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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. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
It provides good speed control.
5:1
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
12 to 15 times a minute.

2. The primary leads of a single-phase transformer should be connected to the...
Inductance.
Because less current flowing at high voltage causes less line loss per kilowatt.
Capacitance.
H terminals.

3. 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?
Current changing constantly in magnitude and periodically in direction.
A device used to store electrical energy.
600 volts.
Tied together

4. The property of an electrical circuit that opposes any change in voltage is called...
2000 watts
The chest should rise or inflate.
Capacitance.
75 turns.

5. 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?
75 turns.
The current will read zero.
100 turns.
2000 watts

6. The purpose of a zig-zag transformer is to...
The chest should rise or inflate.
Circuit Breaker.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Derive a neutral for grounding purposes.

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

8. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
Allow for metering voltage and Current.
2000 watts
600 volts.

9. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Nearly constant.
They must be installed at least 7 feet above the ground.
Check to make sure that the victim is not still in contact with the electricity.

10. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Current changing constantly in magnitude and periodically in direction.
The chest should rise or inflate.
200 volts AC.
Second-degree burn.

11. AC voltage is raised or lowered by means of...
Potential transformer.
Transformers.
Full-load - three-phase voltage.
Clamp-on ammeter.

12. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Kilovolt ampere (KVA).
Short-circuited after power has been removed.
15 feet off the ground.
Stator windings.

13. What should the duty rating of a grounding resistor be?
Continuous.
Short-circuited after power has been removed.
Electro-magnetism for their operation.
75 turns.

14. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
277 volts.
A step-up transformer.
7 -630 volts.
5:1.

15. 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?
Shunted and taped
75 turns.
It provides good speed control.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

16. What is a capacitor?
The current will read zero.
Allow for metering voltage and Current.
A device used to store electrical energy.
Transformers.

17. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Shunted and taped
A device used to store electrical energy.
Tied together

18. Compared to the secondary of a loaded - step-down transformer - the primary has...
12 to 15 times a minute.
Lower current and higher voltage.
No.6 AWG.
Alternating current.

19. How should clothing be removed from a burn?
600 volts.
Larger than that found in the primary winding.
Hyperventilation.
Cut around clothing that has adhered to the burned area.

20. 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...
Current that changes constantly in magnitude and periodically in direction.
12 to 15 times a minute.
Two speeds
Tied together

21. Where should grounding resistors be located?
At the source transformer.
Nearly constant.
Squirrel-cage rotor.
200 volts AC.

22. 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...
Draw less current.
Transformers.
15 feet off the ground.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

23. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Lower current and higher voltage
1 amp.
25 feet.

24. The standard frequency of alternating current used at a mine is...
At the source transformer.
60 Hertz
Four times less than that of the secondary.
The sum of the two capacitors.

25. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Current that changes constantly in magnitude and periodically in direction.
A grounding resistor.
25 feet.

26. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Isolation transformer.
75 turns.
Shunted and taped

27. Current in an AC circuit may be measured by...
Second-degree burn.
Clamp-on ammeter.
Electro-magnetism for their operation.
Lower current and higher voltage

28. 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.
An electromagnet.
Reverse any two-phase leads.
The sum of the two capacitors.

29. At what rate should mouth-to-mouth resuscitation be applied?
Stator windings.
Reverse its rotation.
7 -630 volts.
12 to 15 times a minute.

30. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Check to make sure that the victim is not still in contact with the electricity.
Hyperventilation.
X.
Grounded phase and ground fault devices were not operating.

31. Three-phase AC underground cables must be provided with overcurrent protection using a...
Full-load - three-phase voltage.
Circuit Breaker.
Short-circuited after power has been removed.
60 Hertz

32. All transformers step voltage up or down by...
Inductance.
Second-degree burn.
No.6 AWG.
150 turns.

33. Operating coils - motors - transformers - relays and solenoids depend upon...
Larger than that found in the primary winding.
A grounding resistor.
Electro-magnetism for their operation.
60 cycles per second (60 Hertz).

34. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
100 volts.
5:1.
800 volts.
Disconnect the frame-grounding conductor.

35. High voltage is used to transmit power over long distances...
They must be installed at least 7 feet above the ground.
Kilovolt ampere (KVA).
Because less current flowing at high voltage causes less line loss per kilowatt.
A.C.

36. A solenoid coil is...
60 cycles per second (60 Hertz).
Lower current and higher voltage.
Hyperventilation.
An electromagnet.

37. The transformer used only to measure voltage is a...
The motor rotation is reversed.
An electromagnet.
Potential transformer.
Larger than that found in the primary winding.

38. Which of the following does a squirrel cage induction motor have?
X.
7 -630 volts.
Clamp-on ammeter.
Stator windings.

39. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Derive a neutral for grounding purposes.
Larger than that found in the primary winding.
Zero amps.
Draw less current.

40. The secondary windings on a 10:1 step-down transformer will have a wire size...
277 volts.
Disconnect the frame-grounding conductor.
Grounded phase and ground fault devices were not operating.
Larger than that found in the primary winding.

41. The primary function of a power transformer is to provide...
25 feet.
3 -979 Volts.
Reverse any two-phase leads.
Full-load - three-phase voltage.

42. A wound-rotor induction motor has all the following EXCEPT...
12 to 15 times a minute.
Squirrel-cage rotor.
Circuit Breaker.
480 volts.

43. What is the danger when working around capacitors?
An electrical shock hazard may exist.
Continuous.
Inductance.
Squirrel-cage rotor.

44. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Zero amps.
Carotid pulse - which is located in the neck next to the Adam's apple.

45. Alternating current may be defined as...
Full-load - three-phase voltage.
Current that changes constantly in magnitude and periodically in direction.
Kilovolt ampere (KVA).
75 turns.

46. 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.
Provides single-phase power to smaller loads such as lights - heaters - etc.
5:1.
The current will read zero.
60 Hertz

47. 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.
A device used to store electrical energy.
A step-up transformer.
Zero amps.

48. The size of a transformer is measured in...
480 volts.
Kilovolt ampere (KVA).
Reverse any two-phase leads.
A device used to store electrical energy.

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 least two phases
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
No.6 AWG.
800 volts.

50. 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.
Inductance.
Isolation transformer.
Zero amps.