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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. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Isolation transformer.
Current that changes constantly in magnitude and periodically in direction.
No.6 AWG.
Alternating current.

2. The property of an electrical circuit that opposes any change in voltage is called...
Lower current and higher voltage
Isolation transformer.
Capacitance.
Lower current and higher voltage.

3. What steps up or steps down AC voltage?
2000 watts
Transformer
Kilovolt ampere (KVA).
Second-degree burn.

4. A wound-rotor induction motor has all the following EXCEPT...
Two speeds
Alternating current.
Squirrel-cage rotor.
Provides single-phase power to smaller loads such as lights - heaters - etc.

5. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Hyperventilation.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Stator windings.

6. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Squirrel-cage rotor.
The capacitors should be discharged.
An electrical shock hazard may exist.
Short-circuited after power has been removed.

7. AC voltage is raised or lowered by means of...
Alternating current.
100 turns.
Transformers.
Draw less current.

8. Where should grounding resistors be located?
At the source transformer.
Draw less current.
A.C.
Potential transformer.

9. All transformers step voltage up or down by...
Clamp-on ammeter.
Second-degree burn.
Inductance.
Because less current flowing at high voltage causes less line loss per kilowatt.

10. 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...
Tied together
Inductance.
A device used to store electrical energy.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

11. 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.
A step-up transformer.
Capacitance.
60 cycles per second (60 Hertz).

12. What is a capacitor?
Squirrel-cage induction motor.
A device used to store electrical energy.
Zero amps.
Cut around clothing that has adhered to the burned area.

13. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Circuit Breaker.
7 -630 volts.
Current that changes constantly in magnitude and periodically in direction.
25 feet.

14. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Cut around clothing that has adhered to the burned area.
The motor rotation is reversed.
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.

15. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Transformers.
100 volts.
Electro-magnetism for their operation.

16. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
Disconnect the frame-grounding conductor.
Circuit Breaker.
15 feet off the ground.

17. Operating coils - motors - transformers - relays and solenoids depend upon...
Shunted and taped
Electro-magnetism for their operation.
277 volts.
7 -630 volts.

18. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
The current will read zero.
A device used to store electrical energy.
It provides good speed control.

19. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Kilovolt ampere (KVA).
480 volts.
Squirrel-cage rotor.
Full-load - three-phase voltage.

20. A burn causing a blister is classified as a...
Second-degree burn.
Kilovolt ampere (KVA).
100 turns.
Cut around clothing that has adhered to the burned area.

21. Three-phase AC underground cables must be provided with overcurrent protection using a...
Allow for metering voltage and Current.
Circuit Breaker.
Stator windings.
Alternating current.

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

23. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Inductance.
Short-circuited after power has been removed.
At least two phases

24. Alternating current may be defined as...
Full-load - three-phase voltage.
Tied together
Current that changes constantly in magnitude and periodically in direction.
60 cycles per second (60 Hertz).

25. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
15 feet off the ground.
Squirrel-cage induction motor.
Provides single-phase power to smaller loads such as lights - heaters - etc.

26. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
5:1
A.C.
Grounded phase and ground fault devices were not operating.
The current will read zero.

27. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Check to make sure that the victim is not still in contact with the electricity.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
1 amp.
600 volts.

28. Compared to the secondary of a loaded - step-down transformer - the primary has...
Draw less current.
Lower current and higher voltage.
Draw less current.
An electromagnet.

29. Not an acceptable method for the installations of surface transformers?
Allow for metering voltage and Current.
They must be installed at least 7 feet above the ground.
A step-up transformer.
3 -979 Volts.

30. When not connected to a load - the secondary leads of a current transformer should be...
Current that changes constantly in magnitude and periodically in direction.
Shunted and taped
800 volts.
Potential transformer.

31. The combined capacitance of two capacitors in parallel is...
Kilovolt ampere (KVA).
The sum of the two capacitors.
Grounded phase and ground fault devices were not operating.
Larger than that found in the primary winding.

32. 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?
800 volts.
Continuous.
Squirrel-cage induction motor.
150 turns.

33. The primary leads of a single-phase transformer should be connected to the...
Inductance.
H terminals.
Potential transformer.
Current that changes constantly in magnitude and periodically in direction.

34. A transformer with a 1:1 ratio is usually a (an)...
Electro-magnetism for their operation.
At least two phases
The capacitors should be discharged.
Isolation transformer.

35. 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?
75 turns.
Draw less current.
An electrical shock hazard may exist.
Continuous.

36. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
The chest should rise or inflate.
1 amp.
60 Hertz
A device used to store electrical energy.

37. The transformer used only to measure voltage is a...
Short-circuited after power has been removed.
Zero amps.
Potential transformer.
At least two phases

38. If any two-phase wires are reversed on a three-phase motor - the motor will...
5:1
Reverse its rotation.
60 Hertz
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

39. 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?
The sum of the two capacitors.
75 turns.
800 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.

40. 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...
100 turns.
100 volts.
Check to make sure that the victim is not still in contact with the electricity.
Cut around clothing that has adhered to the burned area.

41. How should clothing be removed from a burn?
Hyperventilation.
Allow for metering voltage and Current.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Cut around clothing that has adhered to the burned area.

42. How do you change the direction of a 3-phase AC motor?
Cut around clothing that has adhered to the burned area.
Reverse any two-phase leads.
7 -630 volts.
Derive a neutral for grounding purposes.

43. 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...
7 -630 volts.
Hyperventilation.
Transformer
Draw less current.

44. A solenoid coil is...
Lower current and higher voltage
An electromagnet.
The sum of the two capacitors.
Electro-magnetism for their operation.

45. The property of an electric circuit that opposes any change in current is called...
Lower current and higher voltage
A.C.
Inductance.
7 -630 volts.

46. What type motor is a wound-rotor induction motor?
A.C.
A step-up transformer.
12 to 15 times a minute.
The capacitors should be discharged.

47. The standard frequency of alternating current used at a mine is...
75 turns.
Electro-magnetism for their operation.
Check to make sure that the victim is not still in contact with the electricity.
60 Hertz

48. 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.
The current will read zero.
75 turns.
5:1
Allow for metering voltage and Current.

49. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
3 -979 Volts.
X.
Draw less current.
277 volts.

50. The size of a transformer is measured in...
Current that changes constantly in magnitude and periodically in direction.
Kilovolt ampere (KVA).
25 feet.
Because less current flowing at high voltage causes less line loss per kilowatt.