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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. 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.
Allow for metering voltage and Current.
It provides good speed control.
Two speeds

2. The primary leads of a single-phase transformer should be connected to the...
150 turns.
Current changing constantly in magnitude and periodically in direction.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
H terminals.

3. 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.
5:1.
100 volts.
800 volts.

4. Which of the following does a squirrel cage induction motor have?
Transformer
Isolation transformer.
Stator windings.
The motor rotation is reversed.

5. Three-phase AC underground cables must be provided with overcurrent protection using a...
They should be made by the same manufacturer.
Circuit Breaker.
75 turns.
Grounded phase and ground fault devices were not operating.

6. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Lower current and higher voltage.
The chest should rise or inflate.
60 Hertz
277 volts.

7. 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...
Larger than that found in the primary winding.
Nearly constant.
Carotid pulse - which is located in the neck next to the Adam's apple.
Tied together

8. The size of a transformer is measured in...
Zero amps.
Stator windings.
Kilovolt ampere (KVA).
Squirrel-cage induction motor.

9. What is the danger when working around capacitors?
An electrical shock hazard may exist.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Reverse any two-phase leads.
800 volts.

10. AC voltage is raised or lowered by means of...
5:1.
Transformers.
60 Hertz
100 volts.

11. 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?
12 to 15 times a minute.
800 volts.
The sum of the two capacitors.
Kilovolt ampere (KVA).

12. 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?
They should be made by the same manufacturer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
75 turns.
At least two phases

13. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
75 turns.
Clamp-on ammeter.
Cut around clothing that has adhered to the burned area.
X.

14. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A.C.
The current will read zero.
An electrical shock hazard may exist.

15. High voltage is used to transmit power over long distances...
Cut around clothing that has adhered to the burned area.
An electrical shock hazard may exist.
Because less current flowing at high voltage causes less line loss per kilowatt.
A.C.

16. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
3 -979 Volts.
2000 watts
75 turns.
X.

17. 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?
Allow for metering voltage and Current.
75 turns.
277 volts.
The current will read zero.

18. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
A.C.
They must be installed at least 7 feet above the ground.
No.6 AWG.
Reverse any two-phase leads.

19. 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?
Provides single-phase power to smaller loads such as lights - heaters - etc.
200 volts AC.
12 to 15 times a minute.
An electrical shock hazard may exist.

20. The main function of CT's and PT's on a main substation is to...
Two speeds
Grounded phase and ground fault devices were not operating.
Transformer
Allow for metering voltage and Current.

21. The secondary windings on a 10:1 step-down transformer will have a wire size...
Circuit Breaker.
Inductance.
Larger than that found in the primary winding.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

22. Operating coils - motors - transformers - relays and solenoids depend upon...
A device used to store electrical energy.
Zero amps.
Electro-magnetism for their operation.
Reverse any two-phase leads.

23. Define alternating current...
Kilovolt ampere (KVA).
60 Hertz
Current changing constantly in magnitude and periodically in direction.
Isolation transformer.

24. 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.
A.C.
Current changing constantly in magnitude and periodically in direction.
Clamp-on ammeter.

25. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
An electromagnet.
Capacitance.
25 feet.
Hyperventilation.

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.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Hyperventilation.
Reverse its rotation.

27. 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?
They should be made by the same manufacturer.
600 volts.
Allow for metering voltage and Current.
Draw less current.

28. What should the duty rating of a grounding resistor be?
Nearly constant.
Continuous.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Potential transformer.

29. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
Current that changes constantly in magnitude and periodically in direction.
Inductance.
No.6 AWG.

30. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Because less current flowing at high voltage causes less line loss per kilowatt.
Hyperventilation.
At least two phases
75 turns.

31. 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...
X.
100 volts.
An electrical shock hazard may exist.
Hyperventilation.

32. Not an acceptable method for the installations of surface transformers?
Potential transformer.
Transformers.
They must be installed at least 7 feet above the ground.
Allow for metering voltage and Current.

33. 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?
Inductance.
100 turns.
15 feet off the ground.
Grounded phase and ground fault devices were not operating.

34. The speed of an alternating current - squirrel-cage induction motor is...
The capacitors should be discharged.
12 to 15 times a minute.
Nearly constant.
150 turns.

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

36. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
Capacitance.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Electro-magnetism for their operation.

37. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Full-load - three-phase voltage.
60 Hertz
5:1
The capacitors should be discharged.

38. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage rotor.
Squirrel-cage induction motor.
2000 watts
Two speeds

39. A wound-rotor induction motor has all the following EXCEPT...
The motor rotation is reversed.
7 -630 volts.
Squirrel-cage rotor.
Current changing constantly in magnitude and periodically in direction.

40. Current in an AC circuit may be measured by...
100 turns.
Short-circuited after power has been removed.
Clamp-on ammeter.
A device used to store electrical energy.

41. The property of an electrical circuit that opposes any change in voltage is called...
Reverse any two-phase leads.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Check to make sure that the victim is not still in contact with the electricity.
Capacitance.

42. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Grounded phase and ground fault devices were not operating.
An electromagnet.
Reverse any two-phase leads.
200 volts AC.

43. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Draw less current.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Lower current and higher voltage.
15 feet off the ground.

44. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
At the source transformer.
Inductance.
Short-circuited after power has been removed.
Nearly constant.

45. Current that changes periodically in direction is...
Alternating current.
1 amp.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
7 -630 volts.

46. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
150 turns.
Inductance.
Short-circuited after power has been removed.

47. The property of an electric circuit that opposes any change in current is called...
Cut around clothing that has adhered to the burned area.
Inductance.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
7 -630 volts.

48. Not true about AC power?
It provides good speed control.
100 volts.
The chest should rise or inflate.
Zero amps.

49. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
A device used to store electrical energy.
Four times less than that of the secondary.
Second-degree burn.
Two speeds

50. Not a symptom of electrical shock?.
Squirrel-cage rotor.
Draw less current.
A step-up transformer.
Hyperventilation.