

29. Which of the following does a squirrel cage induction motor have?
The current will read zero.
5:1
150 turns.
Stator windings.

30. 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...
7 -630 volts.
The chest should rise or inflate.
Draw less current.
Circuit Breaker.

31. 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?
Full-load - three-phase voltage.
Reverse its rotation.
The sum of the two capacitors.
3 -979 Volts.

32. Three-phase AC underground cables must be provided with overcurrent protection using a...
Short-circuited after power has been removed.
Transformer
Circuit Breaker.
X.

33. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
At the source transformer.
Isolation transformer.
X.
100 turns.

34. A wound-rotor induction motor has all the following EXCEPT...
The current will read zero.
The capacitors should be discharged.
Squirrel-cage rotor.
The motor rotation is reversed.

35. What is a capacitor?
Carotid pulse - which is located in the neck next to the Adam's apple.
A device used to store electrical energy.
Zero amps.
3 -979 Volts.

36. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
3 -979 Volts.
Capacitance.
Squirrel-cage rotor.
2000 watts

37. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Short-circuited after power has been removed.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
200 volts AC.

38. A solenoid coil is...
60 Hertz
15 feet off the ground.
An electromagnet.
25 feet.

39. The property of an electrical circuit that opposes any change in voltage is called...
600 volts.
100 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Capacitance.

40. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Isolation transformer.
200 volts AC.
7 -630 volts.
At the source transformer.

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

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42. 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...
Potential transformer.
Draw less current.
5:1
Stator windings.

43. 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.
Cut around clothing that has adhered to the burned area.
800 volts.
277 volts.

44. 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?
200 volts AC.
Transformers.
480 volts.
800 volts.

45. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
2000 watts
Four times less than that of the secondary.
Tied together

46. What is the first step to be followed in aiding a victim of electrical shock?
60 cycles per second (60 Hertz).
100 turns.
Check to make sure that the victim is not still in contact with the electricity.
150 turns.

47. Current that changes periodically in direction is...
Alternating current.
Second-degree burn.
Stator windings.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

48. What is the danger when working around capacitors?
An electrical shock hazard may exist.
277 volts.
100 turns.
Isolation transformer.

49. What should the duty rating of a grounding resistor be?
Continuous.
100 volts.
Clamp-on ammeter.
15 feet off the ground.

50. 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?
Stator windings.
Grounded phase and ground fault devices were not operating.
Disconnect the frame-grounding conductor.
150 turns.

Can you answer 50 questions in 15 minutes?

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AC Theory

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