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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. A wound-rotor induction motor has all the following EXCEPT...
Because less current flowing at high voltage causes less line loss per kilowatt.
Squirrel-cage rotor.
Continuous.
At least two phases

2. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Transformer
They must be installed at least 7 feet above the ground.
15 feet off the ground.
Tied together

3. 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.
Transformer
60 cycles per second (60 Hertz).
Carotid pulse - which is located in the neck next to the Adam's apple.
5:1.

4. What type of 3-phase AC motor is used most often around a mine?
The capacitors should be discharged.
Kilovolt ampere (KVA).
3 -979 Volts.
Squirrel-cage induction motor.

5. The property of an electric circuit that opposes any change in current is called...
Inductance.
The chest should rise or inflate.
Squirrel-cage rotor.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

6. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Inductance.
Inductance.
They must be installed at least 7 feet above the ground.

7. Where should grounding resistors be located?
A.C.
Current that changes constantly in magnitude and periodically in direction.
Alternating current.
At the source transformer.

8. What should the duty rating of a grounding resistor be?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Continuous.
200 volts AC.
600 volts.

9. A control power transformer...
Nearly constant.
The current will read zero.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Provides single-phase power to smaller loads such as lights - heaters - etc.

10. Compared to the secondary of a loaded - step-down transformer - the primary has...
The sum of the two capacitors.
Lower current and higher voltage
100 volts.
60 cycles per second (60 Hertz).

11. A solenoid coil is...
An electromagnet.
H terminals.
Carotid pulse - which is located in the neck next to the Adam's apple.
The motor rotation is reversed.

12. Current transformers - or CT's - are used to...
600 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Stator windings.
Draw less current.

13. Which of the following does a squirrel cage induction motor have?
75 turns.
Stator windings.
The chest should rise or inflate.
75 turns.

14. The purpose of a zig-zag transformer is to...
Isolation transformer.
Derive a neutral for grounding purposes.
Capacitance.
100 turns.

15. Alternating current may be defined as...
Kilovolt ampere (KVA).
Draw less current.
Current that changes constantly in magnitude and periodically in direction.
Transformer

16. AC voltage is raised or lowered by means of...
Draw less current.
Electro-magnetism for their operation.
Transformers.
The current will read zero.

17. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
It provides good speed control.
No.6 AWG.
Nearly constant.

18. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
They must be installed at least 7 feet above the ground.
H terminals.
480 volts.
A step-up transformer.

19. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Electro-magnetism for their operation.
Transformer
Reverse any two-phase leads.
25 feet.

20. Not a symptom of electrical shock?.
Hyperventilation.
Draw less current.
Second-degree burn.
The sum of the two capacitors.

21. 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?
600 volts.
800 volts.
Check to make sure that the victim is not still in contact with the electricity.
At least two phases

22. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Draw less current.
150 turns.
X.
No.6 AWG.

23. What is the first step to be followed in aiding a victim of electrical shock?
Squirrel-cage induction motor.
Lower current and higher voltage.
Check to make sure that the victim is not still in contact with the electricity.
Draw less current.

24. 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.
277 volts.
Circuit Breaker.
600 volts.

25. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
2000 watts
They should be made by the same manufacturer.
Transformer

26. 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.
Four times less than that of the secondary.
Reverse any two-phase leads.
Lower current and higher voltage.

27. 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 volts.
Draw less current.
Clamp-on ammeter.
The current will read zero.

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

29. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
7 -630 volts.
Squirrel-cage rotor.
Carotid pulse - which is located in the neck next to the Adam's apple.
1 amp.

30. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
They should be made by the same manufacturer.
The motor rotation is reversed.
A grounding resistor.

31. Not true about AC power?
Hyperventilation.
It provides good speed control.
Grounded phase and ground fault devices were not operating.
800 volts.

32. The standard frequency of alternating current used at a mine is...
Squirrel-cage induction motor.
The sum of the two capacitors.
Short-circuited after power has been removed.
60 Hertz

33. The main function of CT's and PT's on a main substation is to...
277 volts.
3 -979 Volts.
Allow for metering voltage and Current.
Grounded phase and ground fault devices were not operating.

34. High voltage is used to transmit power over long distances...
60 Hertz
A grounding resistor.
The sum of the two capacitors.
Because less current flowing at high voltage causes less line loss per kilowatt.

35. What steps up or steps down AC voltage?
480 volts.
Transformer
Check to make sure that the victim is not still in contact with the electricity.
600 volts.

36. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Nearly constant.
Squirrel-cage rotor.
Disconnect the frame-grounding conductor.
800 volts.

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

38. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
At the source transformer.
They should be made by the same manufacturer.
Inductance.
7 -630 volts.

39. 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?
Larger than that found in the primary winding.
3 -979 Volts.
At the source transformer.
150 turns.

40. 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?
75 turns.
Squirrel-cage induction motor.
Lower current and higher voltage.
Continuous.

41. The secondary windings on a 10:1 step-down transformer will have a wire size...
Squirrel-cage rotor.
They must be installed at least 7 feet above the ground.
Lower current and higher voltage.
Larger than that found in the primary winding.

42. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
150 turns.
100 turns.
2000 watts
Two speeds

43. Operating coils - motors - transformers - relays and solenoids depend upon...
Second-degree burn.
Electro-magnetism for their operation.
Inductance.
Current that changes constantly in magnitude and periodically in direction.

44. 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?
Full-load - three-phase voltage.
150 turns.
Capacitance.
Check to make sure that the victim is not still in contact with the electricity.

45. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
2000 watts
Four times less than that of the secondary.
X.
Grounded phase and ground fault devices were not operating.

46. Three-phase AC underground cables must be provided with overcurrent protection using a...
Grounded phase and ground fault devices were not operating.
15 feet off the ground.
Circuit Breaker.
Derive a neutral for grounding purposes.

47. At what rate should mouth-to-mouth resuscitation be applied?
No.6 AWG.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
12 to 15 times a minute.
Provides single-phase power to smaller loads such as lights - heaters - etc.

48. Compared to the secondary of a loaded - step-down transformer - the primary has...
Current that changes constantly in magnitude and periodically in direction.
Lower current and higher voltage.
Shunted and taped
800 volts.

49. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
7 -630 volts.
480 volts.
X.
They must be installed at least 7 feet above the ground.

50. The size of a transformer is measured in...
Electro-magnetism for their operation.
5:1.
Kilovolt ampere (KVA).
75 turns.