Test your basic knowledge |

AC Theory

Instructions:

Answer 50 questions in 15 minutes. 2 minutes extra for reading the instructions.
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 burn causing a blister is classified as a...
At the source transformer.
Two speeds
A device used to store electrical energy.
Second-degree burn.

2. Find the turns ratio of a single-phase transformer with the following values: Primary power of 10 KW - secondary current of 200 amps - and primary voltage of 250 volts.
Full-load - three-phase voltage.
5:1.
Nearly constant.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

3. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Inductance.
Larger than that found in the primary winding.
The motor rotation is reversed.
75 turns.

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

5. The primary function of a power transformer is to provide...
A device used to store electrical energy.
Allow for metering voltage and Current.
Full-load - three-phase voltage.
The capacitors should be discharged.

6. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Current that changes constantly in magnitude and periodically in direction.
100 turns.
They should be made by the same manufacturer.
Grounded phase and ground fault devices were not operating.

7. The primary leads of a single-phase transformer should be connected to the...
600 volts.
Larger than that found in the primary winding.
H terminals.
Reverse its rotation.

8. What type motor is a wound-rotor induction motor?
Current that changes constantly in magnitude and periodically in direction.
A.C.
12 to 15 times a minute.
The current will read zero.

9. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Squirrel-cage induction motor.
480 volts.
Reverse its rotation.
Derive a neutral for grounding purposes.

10. What is a capacitor?
A device used to store electrical energy.
Transformer
Reverse its rotation.
Draw less current.

11. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Lower current and higher voltage.
The sum of the two capacitors.
277 volts.
The chest should rise or inflate.

12. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Short-circuited after power has been removed.
25 feet.
Zero amps.
15 feet off the ground.

13. A solenoid coil is...
Nearly constant.
Current that changes constantly in magnitude and periodically in direction.
Tied together
An electromagnet.

14. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Grounded phase and ground fault devices were not operating.
Zero amps.
An electrical shock hazard may exist.
No.6 AWG.

15. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Hyperventilation.
100 volts.
Check to make sure that the victim is not still in contact with the electricity.

16. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
Nearly constant.
800 volts.
Clamp-on ammeter.

17. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Shunted and taped
Continuous.
Short-circuited after power has been removed.
Clamp-on ammeter.

18. Current in an AC circuit may be measured by...
Grounded phase and ground fault devices were not operating.
Full-load - three-phase voltage.
15 feet off the ground.
Clamp-on ammeter.

19. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
15 feet off the ground.
Isolation transformer.
7 -630 volts.
Nearly constant.

20. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
At least two phases
800 volts.
A device used to store electrical energy.
The capacitors should be discharged.

21. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Shunted and taped
600 volts.

22. Not a symptom of electrical shock?.
Capacitance.
Hyperventilation.
Lower current and higher voltage.
They should be made by the same manufacturer.

23. 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...
2000 watts
No.6 AWG.
At least two phases
Draw less current.

24. 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?
Check to make sure that the victim is not still in contact with the electricity.
25 feet.
600 volts.
480 volts.

25. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
An electromagnet.
Transformers.
Current changing constantly in magnitude and periodically in direction.
Four times less than that of the secondary.

26. The property of an electric circuit that opposes any change in current is called...
Inductance.
Draw less current.
25 feet.
480 volts.

27. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Nearly constant.
They must be installed at least 7 feet above the ground.
15 feet off the ground.

28. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
X.
A.C.
480 volts.
15 feet off the ground.

29. Not true about AC power?
Circuit Breaker.
Isolation transformer.
It provides good speed control.
They must be installed at least 7 feet above the ground.

30. The transformer used only to measure voltage is a...
277 volts.
Potential transformer.
Grounded phase and ground fault devices were not operating.
Capacitance.

31. The purpose of a zig-zag transformer is to...
The motor rotation is reversed.
Hyperventilation.
The capacitors should be discharged.
Derive a neutral for grounding purposes.

32. The main function of CT's and PT's on a main substation is to...
Two speeds
Allow for metering voltage and Current.
Electro-magnetism for their operation.
Capacitance.

33. When not connected to a load - the secondary leads of a current transformer should be...
75 turns.
A device used to store electrical energy.
The sum of the two capacitors.
Shunted and taped

34. Which of the following does a squirrel cage induction motor have?
Transformer
Derive a neutral for grounding purposes.
25 feet.
Stator windings.

35. Find the turns ratio of a single-phase transformer with the following values: Primary power of 5KW - secondary current of 100 amps - and primary voltage of 250 volts.
A step-up transformer.
Second-degree burn.
5:1
Draw less current.

36. Where should grounding resistors be located?
Allow for metering voltage and Current.
Carotid pulse - which is located in the neck next to the Adam's apple.
Four times less than that of the secondary.
At the source transformer.

37. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
1 amp.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
At least two phases
An electromagnet.

38. 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
Disconnect the frame-grounding conductor.
60 cycles per second (60 Hertz).
15 feet off the ground.

39. What is the first step to be followed in aiding a victim of electrical shock?
15 feet off the ground.
Because less current flowing at high voltage causes less line loss per kilowatt.
Check to make sure that the victim is not still in contact with the electricity.
75 turns.

40. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
2000 watts
An electrical shock hazard may exist.
Clamp-on ammeter.

41. 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?
150 turns.
They must be installed at least 7 feet above the ground.
Circuit Breaker.
A step-up transformer.

42. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Continuous.
Hyperventilation.
60 Hertz

43. 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?
3 -979 Volts.
The current will read zero.
An electromagnet.
Squirrel-cage induction motor.

44. A wound-rotor induction motor has all the following EXCEPT...
Shunted and taped
277 volts.
Squirrel-cage rotor.
Capacitance.

45. 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...
Draw less current.
Circuit Breaker.
Electro-magnetism for their operation.
Stator windings.

46. The standard frequency of alternating current used at a mine is...
800 volts.
60 Hertz
Capacitance.
No.6 AWG.

47. Current that changes periodically in direction is...
100 volts.
Alternating current.
Electro-magnetism for their operation.
The capacitors should be discharged.

48. What type of 3-phase AC motor is used most often around a mine?
H terminals.
Draw less current.
Potential transformer.
Squirrel-cage induction motor.

49. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
75 turns.
1 amp.
60 cycles per second (60 Hertz).

50. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
480 volts.
Grounded phase and ground fault devices were not operating.
60 Hertz

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Test your basic knowledge |

AC Theory

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3d Computer Modeling

Actionscript

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Adobe Illustrator Shortcuts

Adobe Indesign Publishing

Adobe Photoshop CS 2 - CS 3

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Adobe Photoshop CS 5 Keyboard Shortcuts

Adobe Photoshop Graphic Design

Adobe Photoshop Tools And Commands

Adobe Premiere Keyboard Shortcuts

Adobe Premiere Pro

After Effects Keyboard Shortcuts

Agile Development

Agile Scrum Methodology

Ajax

Android Programming

Animation

Asp.net Programming