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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. 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.
3 -979 Volts.
277 volts.
100 turns.

2. Where should grounding resistors be located?
Provides single-phase power to smaller loads such as lights - heaters - etc.
800 volts.
At the source transformer.
Larger than that found in the primary winding.

3. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Full-load - three-phase voltage.
Draw less current.
Capacitance.

4. A wound-rotor induction motor has all the following EXCEPT...
2000 watts
Current that changes constantly in magnitude and periodically in direction.
Squirrel-cage rotor.
It provides good speed control.

5. Not an acceptable method for the installations of surface transformers?
3 -979 Volts.
277 volts.
Derive a neutral for grounding purposes.
They must be installed at least 7 feet above the ground.

6. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Inductance.
No.6 AWG.
Transformer
150 turns.

7. 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.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Lower current and higher voltage
Transformer

8. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
100 volts.
277 volts.
800 volts.
A grounding resistor.

9. A control power transformer...
Cut around clothing that has adhered to the burned area.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Squirrel-cage rotor.
150 turns.

10. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
The motor rotation is reversed.
15 feet off the ground.
Second-degree burn.

11. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Draw less current.
1 amp.
25 feet.
Stator windings.

12. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
The chest should rise or inflate.
No.6 AWG.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
15 feet off the ground.

13. Not true about AC power?
100 turns.
60 Hertz
It provides good speed control.
12 to 15 times a minute.

14. The speed of an alternating current - squirrel-cage induction motor is...
Draw less current.
Nearly constant.
Short-circuited after power has been removed.
Draw less current.

15. The transformer used only to measure voltage is a...
1 amp.
H terminals.
Inductance.
Potential transformer.

16. Compared to the secondary of a loaded - step-down transformer - the primary has...
An electromagnet.
Lower current and higher voltage
3 -979 Volts.
Alternating current.

17. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
Four times less than that of the secondary.
Disconnect the frame-grounding conductor.
Full-load - three-phase voltage.

18. Current that changes periodically in direction is...
Alternating current.
Carotid pulse - which is located in the neck next to the Adam's apple.
The capacitors should be discharged.
100 volts.

19. The property of an electric circuit that opposes any change in current is called...
Reverse its rotation.
600 volts.
Inductance.
Allow for metering voltage and Current.

20. The property of an electrical circuit that opposes any change in voltage is called...
An electromagnet.
5:1.
Capacitance.
75 turns.

21. Which of the following does a squirrel cage induction motor have?
3 -979 Volts.
Transformers.
Stator windings.
Inductance.

22. What is the danger when working around capacitors?
Check to make sure that the victim is not still in contact with the electricity.
Tied together
The capacitors should be discharged.
An electrical shock hazard may exist.

23. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Grounded phase and ground fault devices were not operating.
Isolation transformer.
Disconnect the frame-grounding conductor.

24. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Transformers.
Draw less current.
75 turns.

25. What should the duty rating of a grounding resistor be?
Transformer
600 volts.
Continuous.
Reverse any two-phase leads.

26. 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.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Isolation transformer.
Squirrel-cage rotor.

27. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
Clamp-on ammeter.
5:1
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

28. All transformers step voltage up or down by...
Inductance.
Allow for metering voltage and Current.
Reverse its rotation.
Lower current and higher voltage.

29. The primary leads of a single-phase transformer should be connected to the...
Larger than that found in the primary winding.
Transformer
Check to make sure that the victim is not still in contact with the electricity.
H terminals.

30. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Continuous.
Draw less current.
The capacitors should be discharged.

31. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
800 volts.
The capacitors should be discharged.
Inductance.
Carotid pulse - which is located in the neck next to the Adam's apple.

32. 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?
They must be installed at least 7 feet above the ground.
60 cycles per second (60 Hertz).
600 volts.
The current will read zero.

33. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Two speeds
It provides good speed control.
Carotid pulse - which is located in the neck next to the Adam's apple.

34. If any two-phase wires are reversed on a three-phase motor - the motor will...
Disconnect the frame-grounding conductor.
480 volts.
Reverse its rotation.
75 turns.

35. Alternating current may be defined as...
Because less current flowing at high voltage causes less line loss per kilowatt.
Current that changes constantly in magnitude and periodically in direction.
The chest should rise or inflate.
480 volts.

36. 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.
Alternating current.
15 feet off the ground.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

37. 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?
Provides single-phase power to smaller loads such as lights - heaters - etc.
3 -979 Volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
Stator windings.

38. What steps up or steps down AC voltage?
An electromagnet.
Because less current flowing at high voltage causes less line loss per kilowatt.
Transformer
Current that changes constantly in magnitude and periodically in direction.

39. Current transformers - or CT's - are used to...
800 volts.
Larger than that found in the primary winding.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
25 feet.

40. The size of a transformer is measured in...
600 volts.
100 volts.
Kilovolt ampere (KVA).
The current will read zero.

41. How should clothing be removed from a burn?
Stator windings.
Because less current flowing at high voltage causes less line loss per kilowatt.
A.C.
Cut around clothing that has adhered to the burned area.

42. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
A device used to store electrical energy.
Electro-magnetism for their operation.
600 volts.

43. At what rate should mouth-to-mouth resuscitation be applied?
The chest should rise or inflate.
The sum of the two capacitors.
12 to 15 times a minute.
600 volts.

44. The primary function of a power transformer is to provide...
Continuous.
Short-circuited after power has been removed.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Full-load - three-phase voltage.

45. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
Larger than that found in the primary winding.
Full-load - three-phase voltage.
Short-circuited after power has been removed.

46. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Short-circuited after power has been removed.
Transformer
They must be installed at least 7 feet above the ground.

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

48. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
The capacitors should be discharged.
Continuous.
Current changing constantly in magnitude and periodically in direction.

49. What type motor is a wound-rotor induction motor?
Short-circuited after power has been removed.
800 volts.
A.C.
They must be installed at least 7 feet above the ground.

50. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
The sum of the two capacitors.
A step-up transformer.
It provides good speed control.
At least two phases