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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. The main function of CT's and PT's on a main substation is to...
A device used to store electrical energy.
60 Hertz
Hyperventilation.
Allow for metering voltage and Current.

2. AC voltage is raised or lowered by means of...
X.
Hyperventilation.
Transformers.
They must be installed at least 7 feet above the ground.

3. Which of the following does a squirrel cage induction motor have?
2000 watts
Stator windings.
Current changing constantly in magnitude and periodically in direction.
Larger than that found in the primary winding.

4. A burn causing a blister is classified as a...
15 feet off the ground.
Squirrel-cage rotor.
1 amp.
Second-degree burn.

5. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Larger than that found in the primary winding.
A device used to store electrical energy.
277 volts.
Current changing constantly in magnitude and periodically in direction.

6. The property of an electric circuit that opposes any change in current is called...
Inductance.
75 turns.
200 volts AC.
Lower current and higher voltage.

7. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Short-circuited after power has been removed.
They should be made by the same manufacturer.
150 turns.
Draw less current.

8. 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.
Current that changes constantly in magnitude and periodically in direction.
A.C.
5:1
Transformers.

9. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
25 feet.
150 turns.
A grounding resistor.

10. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
At least two phases
Continuous.
Second-degree burn.
No.6 AWG.

11. Not a symptom of electrical shock?.
Hyperventilation.
Lower current and higher voltage
A.C.
Transformer

12. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Current changing constantly in magnitude and periodically in direction.
Larger than that found in the primary winding.
The sum of the two capacitors.
A grounding resistor.

13. All transformers step voltage up or down by...
Inductance.
150 turns.
They should be made by the same manufacturer.
5:1

14. 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...
Derive a neutral for grounding purposes.
Tied together
Transformers.
Clamp-on ammeter.

15. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Clamp-on ammeter.
Derive a neutral for grounding purposes.
X.

16. A transformer has 2000 turns in the primary and 500 turns in the secondary. The primary voltage is 3 -200 volts. What is the secondary voltage?
A.C.
5:1.
800 volts.
Inductance.

17. Operating coils - motors - transformers - relays and solenoids depend upon...
Lower current and higher voltage.
Electro-magnetism for their operation.
Grounded phase and ground fault devices were not operating.
Hyperventilation.

18. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Draw less current.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
200 volts AC.
Lower current and higher voltage.

19. High voltage is used to transmit power over long distances...
H terminals.
They must be installed at least 7 feet above the ground.
Larger than that found in the primary winding.
Because less current flowing at high voltage causes less line loss per kilowatt.

20. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Inductance.
Shunted and taped
5:1

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

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22. Not true about AC power?
200 volts AC.
Capacitance.
Current changing constantly in magnitude and periodically in direction.
It provides good speed control.

23. 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.
100 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
800 volts.

24. 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?
75 turns.
Capacitance.
150 turns.
5:1.

25. What type motor is a wound-rotor induction motor?
A.C.
The chest should rise or inflate.
An electrical shock hazard may exist.
Inductance.

26. Define alternating current...
75 turns.
Current changing constantly in magnitude and periodically in direction.
Larger than that found in the primary winding.
600 volts.

27. A control power transformer...
60 cycles per second (60 Hertz).
Kilovolt ampere (KVA).
Squirrel-cage induction motor.
Provides single-phase power to smaller loads such as lights - heaters - etc.

28. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
60 Hertz
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Clamp-on ammeter.

29. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Kilovolt ampere (KVA).
5:1
Inductance.
2000 watts

30. What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
75 turns.
60 cycles per second (60 Hertz).
60 Hertz

31. 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?
100 turns.
Because less current flowing at high voltage causes less line loss per kilowatt.
Nearly constant.
600 volts.

32. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Squirrel-cage rotor.
Current changing constantly in magnitude and periodically in direction.
Capacitance.

33. A solenoid coil is...
2000 watts
An electromagnet.
800 volts.
12 to 15 times a minute.

34. The standard frequency of alternating current used at a mine is...
Reverse any two-phase leads.
No.6 AWG.
277 volts.
60 Hertz

35. What should the duty rating of a grounding resistor be?
5:1
Provides single-phase power to smaller loads such as lights - heaters - etc.
100 turns.
Continuous.

36. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
An electromagnet.
Tied together
15 feet off the ground.
They must be installed at least 7 feet above the ground.

37. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
The motor rotation is reversed.
Inductance.
Reverse any two-phase leads.

38. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Circuit Breaker.
Allow for metering voltage and Current.
At least two phases

39. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
H terminals.
Zero amps.
Continuous.
60 cycles per second (60 Hertz).

40. What steps up or steps down AC voltage?
Transformer
480 volts.
Current changing constantly in magnitude and periodically in direction.
75 turns.

41. Where should grounding resistors be located?
Disconnect the frame-grounding conductor.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Lower current and higher voltage
At the source transformer.

42. 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?
Reverse any two-phase leads.
Four times less than that of the secondary.
3 -979 Volts.
200 volts AC.

43. At what rate should mouth-to-mouth resuscitation be applied?
600 volts.
12 to 15 times a minute.
Current changing constantly in magnitude and periodically in direction.
Nearly constant.

44. The property of an electrical circuit that opposes any change in voltage is called...
Short-circuited after power has been removed.
A step-up transformer.
Capacitance.
1 amp.

45. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
277 volts.
Transformers.
At least two phases

46. Alternating current may be defined as...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Current that changes constantly in magnitude and periodically in direction.
15 feet off the ground.
At the source transformer.

47. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
2000 watts
Electro-magnetism for their operation.

48. The primary leads of a single-phase transformer should be connected to the...
Nearly constant.
Squirrel-cage rotor.
Transformer
H terminals.

49. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Zero amps.
1 amp.
Reverse its rotation.
Lower current and higher voltage

50. 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.
A grounding resistor.
Transformer
60 cycles per second (60 Hertz).