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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. 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?
Reverse its rotation.
75 turns.
Larger than that found in the primary winding.
Electro-magnetism for their operation.

2. The property of an electric circuit that opposes any change in current is called...
Inductance.
Circuit Breaker.
The sum of the two capacitors.
Current that changes constantly in magnitude and periodically in direction.

3. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The current will read zero.
277 volts.
75 turns.
A step-up transformer.

4. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
They should be made by the same manufacturer.
The current will read zero.
Potential transformer.

5. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
5:1
Disconnect the frame-grounding conductor.
X.

6. At what rate should mouth-to-mouth resuscitation be applied?
Reverse its rotation.
12 to 15 times a minute.
Transformer
5:1

7. What should the duty rating of a grounding resistor be?
An electromagnet.
Continuous.
The motor rotation is reversed.
100 volts.

8. 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...
15 feet off the ground.
Hyperventilation.
60 cycles per second (60 Hertz).
Draw less current.

9. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
7 -630 volts.
2000 watts
Disconnect the frame-grounding conductor.
Check to make sure that the victim is not still in contact with the electricity.

10. 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?
60 Hertz
Carotid pulse - which is located in the neck next to the Adam's apple.
The current will read zero.
150 turns.

11. The primary function of a power transformer is to provide...
At least two phases
Full-load - three-phase voltage.
The capacitors should be discharged.
Hyperventilation.

12. The speed of an alternating current - squirrel-cage induction motor is...
Grounded phase and ground fault devices were not operating.
Nearly constant.
Derive a neutral for grounding purposes.
An electrical shock hazard may exist.

13. Which of the following does a squirrel cage induction motor have?
Stator windings.
Draw less current.
Lower current and higher voltage.
Two speeds

14. 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.
Draw less current.
Reverse any two-phase leads.
Carotid pulse - which is located in the neck next to the Adam's apple.

15. Operating coils - motors - transformers - relays and solenoids depend upon...
Capacitance.
Grounded phase and ground fault devices were not operating.
Draw less current.
Electro-magnetism for their operation.

16. AC voltage is raised or lowered by means of...
Full-load - three-phase voltage.
Transformers.
800 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

17. What is the first step to be followed in aiding a victim of electrical shock?
75 turns.
They must be installed at least 7 feet above the ground.
Check to make sure that the victim is not still in contact with the electricity.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

18. Where should grounding resistors be located?
The capacitors should be discharged.
Reverse its rotation.
Cut around clothing that has adhered to the burned area.
At the source transformer.

19. High voltage is used to transmit power over long distances...
1 amp.
Inductance.
Because less current flowing at high voltage causes less line loss per kilowatt.
Draw less current.

20. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Allow for metering voltage and Current.
Larger than that found in the primary winding.
Shunted and taped
A step-up transformer.

21. When not connected to a load - the secondary leads of a current transformer should be...
Nearly constant.
Short-circuited after power has been removed.
277 volts.
Shunted and taped

22. What is the danger when working around capacitors?
Hyperventilation.
They must be installed at least 7 feet above the ground.
An electrical shock hazard may exist.
They should be made by the same manufacturer.

23. The transformer used only to measure voltage is a...
Potential transformer.
A device used to store electrical energy.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Reverse its rotation.

24. A transformer with a 1:1 ratio is usually a (an)...
They must be installed at least 7 feet above the ground.
A grounding resistor.
Allow for metering voltage and Current.
Isolation transformer.

25. The secondary windings on a 10:1 step-down transformer will have a wire size...
Tied together
Nearly constant.
Larger than that found in the primary winding.
Reverse any two-phase leads.

26. Alternating current may be defined as...
Continuous.
Allow for metering voltage and Current.
Current that changes constantly in magnitude and periodically in direction.
The capacitors should be discharged.

27. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Transformer
Zero amps.
600 volts.

28. What type motor is a wound-rotor induction motor?
A.C.
Current that changes constantly in magnitude and periodically in direction.
Hyperventilation.
Transformer

29. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
800 volts.
X.
Four times less than that of the secondary.
Continuous.

30. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Tied together
3 -979 Volts.
Short-circuited after power has been removed.

31. 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.
Lower current and higher voltage.
Draw less current.
Kilovolt ampere (KVA).

32. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Nearly constant.
H terminals.
Inductance.
7 -630 volts.

33. What type of 3-phase AC motor is used most often around a mine?
5:1
Squirrel-cage induction motor.
5:1.
At the source transformer.

34. 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?
7 -630 volts.
H terminals.
100 volts.
100 turns.

35. Define alternating current...
75 turns.
Second-degree burn.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Current changing constantly in magnitude and periodically in direction.

36. The standard frequency of alternating current used at a mine is...
Zero amps.
The motor rotation is reversed.
5:1.
60 Hertz

37. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
No.6 AWG.
15 feet off the ground.
Electro-magnetism for their operation.
277 volts.

38. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
A grounding resistor.
No.6 AWG.
Derive a neutral for grounding purposes.
The sum of the two capacitors.

39. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
800 volts.
No.6 AWG.
Transformer
Zero amps.

40. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
A grounding resistor.
150 turns.
3 -979 Volts.

41. 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?
Provides single-phase power to smaller loads such as lights - heaters - etc.
600 volts.
100 turns.
5:1.

42. Compared to the secondary of a loaded - step-down transformer - the primary has...
X.
Lower current and higher voltage
Two speeds
Derive a neutral for grounding purposes.

43. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
X.
Continuous.
Squirrel-cage induction motor.

44. The combined capacitance of two capacitors in parallel is...
600 volts.
The sum of the two capacitors.
Because less current flowing at high voltage causes less line loss per kilowatt.
Short-circuited after power has been removed.

45. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
100 turns.
60 cycles per second (60 Hertz).
15 feet off the ground.
600 volts.

46. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Inductance.
The motor rotation is reversed.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

47. Three-phase AC underground cables must be provided with overcurrent protection using a...
Alternating current.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Circuit Breaker.
Current that changes constantly in magnitude and periodically in direction.

48. Not true about AC power?
It provides good speed control.
Transformers.
480 volts.
75 turns.

49. All transformers step voltage up or down by...
Lower current and higher voltage.
Reverse any two-phase leads.
Inductance.
Larger than that found in the primary winding.

50. Not a symptom of electrical shock?.
25 feet.
Disconnect the frame-grounding conductor.
Hyperventilation.
Short-circuited after power has been removed.