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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 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?
480 volts.
100 turns.
Transformers.
The capacitors should be discharged.

2. 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?
Provides single-phase power to smaller loads such as lights - heaters - etc.
The motor rotation is reversed.
150 turns.
Electro-magnetism for their operation.

3. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
It provides good speed control.
Grounded phase and ground fault devices were not operating.
Squirrel-cage rotor.

4. A burn causing a blister is classified as a...
Check to make sure that the victim is not still in contact with the electricity.
Second-degree burn.
At the source transformer.
Transformer

5. 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.
Shunted and taped
Potential transformer.
25 feet.

6. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
200 volts AC.
No.6 AWG.
5:1.
Allow for metering voltage and Current.

7. High voltage is used to transmit power over long distances...
Full-load - three-phase voltage.
Disconnect the frame-grounding conductor.
Because less current flowing at high voltage causes less line loss per kilowatt.
Four times less than that of the secondary.

8. What should the duty rating of a grounding resistor be?
Continuous.
Short-circuited after power has been removed.
100 turns.
Squirrel-cage rotor.

9. Alternating current may be defined as...
H terminals.
A.C.
Current that changes constantly in magnitude and periodically in direction.
Reverse its rotation.

10. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Reverse its rotation.
Larger than that found in the primary winding.
Isolation transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

11. AC voltage is raised or lowered by means of...
Full-load - three-phase voltage.
Transformers.
Inductance.
The capacitors should be discharged.

12. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
200 volts AC.
Lower current and higher voltage.
Stator windings.

13. The standard frequency of alternating current used at a mine is...
Inductance.
60 Hertz
Short-circuited after power has been removed.
Draw less current.

14. 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...
Draw less current.
Derive a neutral for grounding purposes.
Lower current and higher voltage.
At least two phases

15. The transformer used only to measure voltage is a...
Potential transformer.
Larger than that found in the primary winding.
Reverse any two-phase leads.
A device used to store electrical energy.

16. At what rate should mouth-to-mouth resuscitation be applied?
Alternating current.
X.
12 to 15 times a minute.
1 amp.

17. The size of a transformer is measured in...
Kilovolt ampere (KVA).
25 feet.
The capacitors should be discharged.
Short-circuited after power has been removed.

18. All transformers step voltage up or down by...
Inductance.
Larger than that found in the primary winding.
Draw less current.
No.6 AWG.

19. A transformer with a 1:1 ratio is usually a (an)...
Alternating current.
The capacitors should be discharged.
Shunted and taped
Isolation transformer.

20. Not true about AC power?
The chest should rise or inflate.
25 feet.
It provides good speed control.
Shunted and taped

21. 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.
2000 watts
75 turns.
Inductance.

22. Current in an AC circuit may be measured by...
100 volts.
The motor rotation is reversed.
Clamp-on ammeter.
Circuit Breaker.

23. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Lower current and higher voltage
Squirrel-cage induction motor.
Grounded phase and ground fault devices were not operating.

24. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Nearly constant.
Cut around clothing that has adhered to the burned area.
Zero amps.

25. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
3 -979 Volts.
Lower current and higher voltage.
The capacitors should be discharged.
Derive a neutral for grounding purposes.

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

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27. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
75 turns.
2000 watts
60 cycles per second (60 Hertz).
277 volts.

28. 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.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A grounding resistor.
5:1
Full-load - three-phase voltage.

29. Not a symptom of electrical shock?.
277 volts.
Hyperventilation.
Clamp-on ammeter.
The sum of the two capacitors.

30. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Lower current and higher voltage
Draw less current.
Four times less than that of the secondary.
60 Hertz

31. How do you change the direction of a 3-phase AC motor?
Squirrel-cage induction motor.
Inductance.
Reverse any two-phase leads.
Larger than that found in the primary winding.

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?
200 volts AC.
600 volts.
Current changing constantly in magnitude and periodically in direction.
The capacitors should be discharged.

33. The primary leads of a single-phase transformer should be connected to the...
Provides single-phase power to smaller loads such as lights - heaters - etc.
H terminals.
5:1.
Zero amps.

34. When not connected to a load - the secondary leads of a current transformer should be...
Allow for metering voltage and Current.
An electrical shock hazard may exist.
Current changing constantly in magnitude and periodically in direction.
Shunted and taped

35. The speed of an alternating current - squirrel-cage induction motor is...
Squirrel-cage induction motor.
Carotid pulse - which is located in the neck next to the Adam's apple.
Short-circuited after power has been removed.
Nearly constant.

36. A control power transformer...
At least two phases
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Electro-magnetism for their operation.

37. 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...
Disconnect the frame-grounding conductor.
Two speeds
25 feet.
Tied together

38. Current that changes periodically in direction is...
Alternating current.
Lower current and higher voltage
2000 watts
Derive a neutral for grounding purposes.

39. What is a capacitor?
Electro-magnetism for their operation.
A device used to store electrical energy.
No.6 AWG.
Potential transformer.

40. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Cut around clothing that has adhered to the burned area.
12 to 15 times a minute.
A step-up transformer.
15 feet off the ground.

41. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Potential transformer.
They should be made by the same manufacturer.
Inductance.
The capacitors should be discharged.

42. The property of an electric circuit that opposes any change in current is called...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Transformer
Inductance.
5:1

43. Where should grounding resistors be located?
7 -630 volts.
Lower current and higher voltage
At the source transformer.
Second-degree burn.

44. The main function of CT's and PT's on a main substation is to...
7 -630 volts.
150 turns.
75 turns.
Allow for metering voltage and Current.

45. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
75 turns.
100 turns.
The sum of the two capacitors.

46. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
A.C.
Grounded phase and ground fault devices were not operating.
Lower current and higher voltage
Capacitance.

47. 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.
Kilovolt ampere (KVA).
The motor rotation is reversed.
Draw less current.

48. The standard frequency of power supplied by the power company is...
X.
Lower current and higher voltage
Tied together
60 cycles per second (60 Hertz).

49. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Two speeds
The chest should rise or inflate.
3 -979 Volts.
They should be made by the same manufacturer.

50. 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?
200 volts AC.
Zero amps.
Allow for metering voltage and Current.
Two speeds

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AC Theory

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