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AC Theory

Instructions:

Answer 50 questions in 15 minutes.
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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 solenoid coil is...
60 cycles per second (60 Hertz).
The current will read zero.
An electromagnet.
100 turns.

2. Alternating current may be defined as...
Current changing constantly in magnitude and periodically in direction.
Reverse any two-phase leads.
Hyperventilation.
Current that changes constantly in magnitude and periodically in direction.

3. 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?
Larger than that found in the primary winding.
A.C.
Disconnect the frame-grounding conductor.
100 turns.

4. 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...
Cut around clothing that has adhered to the burned area.
Draw less current.
Stator windings.
200 volts AC.

5. 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?
Disconnect the frame-grounding conductor.
200 volts AC.
Second-degree burn.
15 feet off the ground.

6. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
600 volts.
Derive a neutral for grounding purposes.
Continuous.

7. 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.
Provides single-phase power to smaller loads such as lights - heaters - etc.
The capacitors should be discharged.
Transformers.

8. Compared to the secondary of a loaded - step-down transformer - the primary has...
A.C.
Lower current and higher voltage
The sum of the two capacitors.
Full-load - three-phase voltage.

9. 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?
Lower current and higher voltage
It provides good speed control.
No.6 AWG.
600 volts.

10. 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...
Derive a neutral for grounding purposes.
Draw less current.
The sum of the two capacitors.
Nearly constant.

11. At what rate should mouth-to-mouth resuscitation be applied?
The motor rotation is reversed.
12 to 15 times a minute.
Inductance.
X.

12. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Disconnect the frame-grounding conductor.
5:1.
The motor rotation is reversed.
Current that changes constantly in magnitude and periodically in direction.

13. A control power transformer...
No.6 AWG.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Shunted and taped
They should be made by the same manufacturer.

14. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
At least two phases
7 -630 volts.
Continuous.

15. The purpose of a zig-zag transformer is to...
The capacitors should be discharged.
Shunted and taped
A grounding resistor.
Derive a neutral for grounding purposes.

16. The primary leads of a single-phase transformer should be connected to the...
200 volts AC.
A.C.
Isolation transformer.
H terminals.

17. Not an acceptable method for the installations of surface transformers?
Derive a neutral for grounding purposes.
Inductance.
They must be installed at least 7 feet above the ground.
Second-degree burn.

18. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
They must be installed at least 7 feet above the ground.
Alternating current.
277 volts.
The capacitors should be discharged.

19. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
The capacitors should be discharged.
Full-load - three-phase voltage.
1 amp.
Grounded phase and ground fault devices were not operating.

20. 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?
Provides single-phase power to smaller loads such as lights - heaters - etc.
At the source transformer.
3 -979 Volts.
15 feet off the ground.

21. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
5:1.
2000 watts
Allow for metering voltage and Current.

22. What is the danger when working around capacitors?
No.6 AWG.
An electrical shock hazard may exist.
Kilovolt ampere (KVA).
600 volts.

23. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
At least two phases
Larger than that found in the primary winding.
It provides good speed control.
They should be made by the same manufacturer.

24. 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?
It provides good speed control.
Transformers.
75 turns.
12 to 15 times a minute.

25. What steps up or steps down AC voltage?
The chest should rise or inflate.
Two speeds
Transformer
Grounded phase and ground fault devices were not operating.

26. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
At the source transformer.
Allow for metering voltage and Current.
Squirrel-cage induction motor.
277 volts.

27. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
3 -979 Volts.
Check to make sure that the victim is not still in contact with the electricity.
An electrical shock hazard may exist.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

28. Under fault conditions - the grounding resistor in a high voltage circuit limits the voltage drop in the grounding circuit external to the resistor to not more than...
Full-load - three-phase voltage.
Isolation transformer.
100 volts.
Nearly constant.

29. A burn causing a blister is classified as a...
480 volts.
Transformers.
No.6 AWG.
Second-degree burn.

30. How do you change the direction of a 3-phase AC motor?
60 cycles per second (60 Hertz).
3 -979 Volts.
12 to 15 times a minute.
Reverse any two-phase leads.

31. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Provides single-phase power to smaller loads such as lights - heaters - etc.
A step-up transformer.
Grounded phase and ground fault devices were not operating.
Draw less current.

32. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
3 -979 Volts.
Disconnect the frame-grounding conductor.
Check to make sure that the victim is not still in contact with the electricity.
Continuous.

33. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
H terminals.
Shunted and taped
Squirrel-cage rotor.

34. Not a symptom of electrical shock?.
It provides good speed control.
75 turns.
Hyperventilation.
They should be made by the same manufacturer.

35. Not true about AC power?
H terminals.
At the source transformer.
It provides good speed control.
Transformers.

36. High voltage is used to transmit power over long distances...
480 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
Cut around clothing that has adhered to the burned area.
They must be installed at least 7 feet above the ground.

37. What should the duty rating of a grounding resistor be?
Continuous.
The capacitors should be discharged.
Transformer
An electrical shock hazard may exist.

38. 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.
Lower current and higher voltage
Hyperventilation.
Derive a neutral for grounding purposes.

39. Compared to the secondary of a loaded - step-down transformer - the primary has...
Shunted and taped
Inductance.
Current changing constantly in magnitude and periodically in direction.
Lower current and higher voltage.

40. The standard frequency of power supplied by the power company is...
Lower current and higher voltage.
They should be made by the same manufacturer.
60 cycles per second (60 Hertz).
Reverse its rotation.

41. 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?
Second-degree burn.
Because less current flowing at high voltage causes less line loss per kilowatt.
150 turns.
Disconnect the frame-grounding conductor.

42. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
15 feet off the ground.
1 amp.
Inductance.
Squirrel-cage rotor.

43. A transformer with a 1:1 ratio is usually a (an)...
Inductance.
Full-load - three-phase voltage.
Isolation transformer.
At least two phases

44. 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?
Cut around clothing that has adhered to the burned area.
800 volts.
Kilovolt ampere (KVA).
Lower current and higher voltage.

45. Current in an AC circuit may be measured by...
The capacitors should be discharged.
Clamp-on ammeter.
Two speeds
100 turns.

46. Define alternating current...
3 -979 Volts.
7 -630 volts.
Current changing constantly in magnitude and periodically in direction.
2000 watts

47. AC voltage is raised or lowered by means of...
Nearly constant.
The current will read zero.
Because less current flowing at high voltage causes less line loss per kilowatt.
Transformers.

48. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Four times less than that of the secondary.
The motor rotation is reversed.
The chest should rise or inflate.
Continuous.

49. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
The capacitors should be discharged.
2000 watts
Kilovolt ampere (KVA).
It provides good speed control.

50. The property of an electrical circuit that opposes any change in voltage is called...
Carotid pulse - which is located in the neck next to the Adam's apple.
Capacitance.
Lower current and higher voltage.
Provides single-phase power to smaller loads such as lights - heaters - etc.

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AC Theory

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