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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. A wound-rotor induction motor has all the following EXCEPT...
150 turns.
25 feet.
3 -979 Volts.
Squirrel-cage rotor.

2. A burn causing a blister is classified as a...
Inductance.
60 Hertz
No.6 AWG.
Second-degree burn.

3. Where should grounding resistors be located?
At the source transformer.
A grounding resistor.
480 volts.
15 feet off the ground.

4. 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?
3 -979 Volts.
At the source transformer.
Current that changes constantly in magnitude and periodically in direction.
Inductance.

5. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
277 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Short-circuited after power has been removed.

6. Compared to the secondary of a loaded - step-down transformer - the primary has...
Clamp-on ammeter.
The sum of the two capacitors.
Larger than that found in the primary winding.
Lower current and higher voltage.

7. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
They must be installed at least 7 feet above the ground.
Inductance.
5:1

8. If any two-phase wires are reversed on a three-phase motor - the motor will...
Current changing constantly in magnitude and periodically in direction.
Reverse its rotation.
12 to 15 times a minute.
1 amp.

9. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Disconnect the frame-grounding conductor.
Transformer
Alternating current.

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

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11. 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?
75 turns.
Check to make sure that the victim is not still in contact with the electricity.
Squirrel-cage induction motor.
100 turns.

12. When not connected to a load - the secondary leads of a current transformer should be...
Provides single-phase power to smaller loads such as lights - heaters - etc.
600 volts.
Shunted and taped
Cut around clothing that has adhered to the burned area.

13. The size of a transformer is measured in...
The sum of the two capacitors.
Kilovolt ampere (KVA).
Larger than that found in the primary winding.
Four times less than that of the secondary.

14. Define alternating current...
A step-up transformer.
Alternating current.
No.6 AWG.
Current changing constantly in magnitude and periodically in direction.

15. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
The motor rotation is reversed.
A grounding resistor.
Short-circuited after power has been removed.
Kilovolt ampere (KVA).

16. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
Transformer
Because less current flowing at high voltage causes less line loss per kilowatt.
12 to 15 times a minute.

17. The standard frequency of power supplied by the power company is...
At least two phases
60 cycles per second (60 Hertz).
A grounding resistor.
100 volts.

18. Not true about AC power?
A step-up transformer.
It provides good speed control.
The sum of the two capacitors.
Four times less than that of the secondary.

19. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
They should be made by the same manufacturer.
480 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
Inductance.

20. Not an acceptable method for the installations of surface transformers?
150 turns.
An electrical shock hazard may exist.
They must be installed at least 7 feet above the ground.
Isolation transformer.

21. Not a symptom of electrical shock?.
Reverse its rotation.
Continuous.
Hyperventilation.
A grounding resistor.

22. How should clothing be removed from a burn?
Larger than that found in the primary winding.
Cut around clothing that has adhered to the burned area.
Circuit Breaker.
Disconnect the frame-grounding conductor.

23. All transformers step voltage up or down by...
Lower current and higher voltage
Inductance.
2000 watts
15 feet off the ground.

24. 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...
277 volts.
150 turns.
Draw less current.
The sum of the two capacitors.

25. What type of 3-phase AC motor is used most often around a mine?
1 amp.
60 Hertz
Four times less than that of the secondary.
Squirrel-cage induction motor.

26. The purpose of a zig-zag transformer is to...
Capacitance.
Derive a neutral for grounding purposes.
5:1
They must be installed at least 7 feet above the ground.

27. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
They must be installed at least 7 feet above the ground.
Four times less than that of the secondary.
Circuit Breaker.
A.C.

28. The property of an electrical circuit that opposes any change in voltage is called...
The sum of the two capacitors.
No.6 AWG.
Capacitance.
200 volts AC.

29. At what rate should mouth-to-mouth resuscitation be applied?
60 cycles per second (60 Hertz).
277 volts.
Check to make sure that the victim is not still in contact with the electricity.
12 to 15 times a minute.

30. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Lower current and higher voltage
The current will read zero.
Disconnect the frame-grounding conductor.
Squirrel-cage rotor.

31. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Electro-magnetism for their operation.
Four times less than that of the secondary.
At the source transformer.
A step-up transformer.

32. 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?
Current that changes constantly in magnitude and periodically in direction.
600 volts.
An electrical shock hazard may exist.
Potential transformer.

33. The transformer used only to measure voltage is a...
Potential transformer.
At least two phases
Provides single-phase power to smaller loads such as lights - heaters - etc.
Draw less current.

34. 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...
Derive a neutral for grounding purposes.
277 volts.
Zero amps.
Draw less current.

35. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Two speeds
Carotid pulse - which is located in the neck next to the Adam's apple.
Disconnect the frame-grounding conductor.
12 to 15 times a minute.

36. 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.
Stator windings.
5:1
Potential transformer.
A device used to store electrical energy.

37. The property of an electric circuit that opposes any change in current is called...
Second-degree burn.
Inductance.
5:1
Circuit Breaker.

38. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Transformers.
A.C.
Zero amps.
A device used to store electrical energy.

39. Current that changes periodically in direction is...
Alternating current.
Reverse any two-phase leads.
Derive a neutral for grounding purposes.
Transformers.

40. Alternating current may be defined as...
Continuous.
Kilovolt ampere (KVA).
25 feet.
Current that changes constantly in magnitude and periodically in direction.

41. AC voltage is raised or lowered by means of...
Transformers.
Cut around clothing that has adhered to the burned area.
200 volts AC.
A step-up transformer.

42. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
A grounding resistor.
5:1.
At least two phases

43. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
They must be installed at least 7 feet above the ground.
15 feet off the ground.
Tied together
25 feet.

44. 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.
3 -979 Volts.
Circuit Breaker.

45. What is a capacitor?
Check to make sure that the victim is not still in contact with the electricity.
Shunted and taped
A device used to store electrical energy.
Four times less than that of the secondary.

46. The secondary windings on a 10:1 step-down transformer will have a wire size...
Two speeds
The sum of the two capacitors.
Larger than that found in the primary winding.
Transformer

47. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
An electromagnet.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Draw less current.

48. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Squirrel-cage induction motor.
At least two phases
Carotid pulse - which is located in the neck next to the Adam's apple.
Alternating current.

49. How do you change the direction of a 3-phase AC motor?
Check to make sure that the victim is not still in contact with the electricity.
Because less current flowing at high voltage causes less line loss per kilowatt.
800 volts.
Reverse any two-phase leads.

50. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Draw less current.
7 -630 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
100 turns.