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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. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Tied together
The current will read zero.
It provides good speed control.
Reverse any two-phase leads.

2. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
They should be made by the same manufacturer.
Stator windings.
60 cycles per second (60 Hertz).

3. Current in an AC circuit may be measured by...
12 to 15 times a minute.
Transformer
Clamp-on ammeter.
Stator windings.

4. A control power transformer...
No.6 AWG.
Second-degree burn.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Zero amps.

5. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
5:1.
600 volts.
Hyperventilation.

6. What is a capacitor?
Two speeds
A device used to store electrical energy.
The motor rotation is reversed.
150 turns.

7. 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?
3 -979 Volts.
75 turns.
Squirrel-cage induction motor.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

8. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
No.6 AWG.
Two speeds
Kilovolt ampere (KVA).
Provides single-phase power to smaller loads such as lights - heaters - etc.

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

10. What type motor is a wound-rotor induction motor?
2000 watts
Inductance.
A.C.
60 Hertz

11. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
A step-up transformer.
A grounding resistor.
1 amp.
60 cycles per second (60 Hertz).

12. Where should grounding resistors be located?
Reverse any two-phase leads.
At the source transformer.
Two speeds
A step-up transformer.

13. A transformer has a primary voltage of 2 -400 volts and a secondary reading of 120 volts. If there are 1 -500 turns on the primary - how many turns are on the secondary?
Inductance.
At least two phases
75 turns.
Capacitance.

14. The combined capacitance of two capacitors in parallel is...
Disconnect the frame-grounding conductor.
The sum of the two capacitors.
The motor rotation is reversed.
60 cycles per second (60 Hertz).

15. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Draw less current.
Second-degree burn.
Inductance.
Grounded phase and ground fault devices were not operating.

16. How should clothing be removed from a burn?
Provides single-phase power to smaller loads such as lights - heaters - etc.
Cut around clothing that has adhered to the burned area.
They should be made by the same manufacturer.
Draw less current.

17. What steps up or steps down AC voltage?
The sum of the two capacitors.
Transformer
Squirrel-cage induction motor.
7 -630 volts.

18. Compared to the secondary of a loaded - step-down transformer - the primary has...
100 turns.
Lower current and higher voltage.
Tied together
12 to 15 times a minute.

19. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
At least two phases
A grounding resistor.
Potential transformer.
Check to make sure that the victim is not still in contact with the electricity.

20. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
They must be installed at least 7 feet above the ground.
The chest should rise or inflate.
3 -979 Volts.
Allow for metering voltage and Current.

21. 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.
60 Hertz
No.6 AWG.
800 volts.

22. Operating coils - motors - transformers - relays and solenoids depend upon...
Continuous.
Reverse its rotation.
100 turns.
Electro-magnetism for their operation.

23. 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.
Squirrel-cage induction motor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
12 to 15 times a minute.

24. A burn causing a blister is classified as a...
Second-degree burn.
Squirrel-cage induction motor.
Potential transformer.
Electro-magnetism for their operation.

25. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Grounded phase and ground fault devices were not operating.
277 volts.
Second-degree burn.
Stator windings.

26. 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.
5:1.
5:1
Stator windings.
An electrical shock hazard may exist.

27. The speed of an alternating current - squirrel-cage induction motor is...
A device used to store electrical energy.
At least two phases
Second-degree burn.
Nearly constant.

28. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Electro-magnetism for their operation.
A step-up transformer.
Zero amps.
600 volts.

29. The property of an electrical circuit that opposes any change in voltage is called...
They must be installed at least 7 feet above the ground.
Capacitance.
277 volts.
Tied together

30. 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?
Derive a neutral for grounding purposes.
A device used to store electrical energy.
An electromagnet.
800 volts.

31. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
At the source transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
75 turns.
Provides single-phase power to smaller loads such as lights - heaters - etc.

32. The size of a transformer is measured in...
480 volts.
Kilovolt ampere (KVA).
An electrical shock hazard may exist.
5:1.

33. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse any two-phase leads.
X.
600 volts.
Reverse its rotation.

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

35. Alternating current may be defined as...
At the source transformer.
Zero amps.
Kilovolt ampere (KVA).
Current that changes constantly in magnitude and periodically in direction.

36. The primary leads of a single-phase transformer should be connected to the...
H terminals.
200 volts AC.
Transformers.
60 Hertz

37. 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...
75 turns.
Draw less current.
An electrical shock hazard may exist.
Potential transformer.

38. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Nearly constant.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Cut around clothing that has adhered to the burned area.

39. Which of the following does a squirrel cage induction motor have?
200 volts AC.
75 turns.
It provides good speed control.
Stator windings.

40. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
100 turns.
Two speeds
They should be made by the same manufacturer.
7 -630 volts.

41. What is the danger when working around capacitors?
60 Hertz
100 volts.
An electrical shock hazard may exist.
Clamp-on ammeter.

42. 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...
Tied together
Clamp-on ammeter.
Draw less current.
Lower current and higher voltage.

43. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Transformers.
15 feet off the ground.
Draw less current.
At least two phases

44. What is the first step to be followed in aiding a victim of electrical shock?
It provides good speed control.
Check to make sure that the victim is not still in contact with the electricity.
60 Hertz
Larger than that found in the primary winding.

45. The standard frequency of alternating current used at a mine is...
800 volts.
60 Hertz
An electrical shock hazard may exist.
An electromagnet.

46. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
75 turns.
Alternating current.
5:1

47. AC voltage is raised or lowered by means of...
Grounded phase and ground fault devices were not operating.
The sum of the two capacitors.
Transformers.
Draw less current.

48. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Nearly constant.
Hyperventilation.
Stator windings.

49. 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.
Lower current and higher voltage
Two speeds
Inductance.

50. The standard frequency of power supplied by the power company is...
The sum of the two capacitors.
60 cycles per second (60 Hertz).
The current will read zero.
Kilovolt ampere (KVA).