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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 burn causing a blister is classified as a...
15 feet off the ground.
Hyperventilation.
Potential transformer.
Second-degree burn.

2. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The sum of the two capacitors.
The motor rotation is reversed.
At the source transformer.
1 amp.

3. 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?
800 volts.
Derive a neutral for grounding purposes.
No.6 AWG.
5:1.

4. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Current changing constantly in magnitude and periodically in direction.
Tied together
Hyperventilation.

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.
Draw less current.
Grounded phase and ground fault devices were not operating.
200 volts AC.

6. Define alternating current...
Draw less current.
It provides good speed control.
Reverse any two-phase leads.
Current changing constantly in magnitude and periodically in direction.

7. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Draw less current.
Squirrel-cage rotor.
Transformer
Grounded phase and ground fault devices were not operating.

8. The standard frequency of power supplied by the power company is...
Shunted and taped
60 cycles per second (60 Hertz).
They should be made by the same manufacturer.
200 volts AC.

9. How do you change the direction of a 3-phase AC motor?
Squirrel-cage induction motor.
Reverse any two-phase leads.
Zero amps.
Second-degree burn.

10. All transformers step voltage up or down by...
Two speeds
No.6 AWG.
Inductance.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

11. 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?
600 volts.
Continuous.
Two speeds
No.6 AWG.

12. How should clothing be removed from a burn?
Nearly constant.
A step-up transformer.
Cut around clothing that has adhered to the burned area.
No.6 AWG.

13. What type motor is a wound-rotor induction motor?
A step-up transformer.
Electro-magnetism for their operation.
Circuit Breaker.
A.C.

14. High voltage is used to transmit power over long distances...
480 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
They should be made by the same manufacturer.
15 feet off the ground.

15. 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?
They should be made by the same manufacturer.
75 turns.
Derive a neutral for grounding purposes.
Inductance.

16. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
2000 watts
100 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

17. A wound-rotor induction motor has all the following EXCEPT...
Current that changes constantly in magnitude and periodically in direction.
The sum of the two capacitors.
100 volts.
Squirrel-cage rotor.

18. 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.
A.C.
Zero amps.
75 turns.

19. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
100 turns.
15 feet off the ground.
600 volts.
Disconnect the frame-grounding conductor.

20. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
An electromagnet.
1 amp.
Alternating current.
Nearly constant.

21. Not true about AC power?
12 to 15 times a minute.
A grounding resistor.
Isolation transformer.
It provides good speed control.

22. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
12 to 15 times a minute.
Short-circuited after power has been removed.
Cut around clothing that has adhered to the burned area.

23. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
100 turns.
Lower current and higher voltage.
7 -630 volts.
Current that changes constantly in magnitude and periodically in direction.

24. The primary leads of a single-phase transformer should be connected to the...
No.6 AWG.
150 turns.
Disconnect the frame-grounding conductor.
H terminals.

25. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
25 feet.
277 volts.
5:1.
Draw less current.

26. What type of 3-phase AC motor is used most often around a mine?
Check to make sure that the victim is not still in contact with the electricity.
Transformers.
A grounding resistor.
Squirrel-cage induction motor.

27. 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 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.
At least two phases

28. The secondary windings on a 10:1 step-down transformer will have a wire size...
Kilovolt ampere (KVA).
800 volts.
Current that changes constantly in magnitude and periodically in direction.
Larger than that found in the primary winding.

29. What steps up or steps down AC voltage?
Transformer
Reverse any two-phase leads.
Provides single-phase power to smaller loads such as lights - heaters - etc.
7 -630 volts.

30. 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...
Tied together
Alternating current.
Disconnect the frame-grounding conductor.
Draw less current.

31. 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.
Carotid pulse - which is located in the neck next to the Adam's apple.
No.6 AWG.
The current will read zero.

32. Which of the following does a squirrel cage induction motor have?
100 turns.
A.C.
Draw less current.
Stator windings.

33. A control power transformer...
A.C.
60 Hertz
Provides single-phase power to smaller loads such as lights - heaters - etc.
The current will read zero.

34. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
60 Hertz
At the source transformer.
3 -979 Volts.

35. The transformer used only to measure voltage is a...
No.6 AWG.
They must be installed at least 7 feet above the ground.
1 amp.
Potential transformer.

36. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
A step-up transformer.
Two speeds
The capacitors should be discharged.
Draw less current.

37. Compared to the secondary of a loaded - step-down transformer - the primary has...
At least two phases
They must be installed at least 7 feet above the ground.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Lower current and higher voltage

38. The combined capacitance of two capacitors in parallel is...
Because less current flowing at high voltage causes less line loss per kilowatt.
The sum of the two capacitors.
A.C.
12 to 15 times a minute.

39. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Four times less than that of the secondary.
100 turns.
60 cycles per second (60 Hertz).
The capacitors should be discharged.

40. Not a symptom of electrical shock?.
Lower current and higher voltage
Circuit Breaker.
Hyperventilation.
Kilovolt ampere (KVA).

41. If any two-phase wires are reversed on a three-phase motor - the motor will...
Kilovolt ampere (KVA).
Reverse its rotation.
Larger than that found in the primary winding.
7 -630 volts.

42. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Full-load - three-phase voltage.
Lower current and higher voltage
Reverse its rotation.

43. At what rate should mouth-to-mouth resuscitation be applied?
Transformer
480 volts.
12 to 15 times a minute.
Nearly constant.

44. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
277 volts.
Kilovolt ampere (KVA).
Carotid pulse - which is located in the neck next to the Adam's apple.

45. Not an acceptable method for the installations of surface transformers?
The motor rotation is reversed.
5:1.
Draw less current.
They must be installed at least 7 feet above the ground.

46. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Inductance.
800 volts.
15 feet off the ground.
At least two phases

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

48. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Allow for metering voltage and Current.
At least two phases
The capacitors should be discharged.
3 -979 Volts.

49. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
A grounding resistor.
They should be made by the same manufacturer.
No.6 AWG.
600 volts.

50. The standard frequency of alternating current used at a mine is...
Four times less than that of the secondary.
Draw less current.
Current changing constantly in magnitude and periodically in direction.
60 Hertz