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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. The standard frequency of alternating current used at a mine is...
Tied together
An electrical shock hazard may exist.
No.6 AWG.
60 Hertz

2. 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?
A device used to store electrical energy.
150 turns.
75 turns.
Second-degree burn.

3. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Second-degree burn.
The chest should rise or inflate.
No.6 AWG.
Clamp-on ammeter.

4. High voltage is used to transmit power over long distances...
15 feet off the ground.
Because less current flowing at high voltage causes less line loss per kilowatt.
The chest should rise or inflate.
Short-circuited after power has been removed.

5. All transformers step voltage up or down by...
A step-up transformer.
They must be installed at least 7 feet above the ground.
60 cycles per second (60 Hertz).
Inductance.

6. The combined capacitance of two capacitors in parallel is...
5:1
At the source transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
The sum of the two capacitors.

7. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
5:1.
The current will read zero.
Stator windings.
The capacitors should be discharged.

8. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Stator windings.
Isolation transformer.
An electromagnet.

9. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Shunted and taped
5:1.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

10. 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.
Hyperventilation.
5:1
Zero amps.
A.C.

11. Where should grounding resistors be located?
12 to 15 times a minute.
277 volts.
At the source transformer.
Lower current and higher voltage

12. What is a capacitor?
A device used to store electrical energy.
The capacitors should be discharged.
Zero amps.
Hyperventilation.

13. The speed of an alternating current - squirrel-cage induction motor is...
An electrical shock hazard may exist.
Nearly constant.
Tied together
600 volts.

14. A control power transformer...
12 to 15 times a minute.
3 -979 Volts.
The chest should rise or inflate.
Provides single-phase power to smaller loads such as lights - heaters - etc.

15. What steps up or steps down AC voltage?
Transformer
Capacitance.
12 to 15 times a minute.
The capacitors should be discharged.

16. Compared to the secondary of a loaded - step-down transformer - the primary has...
The capacitors should be discharged.
Lower current and higher voltage.
Lower current and higher voltage
2000 watts

17. 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?
Stator windings.
150 turns.
Lower current and higher voltage
75 turns.

18. Not an acceptable method for the installations of surface transformers?
The motor rotation is reversed.
Shunted and taped
Short-circuited after power has been removed.
They must be installed at least 7 feet above the ground.

19. When not connected to a load - the secondary leads of a current transformer should be...
Continuous.
600 volts.
Shunted and taped
Stator windings.

20. Current in an AC circuit may be measured by...
60 cycles per second (60 Hertz).
Clamp-on ammeter.
60 Hertz
75 turns.

21. What should the duty rating of a grounding resistor be?
75 turns.
Grounded phase and ground fault devices were not operating.
Continuous.
277 volts.

22. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Cut around clothing that has adhered to the burned area.
X.
Zero amps.
At least two phases

23. 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.
They should be made by the same manufacturer.
Cut around clothing that has adhered to the burned area.
Disconnect the frame-grounding conductor.

24. Not a symptom of electrical shock?.
H terminals.
Hyperventilation.
800 volts.
Lower current and higher voltage.

25. The purpose of a zig-zag transformer is to...
Circuit Breaker.
Derive a neutral for grounding purposes.
Squirrel-cage rotor.
Current that changes constantly in magnitude and periodically in direction.

26. AC voltage is raised or lowered by means of...
Alternating current.
Transformers.
Potential transformer.
A device used to store electrical energy.

27. What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
5:1.
1 amp.
Allow for metering voltage and Current.

28. 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?
60 Hertz
7 -630 volts.
150 turns.
100 turns.

29. Compared to the secondary of a loaded - step-down transformer - the primary has...
7 -630 volts.
Larger than that found in the primary winding.
Lower current and higher voltage
Allow for metering voltage and Current.

30. 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.
Potential transformer.
Two speeds
Grounded phase and ground fault devices were not operating.

31. What type motor is a wound-rotor induction motor?
Kilovolt ampere (KVA).
A.C.
5:1
Lower current and higher voltage

32. 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?
75 turns.
An electrical shock hazard may exist.
Full-load - three-phase voltage.
Lower current and higher voltage.

33. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
A.C.
200 volts AC.
The motor rotation is reversed.

34. The primary function of a power transformer is to provide...
150 turns.
Continuous.
Full-load - three-phase voltage.
Alternating current.

35. Current that changes periodically in direction is...
Alternating current.
The capacitors should be discharged.
600 volts.
Continuous.

36. Current transformers - or CT's - are used to...
Because less current flowing at high voltage causes less line loss per kilowatt.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Circuit Breaker.
Current that changes constantly in magnitude and periodically in direction.

37. A wound-rotor induction motor has all the following EXCEPT...
Because less current flowing at high voltage causes less line loss per kilowatt.
Capacitance.
Squirrel-cage rotor.
Cut around clothing that has adhered to the burned area.

38. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Grounded phase and ground fault devices were not operating.
Zero amps.
100 volts.
15 feet off the ground.

39. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
150 turns.
800 volts.
Check to make sure that the victim is not still in contact with the electricity.
2000 watts

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

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41. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Derive a neutral for grounding purposes.
They must be installed at least 7 feet above the ground.
800 volts.

42. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
A device used to store electrical energy.
600 volts.
Inductance.

43. Not true about AC power?
600 volts.
Four times less than that of the secondary.
A grounding resistor.
It provides good speed control.

44. 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.
Carotid pulse - which is located in the neck next to the Adam's apple.
Electro-magnetism for their operation.
Inductance.

45. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Second-degree burn.
Electro-magnetism for their operation.
480 volts.

46. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Full-load - three-phase voltage.
480 volts.
An electromagnet.

47. The transformer used only to measure voltage is a...
Transformers.
Potential transformer.
Allow for metering voltage and Current.
75 turns.

48. At what rate should mouth-to-mouth resuscitation be applied?
A.C.
12 to 15 times a minute.
Draw less current.
Circuit Breaker.

49. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Current that changes constantly in magnitude and periodically in direction.
Cut around clothing that has adhered to the burned area.
Potential transformer.
The motor rotation is reversed.

50. 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...
5:1
An electromagnet.
Tied together
75 turns.