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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. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
15 feet off the ground.
800 volts.
The current will read zero.

2. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
200 volts AC.
600 volts.
Lower current and higher voltage

3. What is the first step to be followed in aiding a victim of electrical shock?
At least two phases
60 Hertz
Check to make sure that the victim is not still in contact with the electricity.
An electromagnet.

4. 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?
A device used to store electrical energy.
150 turns.
75 turns.
Full-load - three-phase voltage.

5. The property of an electric circuit that opposes any change in current is called...
Isolation transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
Inductance.
The chest should rise or inflate.

6. 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.
H terminals.
60 cycles per second (60 Hertz).
5:1

7. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
A step-up transformer.
Zero amps.
Squirrel-cage induction motor.
200 volts AC.

8. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
480 volts.
Cut around clothing that has adhered to the burned area.
Grounded phase and ground fault devices were not operating.
Allow for metering voltage and Current.

9. At what rate should mouth-to-mouth resuscitation be applied?
X.
Transformer
12 to 15 times a minute.
Full-load - three-phase voltage.

10. Not an acceptable method for the installations of surface transformers?
Allow for metering voltage and Current.
Reverse its rotation.
They must be installed at least 7 feet above the ground.
Lower current and higher voltage

11. Current in an AC circuit may be measured by...
Clamp-on ammeter.
480 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Two speeds

12. 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?
Current changing constantly in magnitude and periodically in direction.
200 volts AC.
2000 watts
They must be installed at least 7 feet above the ground.

13. 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...
Isolation transformer.
Draw less current.
Larger than that found in the primary winding.
Two speeds

14. What is the danger when working around capacitors?
Alternating current.
An electrical shock hazard may exist.
5:1.
Electro-magnetism for their operation.

15. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Transformers.
1 amp.
Current changing constantly in magnitude and periodically in direction.
Reverse its rotation.

16. Not a symptom of electrical shock?.
Hyperventilation.
They should be made by the same manufacturer.
Current that changes constantly in magnitude and periodically in direction.
60 cycles per second (60 Hertz).

17. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Continuous.
600 volts.
150 turns.
480 volts.

18. Current that changes periodically in direction is...
12 to 15 times a minute.
Potential transformer.
Inductance.
Alternating current.

19. What type of 3-phase AC motor is used most often around a mine?
100 volts.
Squirrel-cage induction motor.
480 volts.
Potential transformer.

20. Not true about AC power?
Derive a neutral for grounding purposes.
It provides good speed control.
Nearly constant.
The motor rotation is reversed.

21. AC voltage is raised or lowered by means of...
Capacitance.
3 -979 Volts.
Transformers.
480 volts.

22. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
5:1.
The current will read zero.
The sum of the two capacitors.

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

24. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Inductance.
A grounding resistor.
They should be made by the same manufacturer.
No.6 AWG.

25. What is a capacitor?
5:1
60 Hertz
A device used to store electrical energy.
Transformers.

26. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
Circuit Breaker.
A.C.
60 Hertz

27. How do you change the direction of a 3-phase AC motor?
Circuit Breaker.
Provides single-phase power to smaller loads such as lights - heaters - etc.
No.6 AWG.
Reverse any two-phase leads.

28. Define alternating current...
25 feet.
Draw less current.
Current changing constantly in magnitude and periodically in direction.
Tied together

29. The speed of an alternating current - squirrel-cage induction motor is...
A.C.
60 Hertz
Nearly constant.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

30. 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?
Provides single-phase power to smaller loads such as lights - heaters - etc.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Larger than that found in the primary winding.
600 volts.

31. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
The motor rotation is reversed.
Four times less than that of the secondary.
Inductance.
2000 watts

32. What steps up or steps down AC voltage?
Electro-magnetism for their operation.
Shunted and taped
100 turns.
Transformer

33. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Lower current and higher voltage
Circuit Breaker.
At least two phases
Larger than that found in the primary winding.

34. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Reverse its rotation.
Disconnect the frame-grounding conductor.
It provides good speed control.
150 turns.

35. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Alternating current.
Squirrel-cage induction motor.
Inductance.

36. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The sum of the two capacitors.
A step-up transformer.
The capacitors should be discharged.
5:1

37. What type motor is a wound-rotor induction motor?
A.C.
Check to make sure that the victim is not still in contact with the electricity.
Lower current and higher voltage
60 cycles per second (60 Hertz).

38. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
75 turns.
75 turns.
Inductance.
Short-circuited after power has been removed.

39. 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.
The motor rotation is reversed.
Full-load - three-phase voltage.
Because less current flowing at high voltage causes less line loss per kilowatt.

40. Compared to the secondary of a loaded - step-down transformer - the primary has...
Stator windings.
Kilovolt ampere (KVA).
Lower current and higher voltage
The capacitors should be discharged.

41. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
Kilovolt ampere (KVA).
Allow for metering voltage and Current.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

42. The secondary windings on a 10:1 step-down transformer will have a wire size...
X.
Disconnect the frame-grounding conductor.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Larger than that found in the primary winding.

43. Three-phase AC underground cables must be provided with overcurrent protection using a...
5:1.
5:1
Circuit Breaker.
Transformer

44. Where should grounding resistors be located?
At the source transformer.
100 turns.
75 turns.
Stator windings.

45. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Inductance.
15 feet off the ground.
Hyperventilation.
At the source transformer.

46. A solenoid coil is...
Capacitance.
The motor rotation is reversed.
An electromagnet.
Nearly constant.

47. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
480 volts.
277 volts.
800 volts.
Squirrel-cage induction motor.

48. The purpose of a zig-zag transformer is to...
5:1
Reverse its rotation.
Derive a neutral for grounding purposes.
Hyperventilation.

49. 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...
At the source transformer.
150 turns.
Draw less current.
3 -979 Volts.

50. The transformer used only to measure voltage is a...
100 volts.
Potential transformer.
They must be installed at least 7 feet above the ground.
Clamp-on ammeter.