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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. AC voltage is raised or lowered by means of...
Transformers.
Allow for metering voltage and Current.
Because less current flowing at high voltage causes less line loss per kilowatt.
150 turns.

2. The combined capacitance of two capacitors in parallel is...
Nearly constant.
The chest should rise or inflate.
Current changing constantly in magnitude and periodically in direction.
The sum of the two capacitors.

3. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Disconnect the frame-grounding conductor.
At least two phases
800 volts.
Lower current and higher voltage

4. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
X.
Capacitance.
2000 watts

5. The speed of an alternating current - squirrel-cage induction motor is...
Disconnect the frame-grounding conductor.
Nearly constant.
1 amp.
Capacitance.

6. What type of 3-phase AC motor is used most often around a mine?
60 Hertz
Because less current flowing at high voltage causes less line loss per kilowatt.
7 -630 volts.
Squirrel-cage induction motor.

7. The transformer used only to measure voltage is a...
Potential transformer.
Hyperventilation.
600 volts.
800 volts.

8. What type motor is a wound-rotor induction motor?
They should be made by the same manufacturer.
Capacitance.
The capacitors should be discharged.
A.C.

9. 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?
200 volts AC.
3 -979 Volts.
At the source transformer.
Cut around clothing that has adhered to the burned area.

10. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Electro-magnetism for their operation.
Current that changes constantly in magnitude and periodically in direction.
200 volts AC.
No.6 AWG.

11. How do you change the direction of a 3-phase AC motor?
The capacitors should be discharged.
Reverse any two-phase leads.
5:1
A device used to store electrical energy.

12. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Disconnect the frame-grounding conductor.
25 feet.
Short-circuited after power has been removed.
15 feet off the ground.

13. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
Continuous.
Check to make sure that the victim is not still in contact with the electricity.
Hyperventilation.

14. Operating coils - motors - transformers - relays and solenoids depend upon...
Derive a neutral for grounding purposes.
Electro-magnetism for their operation.
Carotid pulse - which is located in the neck next to the Adam's apple.
The motor rotation is reversed.

15. A wound-rotor induction motor has all the following EXCEPT...
Capacitance.
H terminals.
Squirrel-cage rotor.
An electrical shock hazard may exist.

16. The secondary windings on a 10:1 step-down transformer will have a wire size...
2000 watts
A step-up transformer.
They must be installed at least 7 feet above the ground.
Larger than that found in the primary winding.

17. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
An electromagnet.
Short-circuited after power has been removed.
Grounded phase and ground fault devices were not operating.
A device used to store electrical energy.

18. Current that changes periodically in direction is...
Because less current flowing at high voltage causes less line loss per kilowatt.
Alternating current.
15 feet off the ground.
75 turns.

19. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
75 turns.
600 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
A grounding resistor.

20. Compared to the secondary of a loaded - step-down transformer - the primary has...
Carotid pulse - which is located in the neck next to the Adam's apple.
Squirrel-cage rotor.
Lower current and higher voltage
Two speeds

21. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
They should be made by the same manufacturer.
A device used to store electrical energy.
The capacitors should be discharged.
60 cycles per second (60 Hertz).

22. 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?
They must be installed at least 7 feet above the ground.
Transformer
200 volts AC.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

23. The size of a transformer is measured in...
Kilovolt ampere (KVA).
They must be installed at least 7 feet above the ground.
Electro-magnetism for their operation.
Larger than that found in the primary winding.

24. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Reverse its rotation.
At least two phases
X.
Squirrel-cage rotor.

25. At what rate should mouth-to-mouth resuscitation be applied?
150 turns.
12 to 15 times a minute.
Derive a neutral for grounding purposes.
Transformers.

26. 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?
75 turns.
Two speeds
Four times less than that of the secondary.
No.6 AWG.

27. Not an acceptable method for the installations of surface transformers?
200 volts AC.
Alternating current.
They must be installed at least 7 feet above the ground.
Two speeds

28. The primary leads of a single-phase transformer should be connected to the...
100 turns.
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.
H terminals.

29. Compared to the secondary of a loaded - step-down transformer - the primary has...
The capacitors should be discharged.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Lower current and higher voltage.
Provides single-phase power to smaller loads such as lights - heaters - etc.

30. Current in an AC circuit may be measured by...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
At least two phases
Clamp-on ammeter.
2000 watts

31. All transformers step voltage up or down by...
Inductance.
1 amp.
It provides good speed control.
Potential transformer.

32. Where should grounding resistors be located?
At the source transformer.
Transformers.
1 amp.
Alternating current.

33. Three-phase AC underground cables must be provided with overcurrent protection using a...
Lower current and higher voltage
X.
Hyperventilation.
Circuit Breaker.

34. 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?
Inductance.
Transformer
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
800 volts.

35. 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.
25 feet.
X.
480 volts.

36. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
Reverse its rotation.
Squirrel-cage rotor.
Tied together

37. 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?
7 -630 volts.
600 volts.
5:1
Clamp-on ammeter.

38. The main function of CT's and PT's on a main substation is to...
The motor rotation is reversed.
Allow for metering voltage and Current.
X.
They must be installed at least 7 feet above the ground.

39. What steps up or steps down AC voltage?
Transformer
Full-load - three-phase voltage.
Clamp-on ammeter.
Kilovolt ampere (KVA).

40. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
It provides good speed control.
5:1
A grounding resistor.

41. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
600 volts.
Isolation transformer.

42. The primary function of a power transformer is to provide...
1 amp.
Full-load - three-phase voltage.
Kilovolt ampere (KVA).
Squirrel-cage rotor.

43. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Zero amps.
Four times less than that of the secondary.
The motor rotation is reversed.
Carotid pulse - which is located in the neck next to the Adam's apple.

44. 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?
The capacitors should be discharged.
At least two phases
100 turns.
Kilovolt ampere (KVA).

45. Which of the following does a squirrel cage induction motor have?
Stator windings.
200 volts AC.
Four times less than that of the secondary.
Allow for metering voltage and Current.

46. The purpose of a zig-zag transformer is to...
12 to 15 times a minute.
Derive a neutral for grounding purposes.
75 turns.
Four times less than that of the secondary.

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...
Short-circuited after power has been removed.
Draw less current.
They must be installed at least 7 feet above the ground.
Continuous.

48. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
12 to 15 times a minute.
Disconnect the frame-grounding conductor.
Inductance.
277 volts.

49. What is a capacitor?
Lower current and higher voltage
A device used to store electrical energy.
Provides single-phase power to smaller loads such as lights - heaters - etc.
5:1

50. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
75 turns.
Shunted and taped
Capacitance.