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AC Theory

Instructions:

Answer 50 questions in 15 minutes.
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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. If any two-phase wires are reversed on a three-phase motor - the motor will...
The capacitors should be discharged.
H terminals.
An electromagnet.
Reverse its rotation.

2. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Lower current and higher voltage
Short-circuited after power has been removed.
Cut around clothing that has adhered to the burned area.

3. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
2000 watts
480 volts.
Grounded phase and ground fault devices were not operating.
Zero amps.

4. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
150 turns.
Second-degree burn.
15 feet off the ground.
The chest should rise or inflate.

5. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
5:1
3 -979 Volts.
Draw less current.

6. Not a symptom of electrical shock?.
Current changing constantly in magnitude and periodically in direction.
They must be installed at least 7 feet above the ground.
Two speeds
Hyperventilation.

7. A control power transformer...
3 -979 Volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Transformers.
Capacitance.

8. The transformer used only to measure voltage is a...
They should be made by the same manufacturer.
A device used to store electrical energy.
Potential transformer.
Current changing constantly in magnitude and periodically in direction.

9. What position of a selector switch using a voltmeter would you select to check a 120-volt AC circuit to obtain the most accurate reading?
Reverse its rotation.
800 volts.
A.C.
200 volts AC.

10. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Short-circuited after power has been removed.
Transformers.
H terminals.

11. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
H terminals.
Shunted and taped
Draw less current.

12. AC voltage is raised or lowered by means of...
Nearly constant.
Draw less current.
Transformers.
60 Hertz

13. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Potential transformer.
They should be made by the same manufacturer.
Isolation transformer.
No.6 AWG.

14. What is the danger when working around capacitors?
Four times less than that of the secondary.
An electrical shock hazard may exist.
100 turns.
Disconnect the frame-grounding conductor.

15. What steps up or steps down AC voltage?
Transformer
The sum of the two capacitors.
Alternating current.
Squirrel-cage rotor.

16. Current in an AC circuit may be measured by...
Derive a neutral for grounding purposes.
Clamp-on ammeter.
Zero amps.
Stator windings.

17. What type motor is a wound-rotor induction motor?
15 feet off the ground.
Potential transformer.
A.C.
100 turns.

18. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
Because less current flowing at high voltage causes less line loss per kilowatt.
200 volts AC.
Carotid pulse - which is located in the neck next to the Adam's apple.

19. 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.
Clamp-on ammeter.
5:1.
Continuous.

20. The standard frequency of power supplied by the power company is...
Kilovolt ampere (KVA).
60 cycles per second (60 Hertz).
Nearly constant.
The motor rotation is reversed.

21. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Short-circuited after power has been removed.
The motor rotation is reversed.
Continuous.
150 turns.

22. The size of a transformer is measured in...
Shunted and taped
They must be installed at least 7 feet above the ground.
Kilovolt ampere (KVA).
An electromagnet.

23. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Circuit Breaker.
A step-up transformer.
5:1
The current will read zero.

24. 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.
Disconnect the frame-grounding conductor.
Carotid pulse - which is located in the neck next to the Adam's apple.
60 Hertz

25. 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?
Zero amps.
100 turns.
150 turns.
No.6 AWG.

26. A burn causing a blister is classified as a...
Second-degree burn.
12 to 15 times a minute.
Draw less current.
480 volts.

27. 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.
Allow for metering voltage and Current.
Kilovolt ampere (KVA).
Four times less than that of the secondary.

28. When not connected to a load - the secondary leads of a current transformer should be...
Stator windings.
Shunted and taped
Circuit Breaker.
A device used to store electrical energy.

29. 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?
Two speeds
The current will read zero.
600 volts.
60 Hertz

30. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
An electrical shock hazard may exist.
277 volts.
Circuit Breaker.

31. How should clothing be removed from a burn?
Reverse its rotation.
Current that changes constantly in magnitude and periodically in direction.
Allow for metering voltage and Current.
Cut around clothing that has adhered to the burned area.

32. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Current that changes constantly in magnitude and periodically in direction.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Zero amps.
Current changing constantly in magnitude and periodically in direction.

33. Current that changes periodically in direction is...
Alternating current.
Carotid pulse - which is located in the neck next to the Adam's apple.
A grounding resistor.
A step-up transformer.

34. All transformers step voltage up or down by...
Derive a neutral for grounding purposes.
At least two phases
Inductance.
60 Hertz

35. Current transformers - or CT's - are used to...
12 to 15 times a minute.
Larger than that found in the primary winding.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Continuous.

36. Operating coils - motors - transformers - relays and solenoids depend upon...
Draw less current.
The motor rotation is reversed.
Derive a neutral for grounding purposes.
Electro-magnetism for their operation.

37. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
It provides good speed control.
277 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Stator windings.

38. 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...
600 volts.
Shunted and taped
Draw less current.
Check to make sure that the victim is not still in contact with the electricity.

39. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
277 volts.
75 turns.
Clamp-on ammeter.

40. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
Alternating current.
12 to 15 times a minute.
75 turns.

41. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Inductance.
25 feet.
Squirrel-cage rotor.
Electro-magnetism for their operation.

42. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Second-degree burn.
200 volts AC.
A grounding resistor.
The motor rotation is reversed.

43. How do you change the direction of a 3-phase AC motor?
Four times less than that of the secondary.
Reverse any two-phase leads.
Allow for metering voltage and Current.
5:1.

44. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
The chest should rise or inflate.
Reverse any two-phase leads.
The motor rotation is reversed.

45. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
600 volts.
H terminals.
Because less current flowing at high voltage causes less line loss per kilowatt.

46. Where should grounding resistors be located?
At the source transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Circuit Breaker.
600 volts.

47. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
X.
Squirrel-cage rotor.
600 volts.

48. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
1 amp.
Clamp-on ammeter.
Squirrel-cage rotor.

49. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Second-degree burn.
1 amp.
X.
Two speeds

50. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
75 turns.
Draw less current.
15 feet off the ground.
A.C.

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AC Theory

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