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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 steps up or steps down AC voltage?
480 volts.
An electrical shock hazard may exist.
Transformer
A step-up transformer.

2. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Reverse its rotation.
The current will read zero.
Cut around clothing that has adhered to the burned area.
Larger than that found in the primary winding.

3. The standard frequency of alternating current used at a mine is...
An electrical shock hazard may exist.
60 Hertz
5:1
Clamp-on ammeter.

4. Which of the following does a squirrel cage induction motor have?
Stator windings.
H terminals.
The current will read zero.
Draw less current.

5. What is the first step to be followed in aiding a victim of electrical shock?
150 turns.
Capacitance.
600 volts.
Check to make sure that the victim is not still in contact with the electricity.

6. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
At least two phases
An electrical shock hazard may exist.
Two speeds

7. Three-phase AC underground cables must be provided with overcurrent protection using a...
15 feet off the ground.
Shunted and taped
Clamp-on ammeter.
Circuit Breaker.

8. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Allow for metering voltage and Current.
Nearly constant.
Check to make sure that the victim is not still in contact with the electricity.
The motor rotation is reversed.

9. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
A.C.
No.6 AWG.
Reverse any two-phase leads.
277 volts.

10. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Nearly constant.
The chest should rise or inflate.
Current changing constantly in magnitude and periodically in direction.

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

12. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Disconnect the frame-grounding conductor.
Inductance.
1 amp.
H terminals.

13. 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.
Zero amps.
75 turns.
Larger than that found in the primary winding.

14. Compared to the secondary of a loaded - step-down transformer - the primary has...
They must be installed at least 7 feet above the ground.
The sum of the two capacitors.
Lower current and higher voltage.
At the source transformer.

15. The property of an electrical circuit that opposes any change in voltage is called...
Clamp-on ammeter.
Transformers.
At least two phases
Capacitance.

16. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Alternating current.
Reverse any two-phase leads.
Short-circuited after power has been removed.
Full-load - three-phase voltage.

17. The standard frequency of power supplied by the power company is...
2000 watts
Provides single-phase power to smaller loads such as lights - heaters - etc.
60 cycles per second (60 Hertz).
Transformers.

18. At what rate should mouth-to-mouth resuscitation be applied?
800 volts.
100 volts.
12 to 15 times a minute.
100 turns.

19. Compared to the secondary of a loaded - step-down transformer - the primary has...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Four times less than that of the secondary.
Lower current and higher voltage
277 volts.

20. 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.
Draw less current.
An electromagnet.
Transformer

21. Operating coils - motors - transformers - relays and solenoids depend upon...
75 turns.
Electro-magnetism for their operation.
No.6 AWG.
Provides single-phase power to smaller loads such as lights - heaters - etc.

22. 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.
60 cycles per second (60 Hertz).
800 volts.
Transformer

23. The combined capacitance of two capacitors in parallel is...
480 volts.
Lower current and higher voltage
Because less current flowing at high voltage causes less line loss per kilowatt.
The sum of the two capacitors.

24. 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?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Squirrel-cage induction motor.
600 volts.
An electromagnet.

25. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
100 turns.
Grounded phase and ground fault devices were not operating.
7 -630 volts.
Zero amps.

26. A burn causing a blister is classified as a...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
277 volts.
Second-degree burn.
Reverse any two-phase leads.

27. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Grounded phase and ground fault devices were not operating.
No.6 AWG.

28. When not connected to a load - the secondary leads of a current transformer should be...
Tied together
An electromagnet.
The motor rotation is reversed.
Shunted and taped

29. The main function of CT's and PT's on a main substation is to...
The current will read zero.
They must be installed at least 7 feet above the ground.
Allow for metering voltage and Current.
Second-degree burn.

30. What type motor is a wound-rotor induction motor?
A.C.
25 feet.
No.6 AWG.
Two speeds

31. 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.
Capacitance.
At the source transformer.
A device used to store electrical energy.
5:1

32. 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 step-up transformer.
A grounding resistor.
Draw less current.

33. 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?
The current will read zero.
75 turns.
Tied together
Lower current and higher voltage.

34. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
The chest should rise or inflate.
15 feet off the ground.
Larger than that found in the primary winding.
Capacitance.

35. What is the danger when working around capacitors?
Tied together
An electrical shock hazard may exist.
H terminals.
A step-up transformer.

36. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
100 turns.
An electromagnet.
The capacitors should be discharged.
Reverse any two-phase leads.

37. All transformers step voltage up or down by...
Short-circuited after power has been removed.
Inductance.
7 -630 volts.
Allow for metering voltage and Current.

38. What type of 3-phase AC motor is used most often around a mine?
Cut around clothing that has adhered to the burned area.
At least two phases
150 turns.
Squirrel-cage induction motor.

39. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
No.6 AWG.
75 turns.
Stator windings.

40. A wound-rotor induction motor has all the following EXCEPT...
Lower current and higher voltage.
X.
The sum of the two capacitors.
Squirrel-cage rotor.

41. Not true about AC power?
60 cycles per second (60 Hertz).
It provides good speed control.
200 volts AC.
Second-degree burn.

42. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Potential transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Current changing constantly in magnitude and periodically in direction.

43. 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.
Two speeds
100 turns.
Transformers.
5:1.

44. If any two-phase wires are reversed on a three-phase motor - the motor will...
The current will read zero.
60 Hertz
Reverse its rotation.
The motor rotation is reversed.

45. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
A device used to store electrical energy.
Continuous.
200 volts AC.
X.

46. The transformer used only to measure voltage is a...
Transformer
Squirrel-cage induction motor.
Potential transformer.
Electro-magnetism for their operation.

47. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Nearly constant.
Squirrel-cage induction motor.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Lower current and higher voltage

48. 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?
100 turns.
Shunted and taped
15 feet off the ground.
Squirrel-cage induction motor.

49. 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?
At the source transformer.
Kilovolt ampere (KVA).
800 volts.
Full-load - three-phase voltage.

50. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Draw less current.
600 volts.
Kilovolt ampere (KVA).
Disconnect the frame-grounding conductor.