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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...
It provides good speed control.
60 Hertz
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Electro-magnetism for their operation.

2. Not a symptom of electrical shock?.
Second-degree burn.
Check to make sure that the victim is not still in contact with the electricity.
12 to 15 times a minute.
Hyperventilation.

3. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
75 turns.
Second-degree burn.
Current changing constantly in magnitude and periodically in direction.

4. 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?
15 feet off the ground.
An electromagnet.
800 volts.
A device used to store electrical energy.

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

6. The speed of an alternating current - squirrel-cage induction motor is...
At least two phases
Squirrel-cage rotor.
Cut around clothing that has adhered to the burned area.
Nearly constant.

7. The standard frequency of alternating current used at a mine is...
75 turns.
60 Hertz
The capacitors should be discharged.
It provides good speed control.

8. 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?
Two speeds
Continuous.
15 feet off the ground.
75 turns.

9. Current transformers - or CT's - are used to...
An electrical shock hazard may exist.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Shunted and taped

10. What should the duty rating of a grounding resistor be?
Continuous.
At least two phases
Four times less than that of the secondary.
They should be made by the same manufacturer.

11. What is the danger when working around capacitors?
An electrical shock hazard may exist.
At the source transformer.
75 turns.
Current that changes constantly in magnitude and periodically in direction.

12. 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.
5:1.
No.6 AWG.
Full-load - three-phase voltage.
75 turns.

13. All transformers step voltage up or down by...
75 turns.
Derive a neutral for grounding purposes.
A.C.
Inductance.

14. AC voltage is raised or lowered by means of...
5:1.
Check to make sure that the victim is not still in contact with the electricity.
Transformers.
At least two phases

15. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Inductance.
Tied together
100 turns.

16. 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?
At the source transformer.
3 -979 Volts.
They should be made by the same manufacturer.
Squirrel-cage rotor.

17. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
600 volts.
Continuous.
Derive a neutral for grounding purposes.
X.

18. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
25 feet.
Draw less current.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A.C.

19. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Reverse any two-phase leads.
X.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
277 volts.

20. 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?
100 turns.
12 to 15 times a minute.
A grounding resistor.
The chest should rise or inflate.

21. What is a capacitor?
An electromagnet.
A device used to store electrical energy.
Short-circuited after power has been removed.
12 to 15 times a minute.

22. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Circuit Breaker.
600 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.

23. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
An electromagnet.
Isolation transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
25 feet.

24. 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.
Current changing constantly in magnitude and periodically in direction.
60 Hertz
Lower current and higher voltage.

25. A control power transformer...
Current that changes constantly in magnitude and periodically in direction.
Larger than that found in the primary winding.
25 feet.
Provides single-phase power to smaller loads such as lights - heaters - etc.

26. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
Reverse its rotation.
100 volts.
Current changing constantly in magnitude and periodically in direction.

27. The size of a transformer is measured in...
25 feet.
Isolation transformer.
Kilovolt ampere (KVA).
Carotid pulse - which is located in the neck next to the Adam's apple.

28. The primary leads of a single-phase transformer should be connected to the...
H terminals.
Inductance.
Current changing constantly in magnitude and periodically in direction.
Lower current and higher voltage

29. 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
Kilovolt ampere (KVA).
7 -630 volts.
Isolation transformer.

30. 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.
Potential transformer.
The current will read zero.
Larger than that found in the primary winding.

31. A solenoid coil is...
Stator windings.
60 Hertz
Transformer
An electromagnet.

32. 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?
Transformer
75 turns.
Reverse its rotation.
No.6 AWG.

33. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage induction motor.
Reverse any two-phase leads.
Squirrel-cage rotor.
60 cycles per second (60 Hertz).

34. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Full-load - three-phase voltage.
Squirrel-cage induction motor.
Current that changes constantly in magnitude and periodically in direction.
Zero amps.

35. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
The sum of the two capacitors.
Reverse its rotation.
100 turns.

36. To protect against over-current in a three-phase circuit over-current protection must be provided for...
600 volts.
Two speeds
Alternating current.
At least two phases

37. If any two-phase wires are reversed on a three-phase motor - the motor will...
Lower current and higher voltage.
Capacitance.
Reverse its rotation.
Hyperventilation.

38. Not an acceptable method for the installations of surface transformers?
480 volts.
They must be installed at least 7 feet above the ground.
100 volts.
The chest should rise or inflate.

39. 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.
No.6 AWG.
Disconnect the frame-grounding conductor.
600 volts.

40. A burn causing a blister is classified as a...
Second-degree burn.
At the source transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
Stator windings.

41. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Larger than that found in the primary winding.
Current changing constantly in magnitude and periodically in direction.
The current will read zero.

42. At what rate should mouth-to-mouth resuscitation be applied?
At the source transformer.
12 to 15 times a minute.
A grounding resistor.
480 volts.

43. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Continuous.
Draw less current.
The chest should rise or inflate.

44. Current that changes periodically in direction is...
Two speeds
Alternating current.
480 volts.
At the source transformer.

45. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
60 Hertz
The capacitors should be discharged.
The chest should rise or inflate.
It provides good speed control.

46. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Current that changes constantly in magnitude and periodically in direction.
At the source transformer.
Short-circuited after power has been removed.
Isolation transformer.

47. The purpose of a zig-zag transformer is to...
The capacitors should be discharged.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Derive a neutral for grounding purposes.
They should be made by the same manufacturer.

48. Compared to the secondary of a loaded - step-down transformer - the primary has...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Second-degree burn.
A grounding resistor.
Lower current and higher voltage

49. The property of an electrical circuit that opposes any change in voltage is called...
Draw less current.
Reverse its rotation.
Capacitance.
Transformer

50. 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...
600 volts.
Full-load - three-phase voltage.
Draw less current.
200 volts AC.