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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. Not a symptom of electrical shock?.
75 turns.
Hyperventilation.
Cut around clothing that has adhered to the burned area.
An electromagnet.

2. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
A device used to store electrical energy.
At the source transformer.
Short-circuited after power has been removed.
The motor rotation is reversed.

3. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Potential transformer.
Short-circuited after power has been removed.
H terminals.

4. 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?
3 -979 Volts.
Inductance.
Inductance.
200 volts AC.

5. 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...
Check to make sure that the victim is not still in contact with the electricity.
No.6 AWG.
Draw less current.
Zero amps.

6. 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.
5:1.
Two speeds
Clamp-on ammeter.
Electro-magnetism for their operation.

7. How do you change the direction of a 3-phase AC motor?
The chest should rise or inflate.
Current that changes constantly in magnitude and periodically in direction.
Reverse any two-phase leads.
15 feet off the ground.

8. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Potential transformer.
A.C.
A step-up transformer.
An electrical shock hazard may exist.

9. How should clothing be removed from a burn?
Derive a neutral for grounding purposes.
Cut around clothing that has adhered to the burned area.
Short-circuited after power has been removed.
No.6 AWG.

10. Current that changes periodically in direction is...
Squirrel-cage rotor.
Alternating current.
100 turns.
At the source transformer.

11. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Circuit Breaker.
A step-up transformer.
800 volts.

12. Current transformers - or CT's - are used to...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The sum of the two capacitors.
Short-circuited after power has been removed.

13. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
No.6 AWG.
75 turns.
Capacitance.
2000 watts

14. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
The current will read zero.
The motor rotation is reversed.
They should be made by the same manufacturer.

15. 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...
75 turns.
100 volts.
Check to make sure that the victim is not still in contact with the electricity.
Second-degree burn.

16. When not connected to a load - the secondary leads of a current transformer should be...
Reverse any two-phase leads.
Cut around clothing that has adhered to the burned area.
Shunted and taped
Check to make sure that the victim is not still in contact with the electricity.

17. The purpose of a zig-zag transformer is to...
Hyperventilation.
3 -979 Volts.
An electromagnet.
Derive a neutral for grounding purposes.

18. The main function of CT's and PT's on a main substation is to...
Circuit Breaker.
150 turns.
Allow for metering voltage and Current.
Lower current and higher voltage.

19. What is a capacitor?
A device used to store electrical energy.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Larger than that found in the primary winding.
Lower current and higher voltage.

20. The speed of an alternating current - squirrel-cage induction motor is...
100 volts.
A grounding resistor.
Nearly constant.
3 -979 Volts.

21. 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?
At least two phases
An electrical shock hazard may exist.
75 turns.
Inductance.

22. Three-phase AC underground cables must be provided with overcurrent protection using a...
60 cycles per second (60 Hertz).
Circuit Breaker.
5:1
Squirrel-cage rotor.

23. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
The capacitors should be discharged.
Reverse its rotation.
A grounding resistor.
5:1

24. What is the danger when working around capacitors?
Disconnect the frame-grounding conductor.
The chest should rise or inflate.
Allow for metering voltage and Current.
An electrical shock hazard may exist.

25. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Kilovolt ampere (KVA).
Squirrel-cage rotor.
Reverse any two-phase leads.
Disconnect the frame-grounding conductor.

26. A burn causing a blister is classified as a...
Electro-magnetism for their operation.
Transformers.
Second-degree burn.
It provides good speed control.

27. 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.
Stator windings.
They should be made by the same manufacturer.
Transformers.

28. The combined capacitance of two capacitors in parallel is...
277 volts.
Disconnect the frame-grounding conductor.
Two speeds
The sum of the two capacitors.

29. Define alternating current...
5:1.
Current changing constantly in magnitude and periodically in direction.
At the source transformer.
Short-circuited after power has been removed.

30. Alternating current may be defined as...
480 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Current that changes constantly in magnitude and periodically in direction.
Two speeds

31. What type motor is a wound-rotor induction motor?
A.C.
25 feet.
Alternating current.
5:1

32. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Derive a neutral for grounding purposes.
The chest should rise or inflate.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Draw less current.

33. What type of 3-phase AC motor is used most often around a mine?
The chest should rise or inflate.
Squirrel-cage induction motor.
They must be installed at least 7 feet above the ground.
The motor rotation is reversed.

34. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
600 volts.
Four times less than that of the secondary.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Grounded phase and ground fault devices were not operating.

35. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Alternating current.
15 feet off the ground.
3 -979 Volts.
Reverse its rotation.

36. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
100 volts.
No.6 AWG.
At the source transformer.

37. The size of a transformer is measured in...
Derive a neutral for grounding purposes.
60 cycles per second (60 Hertz).
Squirrel-cage induction motor.
Kilovolt ampere (KVA).

38. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
75 turns.
Two speeds
The motor rotation is reversed.
H terminals.

39. The primary function of a power transformer is to provide...
600 volts.
Full-load - three-phase voltage.
Transformers.
Zero amps.

40. AC voltage is raised or lowered by means of...
At the source transformer.
Transformers.
Cut around clothing that has adhered to the burned area.
Provides single-phase power to smaller loads such as lights - heaters - etc.

41. The property of an electrical circuit that opposes any change in voltage is called...
It provides good speed control.
The chest should rise or inflate.
Capacitance.
Tied together

42. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
It provides good speed control.
Provides single-phase power to smaller loads such as lights - heaters - etc.
200 volts AC.

43. Which of the following does a squirrel cage induction motor have?
The current will read zero.
3 -979 Volts.
Stator windings.
X.

44. Compared to the secondary of a loaded - step-down transformer - the primary has...
Hyperventilation.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Lower current and higher voltage
The current will read zero.

45. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Because less current flowing at high voltage causes less line loss per kilowatt.
Stator windings.
They should be made by the same manufacturer.
Current changing constantly in magnitude and periodically in direction.

46. A wound-rotor induction motor has all the following EXCEPT...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Squirrel-cage rotor.
Disconnect the frame-grounding conductor.
X.

47. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
75 turns.
Full-load - three-phase voltage.
Grounded phase and ground fault devices were not operating.
No.6 AWG.

48. A transformer with a 1:1 ratio is usually a (an)...
600 volts.
No.6 AWG.
Isolation transformer.
7 -630 volts.

49. 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.
Transformer
A grounding resistor.
5:1
At least two phases

50. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
3 -979 Volts.
Kilovolt ampere (KVA).
They should be made by the same manufacturer.