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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. Compared to the secondary of a loaded - step-down transformer - the primary has...
Stator windings.
The chest should rise or inflate.
Disconnect the frame-grounding conductor.
Lower current and higher voltage.

2. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
1 amp.
480 volts.
Reverse its rotation.
277 volts.

3. What is the first step to be followed in aiding a victim of electrical shock?
A device used to store electrical energy.
Zero amps.
60 cycles per second (60 Hertz).
Check to make sure that the victim is not still in contact with the electricity.

4. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
A device used to store electrical energy.
800 volts.
12 to 15 times a minute.

5. Current in an AC circuit may be measured by...
Allow for metering voltage and Current.
Clamp-on ammeter.
5:1
Inductance.

6. To protect against over-current in a three-phase circuit over-current protection must be provided for...
800 volts.
At least two phases
Check to make sure that the victim is not still in contact with the electricity.
100 turns.

7. What is a capacitor?
A device used to store electrical energy.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Disconnect the frame-grounding conductor.
An electromagnet.

8. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Draw less current.
No.6 AWG.
3 -979 Volts.
An electrical shock hazard may exist.

9. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Grounded phase and ground fault devices were not operating.
150 turns.
Shunted and taped
Hyperventilation.

10. High voltage is used to transmit power over long distances...
An electrical shock hazard may exist.
Second-degree burn.
277 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.

11. What steps up or steps down AC voltage?
480 volts.
Transformer
5:1
The chest should rise or inflate.

12. How should clothing be removed from a burn?
Nearly constant.
7 -630 volts.
A device used to store electrical energy.
Cut around clothing that has adhered to the burned area.

13. Not a symptom of electrical shock?.
Hyperventilation.
A grounding resistor.
The sum of the two capacitors.
7 -630 volts.

14. A wound-rotor induction motor has all the following EXCEPT...
At the source transformer.
12 to 15 times a minute.
Squirrel-cage rotor.
Draw less current.

15. 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?
60 Hertz
200 volts AC.
Full-load - three-phase voltage.
Reverse any two-phase leads.

16. 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.
An electrical shock hazard may exist.
800 volts.
5:1.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

17. How do you change the direction of a 3-phase AC motor?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Reverse any two-phase leads.
277 volts.
A grounding resistor.

18. The combined capacitance of two capacitors in parallel is...
600 volts.
A step-up transformer.
X.
The sum of the two capacitors.

19. What type of 3-phase AC motor is used most often around a mine?
The chest should rise or inflate.
5:1
Squirrel-cage induction motor.
Check to make sure that the victim is not still in contact with the electricity.

20. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Derive a neutral for grounding purposes.
Grounded phase and ground fault devices were not operating.
H terminals.
X.

21. The transformer used only to measure voltage is a...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Potential transformer.
Derive a neutral for grounding purposes.
Zero amps.

22. The primary function of a power transformer is to provide...
Second-degree burn.
A.C.
Isolation transformer.
Full-load - three-phase voltage.

23. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
2000 watts
Larger than that found in the primary winding.
Electro-magnetism for their operation.
The chest should rise or inflate.

24. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Reverse its rotation.
Clamp-on ammeter.
Carotid pulse - which is located in the neck next to the Adam's apple.
Short-circuited after power has been removed.

25. The property of an electrical circuit that opposes any change in voltage is called...
Short-circuited after power has been removed.
Capacitance.
Two speeds
Stator windings.

26. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Nearly constant.
H terminals.
Lower current and higher voltage.

27. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Derive a neutral for grounding purposes.
1 amp.
480 volts.
A step-up transformer.

28. 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?
12 to 15 times a minute.
Reverse its rotation.
Electro-magnetism for their operation.
800 volts.

29. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
Inductance.
Check to make sure that the victim is not still in contact with the electricity.
Short-circuited after power has been removed.

30. 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.
Transformer
Four times less than that of the secondary.
15 feet off the ground.

31. The standard frequency of alternating current used at a mine is...
No.6 AWG.
Current that changes constantly in magnitude and periodically in direction.
60 Hertz
The motor rotation is reversed.

32. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Shunted and taped
The capacitors should be discharged.
150 turns.
A device used to store electrical energy.

33. What is the danger when working around capacitors?
An electrical shock hazard may exist.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Alternating current.
Tied together

34. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Disconnect the frame-grounding conductor.
At the source transformer.
2000 watts
800 volts.

35. What should the duty rating of a grounding resistor be?
An electromagnet.
Continuous.
150 turns.
1 amp.

36. Current transformers - or CT's - are used to...
75 turns.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The motor rotation is reversed.
Provides single-phase power to smaller loads such as lights - heaters - etc.

37. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
5:1
At the source transformer.
Reverse its rotation.
7 -630 volts.

38. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Current that changes constantly in magnitude and periodically in direction.
7 -630 volts.
Electro-magnetism for their operation.
The current will read zero.

39. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
200 volts AC.
X.
7 -630 volts.
1 amp.

40. The purpose of a zig-zag transformer is to...
The sum of the two capacitors.
5:1.
Derive a neutral for grounding purposes.
Clamp-on ammeter.

41. 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?
277 volts.
3 -979 Volts.
480 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.

42. Where should grounding resistors be located?
At the source transformer.
Isolation transformer.
800 volts.
150 turns.

43. A solenoid coil is...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
An electromagnet.
Cut around clothing that has adhered to the burned area.
Potential transformer.

44. Define alternating current...
Stator windings.
3 -979 Volts.
Current changing constantly in magnitude and periodically in direction.
X.

45. The primary leads of a single-phase transformer should be connected to the...
Four times less than that of the secondary.
7 -630 volts.
H terminals.
The capacitors should be discharged.

46. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
25 feet.
They should be made by the same manufacturer.
Two speeds
Full-load - three-phase voltage.

47. 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?
150 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.
75 turns.
Stator windings.

48. Operating coils - motors - transformers - relays and solenoids depend upon...
The sum of the two capacitors.
Electro-magnetism for their operation.
A device used to store electrical energy.
Inductance.

49. If any two-phase wires are reversed on a three-phase motor - the motor will...
Short-circuited after power has been removed.
Reverse its rotation.
277 volts.
Squirrel-cage induction motor.

50. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Because less current flowing at high voltage causes less line loss per kilowatt.
60 Hertz
The chest should rise or inflate.