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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. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
Stator windings.
Clamp-on ammeter.
3 -979 Volts.

2. A control power transformer...
Allow for metering voltage and Current.
Provides single-phase power to smaller loads such as lights - heaters - etc.
A grounding resistor.
Inductance.

3. 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?
100 volts.
75 turns.
150 turns.
Grounded phase and ground fault devices were not operating.

4. A burn causing a blister is classified as a...
5:1.
Second-degree burn.
Inductance.
Provides single-phase power to smaller loads such as lights - heaters - etc.

5. What is the danger when working around capacitors?
The sum of the two capacitors.
60 Hertz
The chest should rise or inflate.
An electrical shock hazard may exist.

6. 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?
Electro-magnetism for their operation.
Cut around clothing that has adhered to the burned area.
600 volts.
At least two phases

7. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Grounded phase and ground fault devices were not operating.
15 feet off the ground.
A grounding resistor.

8. 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...
A device used to store electrical energy.
Draw less current.
15 feet off the ground.
Squirrel-cage rotor.

9. When not connected to a load - the secondary leads of a current transformer should be...
Reverse its rotation.
Shunted and taped
H terminals.
Transformers.

10. 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?
Capacitance.
Full-load - three-phase voltage.
150 turns.
A.C.

11. Current transformers - or CT's - are used to...
An electromagnet.
Kilovolt ampere (KVA).
They should be made by the same manufacturer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

12. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Full-load - three-phase voltage.
277 volts.
100 turns.
Squirrel-cage induction motor.

13. Compared to the secondary of a loaded - step-down transformer - the primary has...
100 turns.
15 feet off the ground.
5:1.
Lower current and higher voltage.

14. How should clothing be removed from a burn?
Current changing constantly in magnitude and periodically in direction.
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.
Electro-magnetism for their operation.

15. What type motor is a wound-rotor induction motor?
H terminals.
Full-load - three-phase voltage.
Clamp-on ammeter.
A.C.

16. 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...
Current that changes constantly in magnitude and periodically in direction.
Capacitance.
Tied together
100 volts.

17. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Two speeds
Lower current and higher voltage
Potential transformer.

18. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Draw less current.
It provides good speed control.
The chest should rise or inflate.

19. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Draw less current.
60 Hertz
5:1.

20. What is a capacitor?
The sum of the two capacitors.
A device used to store electrical energy.
Nearly constant.
800 volts.

21. AC voltage is raised or lowered by means of...
200 volts AC.
Transformers.
Check to make sure that the victim is not still in contact with the electricity.
The capacitors should be discharged.

22. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
Isolation transformer.
Nearly constant.
75 turns.

23. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Draw less current.
60 cycles per second (60 Hertz).
800 volts.
1 amp.

24. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Derive a neutral for grounding purposes.
Because less current flowing at high voltage causes less line loss per kilowatt.
H terminals.

25. 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?
Transformer
Potential transformer.
200 volts AC.
They should be made by the same manufacturer.

26. 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?
They must be installed at least 7 feet above the ground.
Inductance.
800 volts.
60 cycles per second (60 Hertz).

27. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Squirrel-cage induction motor.
Carotid pulse - which is located in the neck next to the Adam's apple.
The capacitors should be discharged.
3 -979 Volts.

28. High voltage is used to transmit power over long distances...
1 amp.
Because less current flowing at high voltage causes less line loss per kilowatt.
A.C.
60 Hertz

29. The primary function of a power transformer is to provide...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Full-load - three-phase voltage.
The current will read zero.
Reverse its rotation.

30. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
The motor rotation is reversed.
3 -979 Volts.
An electrical shock hazard may exist.
2000 watts

31. The secondary windings on a 10:1 step-down transformer will have a wire size...
480 volts.
Larger than that found in the primary winding.
At the source transformer.
3 -979 Volts.

32. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Draw less current.
15 feet off the ground.
Current that changes constantly in magnitude and periodically in direction.
No.6 AWG.

33. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Allow for metering voltage and Current.
Reverse any two-phase leads.
Squirrel-cage induction motor.
The current will read zero.

34. The transformer used only to measure voltage is a...
Draw less current.
Potential transformer.
Lower current and higher voltage
Kilovolt ampere (KVA).

35. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
15 feet off the ground.
At least two phases
480 volts.
Capacitance.

36. 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...
800 volts.
277 volts.
100 volts.
The sum of the two capacitors.

37. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Larger than that found in the primary winding.
Draw less current.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Grounded phase and ground fault devices were not operating.

38. Where should grounding resistors be located?
Transformer
100 turns.
At the source transformer.
150 turns.

39. A solenoid coil is...
Allow for metering voltage and Current.
Grounded phase and ground fault devices were not operating.
An electromagnet.
Four times less than that of the secondary.

40. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
A device used to store electrical energy.
12 to 15 times a minute.
5:1.
No.6 AWG.

41. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
75 turns.
Lower current and higher voltage.
100 turns.

42. A transformer with a 1:1 ratio is usually a (an)...
200 volts AC.
At least two phases
Isolation transformer.
Reverse its rotation.

43. The property of an electric circuit that opposes any change in current is called...
7 -630 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
Inductance.
The sum of the two capacitors.

44. Not a symptom of electrical shock?.
Hyperventilation.
Squirrel-cage induction motor.
Reverse its rotation.
Shunted and taped

45. 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.
5:1.
Full-load - three-phase voltage.
At the source transformer.
Alternating current.

46. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Inductance.
Clamp-on ammeter.
Disconnect the frame-grounding conductor.
Grounded phase and ground fault devices were not operating.

47. What should the duty rating of a grounding resistor be?
Continuous.
Squirrel-cage induction motor.
The sum of the two capacitors.
Short-circuited after power has been removed.

48. A wound-rotor induction motor has all the following EXCEPT...
Draw less current.
Kilovolt ampere (KVA).
Squirrel-cage rotor.
Because less current flowing at high voltage causes less line loss per kilowatt.

49. 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?
Lower current and higher voltage.
75 turns.
Lower current and higher voltage
Allow for metering voltage and Current.

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