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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. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
15 feet off the ground.
Squirrel-cage induction motor.
The chest should rise or inflate.

2. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Two speeds
75 turns.
Derive a neutral for grounding purposes.

3. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
Current changing constantly in magnitude and periodically in direction.
Grounded phase and ground fault devices were not operating.
Zero amps.

4. Operating coils - motors - transformers - relays and solenoids depend upon...
7 -630 volts.
Electro-magnetism for their operation.
A grounding resistor.
A.C.

5. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Grounded phase and ground fault devices were not operating.
Zero amps.
Check to make sure that the victim is not still in contact with the electricity.
A step-up transformer.

6. What type motor is a wound-rotor induction motor?
At least two phases
Carotid pulse - which is located in the neck next to the Adam's apple.
100 volts.
A.C.

7. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Draw less current.
Shunted and taped
Isolation transformer.

8. 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.
Reverse any two-phase leads.
Hyperventilation.
1 amp.

9. The secondary windings on a 10:1 step-down transformer will have a wire size...
Isolation transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
They should be made by the same manufacturer.
Larger than that found in the primary winding.

10. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
5:1.
Hyperventilation.
800 volts.
X.

11. What is the first step to be followed in aiding a victim of electrical shock?
It provides good speed control.
Current that changes constantly in magnitude and periodically in direction.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Check to make sure that the victim is not still in contact with the electricity.

12. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
75 turns.
Check to make sure that the victim is not still in contact with the electricity.
A.C.

13. 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...
200 volts AC.
Tied together
Shunted and taped
Full-load - three-phase voltage.

14. The standard frequency of alternating current used at a mine is...
Squirrel-cage induction motor.
60 Hertz
Capacitance.
Lower current and higher voltage.

15. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Four times less than that of the secondary.
Because less current flowing at high voltage causes less line loss per kilowatt.
Lower current and higher voltage.
Reverse its rotation.

16. A burn causing a blister is classified as a...
It provides good speed control.
60 cycles per second (60 Hertz).
Cut around clothing that has adhered to the burned area.
Second-degree burn.

17. 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.
Allow for metering voltage and Current.
Shunted and taped
It provides good speed control.

18. The property of an electrical circuit that opposes any change in voltage is called...
Larger than that found in the primary winding.
Because less current flowing at high voltage causes less line loss per kilowatt.
Capacitance.
800 volts.

19. 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?
200 volts AC.
75 turns.
The capacitors should be discharged.
Two speeds

20. 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?
Inductance.
Squirrel-cage induction motor.
Inductance.
600 volts.

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

22. Define alternating current...
Derive a neutral for grounding purposes.
Current changing constantly in magnitude and periodically in direction.
2000 watts
The motor rotation is reversed.

23. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
1 amp.
15 feet off the ground.
Lower current and higher voltage.
12 to 15 times a minute.

24. A control power transformer...
It provides good speed control.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Allow for metering voltage and Current.
1 amp.

25. Current transformers - or CT's - are used to...
Current that changes constantly in magnitude and periodically in direction.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Current changing constantly in magnitude and periodically in direction.
Two speeds

26. 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.
5:1.
Draw less current.
12 to 15 times a minute.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

27. What is a capacitor?
A device used to store electrical energy.
Lower current and higher voltage.
Larger than that found in the primary winding.
480 volts.

28. The standard frequency of power supplied by the power company is...
Electro-magnetism for their operation.
Alternating current.
60 cycles per second (60 Hertz).
Potential transformer.

29. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
800 volts.
Current that changes constantly in magnitude and periodically in direction.
Potential transformer.
Grounded phase and ground fault devices were not operating.

30. What steps up or steps down AC voltage?
H terminals.
Tied together
Hyperventilation.
Transformer

31. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
1 amp.
Grounded phase and ground fault devices were not operating.
5:1

32. When not connected to a load - the secondary leads of a current transformer should be...
Stator windings.
Transformers.
Shunted and taped
Inductance.

33. 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.
60 Hertz
The current will read zero.
800 volts.
5:1

34. The property of an electric circuit that opposes any change in current is called...
200 volts AC.
Allow for metering voltage and Current.
Cut around clothing that has adhered to the burned area.
Inductance.

35. Which of the following does a squirrel cage induction motor have?
7 -630 volts.
Stator windings.
1 amp.
Inductance.

36. AC voltage is raised or lowered by means of...
Transformers.
A step-up transformer.
200 volts AC.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

37. Current in an AC circuit may be measured by...
Clamp-on ammeter.
No.6 AWG.
150 turns.
An electrical shock hazard may exist.

38. 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?
2000 watts
5:1.
200 volts AC.
Squirrel-cage induction motor.

39. 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?
25 feet.
Potential transformer.
Draw less current.
100 turns.

40. The size of a transformer is measured in...
Kilovolt ampere (KVA).
75 turns.
Circuit Breaker.
Shunted and taped

41. 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...
Larger than that found in the primary winding.
Draw less current.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Clamp-on ammeter.

42. All transformers step voltage up or down by...
Two speeds
The chest should rise or inflate.
Potential transformer.
Inductance.

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

44. The primary leads of a single-phase transformer should be connected to the...
A step-up transformer.
H terminals.
150 turns.
277 volts.

45. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Derive a neutral for grounding purposes.
Full-load - three-phase voltage.
They should be made by the same manufacturer.
Current that changes constantly in magnitude and periodically in direction.

46. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
Tied together
Shunted and taped
Current changing constantly in magnitude and periodically in direction.

47. Not true about AC power?
Continuous.
It provides good speed control.
Because less current flowing at high voltage causes less line loss per kilowatt.
Transformer

48. 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
Nearly constant.
Circuit Breaker.
Provides single-phase power to smaller loads such as lights - heaters - etc.

49. What is the danger when working around capacitors?
Capacitance.
25 feet.
Two speeds
An electrical shock hazard may exist.

50. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Isolation transformer.
Check to make sure that the victim is not still in contact with the electricity.
Larger than that found in the primary winding.
A grounding resistor.

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Test your basic knowledge |

AC Theory

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3d Computer Modeling

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Adobe Indesign Publishing

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Adobe Photoshop CS 5 Keyboard Shortcuts

Adobe Photoshop Graphic Design

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Adobe Premiere Keyboard Shortcuts

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After Effects Keyboard Shortcuts

Agile Development

Agile Scrum Methodology

Ajax

Android Programming

Animation

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