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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. Operating coils - motors - transformers - relays and solenoids depend upon...
A device used to store electrical energy.
Inductance.
Electro-magnetism for their operation.
An electrical shock hazard may exist.

2. AC voltage is raised or lowered by means of...
75 turns.
Disconnect the frame-grounding conductor.
They must be installed at least 7 feet above the ground.
Transformers.

3. How do you change the direction of a 3-phase AC motor?
An electrical shock hazard may exist.
Zero amps.
Reverse any two-phase leads.
Inductance.

4. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Tied together
277 volts.
Draw less current.
Electro-magnetism for their operation.

5. A burn causing a blister is classified as a...
Capacitance.
At least two phases
An electromagnet.
Second-degree burn.

6. A solenoid coil is...
Circuit Breaker.
Draw less current.
Lower current and higher voltage
An electromagnet.

7. A transformer with a 1:1 ratio is usually a (an)...
The current will read zero.
Cut around clothing that has adhered to the burned area.
Current changing constantly in magnitude and periodically in direction.
Isolation transformer.

8. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
Disconnect the frame-grounding conductor.
60 cycles per second (60 Hertz).
100 volts.

9. 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.
5:1
100 turns.
480 volts.
Derive a neutral for grounding purposes.

10. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Cut around clothing that has adhered to the burned area.
Short-circuited after power has been removed.
Because less current flowing at high voltage causes less line loss per kilowatt.
25 feet.

11. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Allow for metering voltage and Current.
They should be made by the same manufacturer.
Reverse its rotation.
A.C.

12. 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.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Because less current flowing at high voltage causes less line loss per kilowatt.
Transformer

13. A wound-rotor induction motor has all the following EXCEPT...
Circuit Breaker.
Nearly constant.
Derive a neutral for grounding purposes.
Squirrel-cage rotor.

14. The standard frequency of power supplied by the power company is...
Tied together
They must be installed at least 7 feet above the ground.
Inductance.
60 cycles per second (60 Hertz).

15. Where should grounding resistors be located?
Reverse any two-phase leads.
480 volts.
Current that changes constantly in magnitude and periodically in direction.
At the source transformer.

16. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Disconnect the frame-grounding conductor.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
5:1
Two speeds

17. What is a capacitor?
At least two phases
Squirrel-cage induction motor.
A device used to store electrical energy.
800 volts.

18. The property of an electric circuit that opposes any change in current is called...
3 -979 Volts.
7 -630 volts.
Inductance.
Two speeds

19. Three-phase AC underground cables must be provided with overcurrent protection using a...
No.6 AWG.
150 turns.
A step-up transformer.
Circuit Breaker.

20. 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?
Draw less current.
75 turns.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The sum of the two capacitors.

21. The property of an electrical circuit that opposes any change in voltage is called...
Cut around clothing that has adhered to the burned area.
Shunted and taped
Capacitance.
Clamp-on ammeter.

22. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Current changing constantly in magnitude and periodically in direction.
Circuit Breaker.
Grounded phase and ground fault devices were not operating.
A grounding resistor.

23. The secondary windings on a 10:1 step-down transformer will have a wire size...
Cut around clothing that has adhered to the burned area.
Larger than that found in the primary winding.
Potential transformer.
1 amp.

24. Define alternating current...
The capacitors should be discharged.
A step-up transformer.
Current changing constantly in magnitude and periodically in direction.
Transformers.

25. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
150 turns.
Inductance.
200 volts AC.

26. 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?
100 volts.
A.C.
75 turns.
Potential transformer.

27. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Larger than that found in the primary winding.
Provides single-phase power to smaller loads such as lights - heaters - etc.
15 feet off the ground.
Shunted and taped

28. Not a symptom of electrical shock?.
Hyperventilation.
Inductance.
Circuit Breaker.
75 turns.

29. Current transformers - or CT's - are used to...
277 volts.
Stator windings.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Current that changes constantly in magnitude and periodically in direction.

30. 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?
100 turns.
Hyperventilation.
Derive a neutral for grounding purposes.
200 volts AC.

31. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Draw less current.
Circuit Breaker.
Larger than that found in the primary winding.
The motor rotation is reversed.

32. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Shunted and taped
75 turns.
480 volts.
Stator windings.

33. Not true about AC power?
Inductance.
Full-load - three-phase voltage.
It provides good speed control.
Circuit Breaker.

34. Current that changes periodically in direction is...
Four times less than that of the secondary.
X.
H terminals.
Alternating current.

35. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Tied together
200 volts AC.
Second-degree burn.
No.6 AWG.

36. What is the danger when working around capacitors?
An electrical shock hazard may exist.
25 feet.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Current that changes constantly in magnitude and periodically in direction.

37. 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.
Potential transformer.
15 feet off the ground.
Circuit Breaker.

38. To protect against over-current in a three-phase circuit over-current protection must be provided for...
277 volts.
At least two phases
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
5:1

39. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Capacitance.
Zero amps.
800 volts.
Squirrel-cage induction motor.

40. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The sum of the two capacitors.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The chest should rise or inflate.
100 turns.

41. All transformers step voltage up or down by...
100 turns.
Zero amps.
7 -630 volts.
Inductance.

42. What should the duty rating of a grounding resistor be?
Four times less than that of the secondary.
Two speeds
Reverse its rotation.
Continuous.

43. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
An electrical shock hazard may exist.
Reverse any two-phase leads.
1 amp.
15 feet off the ground.

44. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Larger than that found in the primary winding.
Current changing constantly in magnitude and periodically in direction.
2000 watts
25 feet.

45. Which of the following does a squirrel cage induction motor have?
Stator windings.
1 amp.
Carotid pulse - which is located in the neck next to the Adam's apple.
Current changing constantly in magnitude and periodically in direction.

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

47. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Squirrel-cage rotor.
Reverse any two-phase leads.
X.
Isolation transformer.

48. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Grounded phase and ground fault devices were not operating.
Shunted and taped
Four times less than that of the secondary.
Second-degree burn.

49. The purpose of a zig-zag transformer is to...
25 feet.
Electro-magnetism for their operation.
Derive a neutral for grounding purposes.
75 turns.

50. The primary leads of a single-phase transformer should be connected to the...
At the source transformer.
Electro-magnetism for their operation.
12 to 15 times a minute.
H terminals.