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 is the danger when working around capacitors?
Electro-magnetism for their operation.
Derive a neutral for grounding purposes.
An electrical shock hazard may exist.
A device used to store electrical energy.

2. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Check to make sure that the victim is not still in contact with the electricity.
The current will read zero.
75 turns.
At least two phases

3. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
277 volts.
Draw less current.
Stator windings.
7 -630 volts.

4. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
100 volts.
At the source transformer.
Grounded phase and ground fault devices were not operating.
Two speeds

5. The standard frequency of alternating current used at a mine is...
800 volts.
1 amp.
60 Hertz
60 cycles per second (60 Hertz).

6. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
100 volts.
Lower current and higher voltage.
Clamp-on ammeter.

7. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
No.6 AWG.
Tied together
H terminals.

8. 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.
75 turns.
Tied together
100 volts.

9. 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?
480 volts.
Squirrel-cage induction motor.
X.
200 volts AC.

10. A control power transformer...
An electromagnet.
A grounding resistor.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Larger than that found in the primary winding.

11. What is a capacitor?
Inductance.
15 feet off the ground.
Two speeds
A device used to store electrical energy.

12. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
The motor rotation is reversed.
25 feet.
Full-load - three-phase voltage.
480 volts.

13. What is the first step to be followed in aiding a victim of electrical shock?
Continuous.
75 turns.
Check to make sure that the victim is not still in contact with the electricity.
Inductance.

14. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
3 -979 Volts.
Inductance.
1 amp.
Shunted and taped

15. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Second-degree burn.
15 feet off the ground.
Hyperventilation.
5:1

16. 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...
100 volts.
60 cycles per second (60 Hertz).
Provides single-phase power to smaller loads such as lights - heaters - etc.
15 feet off the ground.

17. What steps up or steps down AC voltage?
Transformer
Short-circuited after power has been removed.
At least two phases
A step-up transformer.

18. If any two-phase wires are reversed on a three-phase motor - the motor will...
60 Hertz
The sum of the two capacitors.
Reverse its rotation.
Current that changes constantly in magnitude and periodically in direction.

19. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Current that changes constantly in magnitude and periodically in direction.
Squirrel-cage rotor.
The current will read zero.
Lower current and higher voltage.

20. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Alternating current.
Derive a neutral for grounding purposes.
They must be installed at least 7 feet above the ground.

21. The secondary windings on a 10:1 step-down transformer will have a wire size...
2000 watts
Larger than that found in the primary winding.
480 volts.
A.C.

22. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
A grounding resistor.
Transformers.
Shunted and taped

23. At what rate should mouth-to-mouth resuscitation be applied?
Inductance.
12 to 15 times a minute.
Carotid pulse - which is located in the neck next to the Adam's apple.
Short-circuited after power has been removed.

24. 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.
X.
Isolation transformer.
75 turns.

25. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Circuit Breaker.
Second-degree burn.
Two speeds
Four times less than that of the secondary.

26. 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?
At the source transformer.
Circuit Breaker.
150 turns.
Capacitance.

27. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
The current will read zero.
Draw less current.
800 volts.

28. 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...
Draw less current.
Kilovolt ampere (KVA).
Hyperventilation.
They must be installed at least 7 feet above the ground.

29. Operating coils - motors - transformers - relays and solenoids depend upon...
Draw less current.
Electro-magnetism for their operation.
A grounding resistor.
Capacitance.

30. Where should grounding resistors be located?
60 Hertz
480 volts.
At the source transformer.
A.C.

31. What should the duty rating of a grounding resistor be?
Continuous.
A device used to store electrical energy.
60 cycles per second (60 Hertz).
Isolation transformer.

32. 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?
Shunted and taped
100 turns.
The motor rotation is reversed.
75 turns.

33. 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?
Inductance.
Squirrel-cage rotor.
Shunted and taped
3 -979 Volts.

34. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
150 turns.
They must be installed at least 7 feet above the ground.
Draw less current.

35. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Clamp-on ammeter.
A step-up transformer.
60 Hertz
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

36. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
600 volts.
No.6 AWG.
Check to make sure that the victim is not still in contact with the electricity.
A grounding resistor.

37. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Alternating current.
Check to make sure that the victim is not still in contact with the electricity.
The current will read zero.
Disconnect the frame-grounding conductor.

38. Not true about AC power?
15 feet off the ground.
Clamp-on ammeter.
It provides good speed control.
Grounded phase and ground fault devices were not operating.

39. The transformer used only to measure voltage is a...
Squirrel-cage induction motor.
Draw less current.
Potential transformer.
Allow for metering voltage and Current.

40. A wound-rotor induction motor has all the following EXCEPT...
Transformer
Squirrel-cage rotor.
150 turns.
Short-circuited after power has been removed.

41. Define alternating current...
25 feet.
An electrical shock hazard may exist.
1 amp.
Current changing constantly in magnitude and periodically in direction.

42. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The motor rotation is reversed.
150 turns.
The chest should rise or inflate.
3 -979 Volts.

43. The speed of an alternating current - squirrel-cage induction motor is...
A grounding resistor.
200 volts AC.
277 volts.
Nearly constant.

44. AC voltage is raised or lowered by means of...
At the source transformer.
15 feet off the ground.
Hyperventilation.
Transformers.

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...
Second-degree burn.
Draw less current.
Cut around clothing that has adhered to the burned area.
60 Hertz

46. Current in an AC circuit may be measured by...
At least two phases
Squirrel-cage induction motor.
Clamp-on ammeter.
Stator windings.

47. What type of 3-phase AC motor is used most often around a mine?
2000 watts
Squirrel-cage induction motor.
A.C.
Two speeds

48. All transformers step voltage up or down by...
Inductance.
Reverse its rotation.
75 turns.
Current that changes constantly in magnitude and periodically in direction.

49. How should clothing be removed from a burn?
Shunted and taped
Squirrel-cage induction motor.
Cut around clothing that has adhered to the burned area.
15 feet off the ground.

50. Which of the following does a squirrel cage induction motor have?
Hyperventilation.
Carotid pulse - which is located in the neck next to the Adam's apple.
Disconnect the frame-grounding conductor.
Stator windings.