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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 any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
The chest should rise or inflate.
Two speeds
Grounded phase and ground fault devices were not operating.

2. At what rate should mouth-to-mouth resuscitation be applied?
Two speeds
12 to 15 times a minute.
Alternating current.
Transformer

3. Define alternating current...
A device used to store electrical energy.
Alternating current.
Current changing constantly in magnitude and periodically in direction.
The current will read zero.

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?
Two speeds
800 volts.
Nearly constant.
200 volts AC.

5. When not connected to a load - the secondary leads of a current transformer should be...
Current that changes constantly in magnitude and periodically in direction.
75 turns.
Shunted and taped
Grounded phase and ground fault devices were not operating.

6. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Reverse any two-phase leads.
75 turns.
Grounded phase and ground fault devices were not operating.
Allow for metering voltage and Current.

7. 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...
An electromagnet.
Stator windings.
A step-up transformer.
100 volts.

8. 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?
Continuous.
Carotid pulse - which is located in the neck next to the Adam's apple.
100 turns.
H terminals.

9. The primary leads of a single-phase transformer should be connected to the...
Grounded phase and ground fault devices were not operating.
Draw less current.
At least two phases
H terminals.

10. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
7 -630 volts.
Disconnect the frame-grounding conductor.
Squirrel-cage induction motor.

11. A wound-rotor induction motor has all the following EXCEPT...
7 -630 volts.
Squirrel-cage rotor.
Carotid pulse - which is located in the neck next to the Adam's apple.
A.C.

12. What type of 3-phase AC motor is used most often around a mine?
1 amp.
Carotid pulse - which is located in the neck next to the Adam's apple.
Squirrel-cage induction motor.
5:1

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?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
75 turns.
A step-up transformer.
Zero amps.

14. Which of the following does a squirrel cage induction motor have?
A step-up transformer.
Grounded phase and ground fault devices were not operating.
At the source transformer.
Stator windings.

15. Compared to the secondary of a loaded - step-down transformer - the primary has...
Disconnect the frame-grounding conductor.
Continuous.
Lower current and higher voltage.
Two speeds

16. Not true about AC power?
Derive a neutral for grounding purposes.
It provides good speed control.
Allow for metering voltage and Current.
Draw less current.

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

18. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
277 volts.
It provides good speed control.
Because less current flowing at high voltage causes less line loss per kilowatt.
Capacitance.

19. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The current will read zero.
Larger than that found in the primary winding.
60 cycles per second (60 Hertz).

20. Compared to the secondary of a loaded - step-down transformer - the primary has...
60 Hertz
Alternating current.
Lower current and higher voltage
Hyperventilation.

21. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
800 volts.
Reverse its rotation.
An electromagnet.
Zero amps.

22. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Potential transformer.
X.
75 turns.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

23. 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?
150 turns.
100 volts.
Transformers.
Alternating current.

24. The standard frequency of alternating current used at a mine is...
800 volts.
Potential transformer.
No.6 AWG.
60 Hertz

25. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Two speeds
Nearly constant.
Four times less than that of the secondary.
15 feet off the ground.

26. All transformers step voltage up or down by...
Inductance.
Nearly constant.
Full-load - three-phase voltage.
Transformer

27. 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...
Draw less current.
Transformers.
The chest should rise or inflate.
The current will read zero.

28. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
An electromagnet.
75 turns.
1 amp.
At the source transformer.

29. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
3 -979 Volts.
75 turns.
Transformers.

30. 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?
Alternating current.
Draw less current.
75 turns.
Circuit Breaker.

31. What steps up or steps down AC voltage?
Because less current flowing at high voltage causes less line loss per kilowatt.
3 -979 Volts.
Transformer
Draw less current.

32. How should clothing be removed from a burn?
Draw less current.
Cut around clothing that has adhered to the burned area.
The capacitors should be discharged.
75 turns.

33. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
A.C.
They should be made by the same manufacturer.
Clamp-on ammeter.
Inductance.

34. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Potential transformer.
The motor rotation is reversed.
Lower current and higher voltage.
The capacitors should be discharged.

35. What is the danger when working around capacitors?
3 -979 Volts.
1 amp.
Squirrel-cage rotor.
An electrical shock hazard may exist.

36. 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.
Tied together
Disconnect the frame-grounding conductor.
200 volts AC.

37. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
60 cycles per second (60 Hertz).
Short-circuited after power has been removed.
Carotid pulse - which is located in the neck next to the Adam's apple.
Lower current and higher voltage

38. 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.
Provides single-phase power to smaller loads such as lights - heaters - etc.
The chest should rise or inflate.
5:1
It provides good speed control.

39. What is a capacitor?
75 turns.
12 to 15 times a minute.
A device used to store electrical energy.
1 amp.

40. Three-phase AC underground cables must be provided with overcurrent protection using a...
Short-circuited after power has been removed.
Circuit Breaker.
Kilovolt ampere (KVA).
At least two phases

41. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
1 amp.
Isolation transformer.
5:1.

42. A control power transformer...
100 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
60 Hertz
Tied together

43. The transformer used only to measure voltage is a...
3 -979 Volts.
Disconnect the frame-grounding conductor.
Potential transformer.
Alternating current.

44. Current in an AC circuit may be measured by...
Squirrel-cage induction motor.
Clamp-on ammeter.
Grounded phase and ground fault devices were not operating.
They must be installed at least 7 feet above the ground.

45. The property of an electric circuit that opposes any change in current is called...
Electro-magnetism for their operation.
Hyperventilation.
Inductance.
Because less current flowing at high voltage causes less line loss per kilowatt.

46. What should the duty rating of a grounding resistor be?
Alternating current.
75 turns.
Continuous.
Check to make sure that the victim is not still in contact with the electricity.

47. 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...
Isolation transformer.
Draw less current.
1 amp.
Current that changes constantly in magnitude and periodically in direction.

48. Not an acceptable method for the installations of surface transformers?
15 feet off the ground.
25 feet.
100 turns.
They must be installed at least 7 feet above the ground.

49. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Current that changes constantly in magnitude and periodically in direction.
The chest should rise or inflate.
12 to 15 times a minute.
Short-circuited after power has been removed.

50. The purpose of a zig-zag transformer is to...
150 turns.
Shunted and taped
Derive a neutral for grounding purposes.
60 cycles per second (60 Hertz).