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Test your basic knowledge |

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. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
150 turns.
Transformers.
Disconnect the frame-grounding conductor.
The motor rotation is reversed.

2. 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.
Derive a neutral for grounding purposes.
800 volts.
Two speeds

3. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
100 turns.
H terminals.
7 -630 volts.
2000 watts

4. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
It provides good speed control.
Lower current and higher voltage.
5:1.

5. The standard frequency of power supplied by the power company is...
75 turns.
Squirrel-cage rotor.
Inductance.
60 cycles per second (60 Hertz).

6. 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...
It provides good speed control.
100 volts.
60 Hertz
Clamp-on ammeter.

7. The transformer used only to measure voltage is a...
Potential transformer.
The sum of the two capacitors.
Draw less current.
The capacitors should be discharged.

8. Where should grounding resistors be located?
2000 watts
Draw less current.
Current changing constantly in magnitude and periodically in direction.
At the source transformer.

9. Which of the following does a squirrel cage induction motor have?
At least two phases
3 -979 Volts.
Squirrel-cage induction motor.
Stator windings.

10. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Lower current and higher voltage.
Shunted and taped
It provides good speed control.

11. How do you change the direction of a 3-phase AC motor?
Electro-magnetism for their operation.
Circuit Breaker.
Reverse any two-phase leads.
Carotid pulse - which is located in the neck next to the Adam's apple.

12. A solenoid coil is...
Two speeds
An electrical shock hazard may exist.
Shunted and taped
An electromagnet.

13. AC voltage is raised or lowered by means of...
Because less current flowing at high voltage causes less line loss per kilowatt.
The sum of the two capacitors.
Transformer
Transformers.

14. 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...
A device used to store electrical energy.
Because less current flowing at high voltage causes less line loss per kilowatt.
Draw less current.
Cut around clothing that has adhered to the burned area.

15. Alternating current may be defined as...
75 turns.
150 turns.
At least two phases
Current that changes constantly in magnitude and periodically in direction.

16. The purpose of a zig-zag transformer is to...
60 Hertz
Derive a neutral for grounding purposes.
7 -630 volts.
277 volts.

17. 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.
60 cycles per second (60 Hertz).
The sum of the two capacitors.
The chest should rise or inflate.

18. The primary leads of a single-phase transformer should be connected to the...
H terminals.
600 volts.
3 -979 Volts.
Circuit Breaker.

19. What is the first step to be followed in aiding a victim of electrical shock?
Carotid pulse - which is located in the neck next to the Adam's apple.
Lower current and higher voltage.
Draw less current.
Check to make sure that the victim is not still in contact with the electricity.

20. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Electro-magnetism for their operation.
No.6 AWG.
H terminals.
Disconnect the frame-grounding conductor.

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

22. Three-phase AC underground cables must be provided with overcurrent protection using a...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Circuit Breaker.
X.
5:1

23. What type of 3-phase AC motor is used most often around a mine?
Hyperventilation.
25 feet.
Allow for metering voltage and Current.
Squirrel-cage induction motor.

24. 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?
Potential transformer.
The chest should rise or inflate.
At the source transformer.
3 -979 Volts.

25. The main function of CT's and PT's on a main substation is to...
An electromagnet.
Two speeds
Allow for metering voltage and Current.
H terminals.

26. At what rate should mouth-to-mouth resuscitation be applied?
Four times less than that of the secondary.
Carotid pulse - which is located in the neck next to the Adam's apple.
A device used to store electrical energy.
12 to 15 times a minute.

27. 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...
60 cycles per second (60 Hertz).
Tied together
Draw less current.
An electromagnet.

28. What is the danger when working around capacitors?
75 turns.
An electrical shock hazard may exist.
Draw less current.
Hyperventilation.

29. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
A.C.
An electromagnet.
Provides single-phase power to smaller loads such as lights - heaters - etc.

30. Compared to the secondary of a loaded - step-down transformer - the primary has...
The current will read zero.
277 volts.
H terminals.
Lower current and higher voltage

31. What steps up or steps down AC voltage?
Transformer
The current will read zero.
100 volts.
Two speeds

32. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
At the source transformer.
1 amp.
An electromagnet.
15 feet off the ground.

33. Current in an AC circuit may be measured by...
Transformers.
Clamp-on ammeter.
800 volts.
200 volts AC.

34. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
An electrical shock hazard may exist.
480 volts.
Larger than that found in the primary winding.
100 volts.

35. A burn causing a blister is classified as a...
Second-degree burn.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Inductance.
Reverse any two-phase leads.

36. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
1 amp.
H terminals.
Draw less current.

37. What type motor is a wound-rotor induction motor?
A.C.
The motor rotation is reversed.
Reverse any two-phase leads.
Zero amps.

38. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Transformers.
The sum of the two capacitors.
100 turns.
Disconnect the frame-grounding conductor.

39. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.
Squirrel-cage rotor.
100 turns.

40. 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.
Disconnect the frame-grounding conductor.
60 Hertz
Draw less current.

41. Not a symptom of electrical shock?.
25 feet.
It provides good speed control.
Tied together
Hyperventilation.

42. The speed of an alternating current - squirrel-cage induction motor is...
Current changing constantly in magnitude and periodically in direction.
Nearly constant.
1 amp.
Electro-magnetism for their operation.

43. The property of an electrical circuit that opposes any change in voltage is called...
It provides good speed control.
Capacitance.
200 volts AC.
The chest should rise or inflate.

44. When not connected to a load - the secondary leads of a current transformer should be...
Nearly constant.
Shunted and taped
277 volts.
An electromagnet.

45. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
The capacitors should be discharged.
X.
Nearly constant.
Continuous.

46. Compared to the secondary of a loaded - step-down transformer - the primary has...
480 volts.
1 amp.
60 cycles per second (60 Hertz).
Lower current and higher voltage.

47. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
It provides good speed control.
Carotid pulse - which is located in the neck next to the Adam's apple.
A step-up transformer.
Four times less than that of the secondary.

48. A control power transformer...
Potential transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
A step-up transformer.
The sum of the two capacitors.

49. What is a capacitor?
75 turns.
75 turns.
Zero amps.
A device used to store electrical energy.

50. 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?
Transformer
75 turns.
The sum of the two capacitors.
600 volts.