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AC Theory

Instructions:

Answer 50 questions in 30 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. Where should grounding resistors be located?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Alternating current.
5:1.
At the source transformer.

2. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
The sum of the two capacitors.
Stator windings.
Transformer

3. The size of a transformer is measured in...
Lower current and higher voltage
Draw less current.
Kilovolt ampere (KVA).
Continuous.

4. 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.
25 feet.
5:1.
A device used to store electrical energy.
Because less current flowing at high voltage causes less line loss per kilowatt.

5. When not connected to a load - the secondary leads of a current transformer should be...
Capacitance.
Larger than that found in the primary winding.
Shunted and taped
7 -630 volts.

6. The standard frequency of alternating current used at a mine is...
Current that changes constantly in magnitude and periodically in direction.
Inductance.
60 Hertz
Because less current flowing at high voltage causes less line loss per kilowatt.

7. Which of the following does a squirrel cage induction motor have?
Stator windings.
Current that changes constantly in magnitude and periodically in direction.
100 turns.
Circuit Breaker.

8. How should clothing be removed from a burn?
Nearly constant.
X.
Cut around clothing that has adhered to the burned area.
The sum of the two capacitors.

9. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Disconnect the frame-grounding conductor.
Second-degree burn.
12 to 15 times a minute.

10. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
277 volts.
X.
Four times less than that of the secondary.
3 -979 Volts.

11. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
An electromagnet.
At the source transformer.
Capacitance.

12. A transformer with a 1:1 ratio is usually a (an)...
15 feet off the ground.
Isolation transformer.
3 -979 Volts.
Current changing constantly in magnitude and periodically in direction.

13. All transformers step voltage up or down by...
Carotid pulse - which is located in the neck next to the Adam's apple.
Isolation transformer.
Inductance.
75 turns.

14. The main function of CT's and PT's on a main substation is to...
480 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
25 feet.
Allow for metering voltage and Current.

15. The primary function of a power transformer is to provide...
2000 watts
Current changing constantly in magnitude and periodically in direction.
A step-up transformer.
Full-load - three-phase voltage.

16. Compared to the secondary of a loaded - step-down transformer - the primary has...
100 turns.
The sum of the two capacitors.
Current that changes constantly in magnitude and periodically in direction.
Lower current and higher voltage.

17. Operating coils - motors - transformers - relays and solenoids depend upon...
Two speeds
60 cycles per second (60 Hertz).
Disconnect the frame-grounding conductor.
Electro-magnetism for their operation.

18. The transformer used only to measure voltage is a...
Potential transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
At least two phases
277 volts.

19. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
7 -630 volts.
Reverse any two-phase leads.
Disconnect the frame-grounding conductor.

20. A wound-rotor induction motor has all the following EXCEPT...
600 volts.
3 -979 Volts.
Squirrel-cage rotor.
Second-degree burn.

21. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
Four times less than that of the secondary.
480 volts.
Transformers.

22. What is the first step to be followed in aiding a victim of electrical shock?
Grounded phase and ground fault devices were not operating.
Check to make sure that the victim is not still in contact with the electricity.
800 volts.
12 to 15 times a minute.

23. AC voltage is raised or lowered by means of...
25 feet.
Carotid pulse - which is located in the neck next to the Adam's apple.
Transformers.
No.6 AWG.

24. High voltage is used to transmit power over long distances...
Derive a neutral for grounding purposes.
Because less current flowing at high voltage causes less line loss per kilowatt.
A device used to store electrical energy.
Draw less current.

25. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
800 volts.
Kilovolt ampere (KVA).
The chest should rise or inflate.

26. 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.
5:1
Two speeds
They should be made by the same manufacturer.
800 volts.

27. What is a capacitor?
An electrical shock hazard may exist.
Lower current and higher voltage.
150 turns.
A device used to store electrical energy.

28. What steps up or steps down AC voltage?
Transformer
Draw less current.
Alternating current.
Nearly constant.

29. A burn causing a blister is classified as a...
Allow for metering voltage and Current.
Kilovolt ampere (KVA).
Second-degree burn.
Four times less than that of the secondary.

30. Not a symptom of electrical shock?.
Reverse its rotation.
Hyperventilation.
Two speeds
Larger than that found in the primary winding.

31. What is the danger when working around capacitors?
75 turns.
An electrical shock hazard may exist.
Circuit Breaker.
3 -979 Volts.

32. Not an acceptable method for the installations of surface transformers?
At least two phases
Potential transformer.
They must be installed at least 7 feet above the ground.
Two speeds

33. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Inductance.
The motor rotation is reversed.
600 volts.

34. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Short-circuited after power has been removed.
Draw less current.
Squirrel-cage induction motor.

35. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
No.6 AWG.
They should be made by the same manufacturer.
The chest should rise or inflate.
Zero amps.

36. 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?
Short-circuited after power has been removed.
200 volts AC.
Second-degree burn.
Stator windings.

37. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The current will read zero.
X.
Squirrel-cage rotor.
277 volts.

38. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
At the source transformer.
Grounded phase and ground fault devices were not operating.
480 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.

39. 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?
Reverse any two-phase leads.
600 volts.
800 volts.
An electromagnet.

40. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Reverse any two-phase leads.
150 turns.
60 Hertz
A grounding resistor.

41. 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...
Short-circuited after power has been removed.
Tied together
25 feet.
A step-up transformer.

42. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
No.6 AWG.
Squirrel-cage rotor.
Full-load - three-phase voltage.

43. 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...
Nearly constant.
No.6 AWG.
Draw less current.
The capacitors should be discharged.

44. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Potential transformer.
12 to 15 times a minute.
At least two phases
60 cycles per second (60 Hertz).

45. 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?
An electromagnet.
75 turns.
Because less current flowing at high voltage causes less line loss per kilowatt.
Disconnect the frame-grounding conductor.

46. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
800 volts.
Circuit Breaker.
2000 watts

47. Current that changes periodically in direction is...
Alternating current.
A device used to store electrical energy.
15 feet off the ground.
Hyperventilation.

48. What type motor is a wound-rotor induction motor?
A grounding resistor.
Electro-magnetism for their operation.
A.C.
The motor rotation is reversed.

49. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Shunted and taped
Four times less than that of the secondary.
60 Hertz
Check to make sure that the victim is not still in contact with the electricity.

50. 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?
800 volts.
They should be made by the same manufacturer.
60 cycles per second (60 Hertz).
3 -979 Volts.