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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. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
They must be installed at least 7 feet above the ground.
The current will read zero.
Disconnect the frame-grounding conductor.
Lower current and higher voltage

2. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
A.C.
A grounding resistor.
No.6 AWG.
Grounded phase and ground fault devices were not operating.

3. 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?
Allow for metering voltage and Current.
75 turns.
Zero amps.
100 volts.

4. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
3 -979 Volts.
5:1.
The sum of the two capacitors.
2000 watts

5. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
The current will read zero.
They should be made by the same manufacturer.
Zero amps.
Short-circuited after power has been removed.

6. When not connected to a load - the secondary leads of a current transformer should be...
Hyperventilation.
Tied together
Shunted and taped
600 volts.

7. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Draw less current.
100 turns.
The motor rotation is reversed.
Hyperventilation.

8. How do you change the direction of a 3-phase AC motor?
Alternating current.
Reverse any two-phase leads.
600 volts.
Inductance.

9. What type motor is a wound-rotor induction motor?
Draw less current.
At least two phases
A.C.
Disconnect the frame-grounding conductor.

10. 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...
Check to make sure that the victim is not still in contact with the electricity.
60 Hertz
Short-circuited after power has been removed.
Draw less current.

11. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
H terminals.
Inductance.
5:1.

12. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
The motor rotation is reversed.
12 to 15 times a minute.
3 -979 Volts.

13. 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...
They should be made by the same manufacturer.
60 Hertz
Disconnect the frame-grounding conductor.
Draw less current.

14. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
5:1
It provides good speed control.
Shunted and taped
They should be made by the same manufacturer.

15. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Squirrel-cage induction motor.
Transformers.
15 feet off the ground.

16. 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?
The chest should rise or inflate.
Inductance.
Hyperventilation.
150 turns.

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

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18. 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?
200 volts AC.
A step-up transformer.
800 volts.
Transformers.

19. Not a symptom of electrical shock?.
5:1.
75 turns.
Transformers.
Hyperventilation.

20. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
The chest should rise or inflate.
An electrical shock hazard may exist.
Derive a neutral for grounding purposes.

21. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
The current will read zero.
Check to make sure that the victim is not still in contact with the electricity.
Continuous.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

22. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Electro-magnetism for their operation.
7 -630 volts.
Shunted and taped
150 turns.

23. Current transformers - or CT's - are used to...
Transformer
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
X.
Provides single-phase power to smaller loads such as lights - heaters - etc.

24. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
H terminals.
Larger than that found in the primary winding.
No.6 AWG.

25. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Four times less than that of the secondary.
480 volts.
2000 watts

26. What is the danger when working around capacitors?
Two speeds
At the source transformer.
75 turns.
An electrical shock hazard may exist.

27. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Two speeds
Disconnect the frame-grounding conductor.
5:1
15 feet off the ground.

28. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
A step-up transformer.
The current will read zero.
A device used to store electrical energy.
They should be made by the same manufacturer.

29. 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.
They should be made by the same manufacturer.
Second-degree burn.
5:1.
Draw less current.

30. Compared to the secondary of a loaded - step-down transformer - the primary has...
12 to 15 times a minute.
5:1
Lower current and higher voltage.
75 turns.

31. The size of a transformer is measured in...
Kilovolt ampere (KVA).
H terminals.
Circuit Breaker.
Grounded phase and ground fault devices were not operating.

32. Current that changes periodically in direction is...
Squirrel-cage induction motor.
Alternating current.
Circuit Breaker.
It provides good speed control.

33. 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?
Carotid pulse - which is located in the neck next to the Adam's apple.
Transformers.
Reverse any two-phase leads.
200 volts AC.

34. Current in an AC circuit may be measured by...
Clamp-on ammeter.
150 turns.
H terminals.
Stator windings.

35. 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?
Kilovolt ampere (KVA).
75 turns.
3 -979 Volts.
Reverse its rotation.

36. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
The capacitors should be discharged.
Second-degree burn.
An electromagnet.
277 volts.

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

38. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Transformers.
A grounding resistor.
A device used to store electrical energy.
Cut around clothing that has adhered to the burned area.

39. What should the duty rating of a grounding resistor be?
Disconnect the frame-grounding conductor.
At least two phases
15 feet off the ground.
Continuous.

40. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Draw less current.
X.
100 turns.
75 turns.

41. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Hyperventilation.
7 -630 volts.
They must be installed at least 7 feet above the ground.
25 feet.

42. What is a capacitor?
Squirrel-cage rotor.
The current will read zero.
A device used to store electrical energy.
X.

43. A transformer with a 1:1 ratio is usually a (an)...
Kilovolt ampere (KVA).
Isolation transformer.
480 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

44. Which of the following does a squirrel cage induction motor have?
The sum of the two capacitors.
Potential transformer.
Stator windings.
Electro-magnetism for their operation.

45. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
75 turns.
Kilovolt ampere (KVA).
They should be made by the same manufacturer.

46. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Squirrel-cage induction motor.
Cut around clothing that has adhered to the burned area.
Potential transformer.

47. The secondary windings on a 10:1 step-down transformer will have a wire size...
Derive a neutral for grounding purposes.
Larger than that found in the primary winding.
5:1
Stator windings.

48. 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...
No.6 AWG.
25 feet.
Full-load - three-phase voltage.
Tied together

49. The transformer used only to measure voltage is a...
Stator windings.
Potential transformer.
480 volts.
7 -630 volts.

50. Not true about AC power?
It provides good speed control.
Reverse any two-phase leads.
Clamp-on ammeter.
Derive a neutral for grounding purposes.