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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. All transformers step voltage up or down by...
Clamp-on ammeter.
Inductance.
60 Hertz
Lower current and higher voltage.

2. What should the duty rating of a grounding resistor be?
277 volts.
Transformers.
Continuous.
Hyperventilation.

3. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
5:1.
200 volts AC.
7 -630 volts.

4. Alternating current may be defined as...
Inductance.
Current that changes constantly in magnitude and periodically in direction.
Lower current and higher voltage.
800 volts.

5. Not a symptom of electrical shock?.
Current that changes constantly in magnitude and periodically in direction.
Tied together
Grounded phase and ground fault devices were not operating.
Hyperventilation.

6. Compared to the secondary of a loaded - step-down transformer - the primary has...
The sum of the two capacitors.
The motor rotation is reversed.
Full-load - three-phase voltage.
Lower current and higher voltage.

7. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
12 to 15 times a minute.
Check to make sure that the victim is not still in contact with the electricity.
Derive a neutral for grounding purposes.
25 feet.

8. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
Cut around clothing that has adhered to the burned area.
Reverse its rotation.
An electromagnet.

9. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Four times less than that of the secondary.
Two speeds
60 cycles per second (60 Hertz).

10. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Larger than that found in the primary winding.
7 -630 volts.
Allow for metering voltage and Current.
Tied together

11. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
A step-up transformer.
Derive a neutral for grounding purposes.
150 turns.

12. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Stator windings.
15 feet off the ground.
Derive a neutral for grounding purposes.
100 volts.

13. 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.
Cut around clothing that has adhered to the burned area.
75 turns.
60 cycles per second (60 Hertz).
5:1

14. 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.
Draw less current.
100 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.

15. Not true about AC power?
Potential transformer.
Lower current and higher voltage.
It provides good speed control.
A.C.

16. The speed of an alternating current - squirrel-cage induction motor is...
X.
Nearly constant.
Derive a neutral for grounding purposes.
Stator windings.

17. 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...
Circuit Breaker.
Transformer
100 volts.
Clamp-on ammeter.

18. 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.
Lower current and higher voltage.
Inductance.
The chest should rise or inflate.

19. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
Potential transformer.
No.6 AWG.
3 -979 Volts.

20. What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
Allow for metering voltage and Current.
100 turns.
Isolation transformer.

21. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Because less current flowing at high voltage causes less line loss per kilowatt.
75 turns.
Electro-magnetism for their operation.

22. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Current changing constantly in magnitude and periodically in direction.
Kilovolt ampere (KVA).
Grounded phase and ground fault devices were not operating.
800 volts.

23. What type motor is a wound-rotor induction motor?
An electrical shock hazard may exist.
200 volts AC.
The capacitors should be discharged.
A.C.

24. What is a capacitor?
A grounding resistor.
Draw less current.
A device used to store electrical energy.
Shunted and taped

25. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
600 volts.
Two speeds
Larger than that found in the primary winding.
Four times less than that of the secondary.

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.
The capacitors should be discharged.
Draw less current.
15 feet off the ground.

27. At what rate should mouth-to-mouth resuscitation be applied?
Isolation transformer.
At the source transformer.
Squirrel-cage induction motor.
12 to 15 times a minute.

28. What type of 3-phase AC motor is used most often around a mine?
Transformer
Squirrel-cage induction motor.
Shunted and taped
Circuit Breaker.

29. Current that changes periodically in direction is...
12 to 15 times a minute.
Alternating current.
Carotid pulse - which is located in the neck next to the Adam's apple.
Shunted and taped

30. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Reverse its rotation.
277 volts.
5:1

31. 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?
Clamp-on ammeter.
Stator windings.
It provides good speed control.
100 turns.

32. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Tied together
Kilovolt ampere (KVA).
Short-circuited after power has been removed.
Alternating current.

33. How should clothing be removed from a burn?
They must be installed at least 7 feet above the ground.
Nearly constant.
Cut around clothing that has adhered to the burned area.
Draw less current.

34. What steps up or steps down AC voltage?
Shunted and taped
Transformer
Provides single-phase power to smaller loads such as lights - heaters - etc.
An electrical shock hazard may exist.

35. The primary leads of a single-phase transformer should be connected to the...
A step-up transformer.
Nearly constant.
Draw less current.
H terminals.

36. 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?
Carotid pulse - which is located in the neck next to the Adam's apple.
The current will read zero.
800 volts.
A step-up transformer.

37. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Isolation transformer.
75 turns.
Two speeds
2000 watts

38. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Isolation transformer.
It provides good speed control.
480 volts.
A step-up transformer.

39. The secondary windings on a 10:1 step-down transformer will have a wire size...
Four times less than that of the secondary.
Isolation transformer.
Larger than that found in the primary winding.
Capacitance.

40. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
The current will read zero.
2000 watts
It provides good speed control.

41. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Four times less than that of the secondary.
Circuit Breaker.
The current will read zero.
1 amp.

42. A solenoid coil is...
Grounded phase and ground fault devices were not operating.
An electromagnet.
Larger than that found in the primary winding.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

43. High voltage is used to transmit power over long distances...
600 volts.
Full-load - three-phase voltage.
Grounded phase and ground fault devices were not operating.
Because less current flowing at high voltage causes less line loss per kilowatt.

44. A transformer with a 1:1 ratio is usually a (an)...
Full-load - three-phase voltage.
Disconnect the frame-grounding conductor.
The current will read zero.
Isolation transformer.

45. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Inductance.
480 volts.
Capacitance.

46. The property of an electrical circuit that opposes any change in voltage is called...
Full-load - three-phase voltage.
Capacitance.
75 turns.
800 volts.

47. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Squirrel-cage rotor.
277 volts.
Short-circuited after power has been removed.
Reverse its rotation.

48. Where should grounding resistors be located?
At the source transformer.
Four times less than that of the secondary.
A.C.
600 volts.

49. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
800 volts.
150 turns.
The motor rotation is reversed.

50. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Inductance.
Two speeds
Electro-magnetism for their operation.