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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. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
5:1
Inductance.
Continuous.

2. 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?
800 volts.
A grounding resistor.
277 volts.
They must be installed at least 7 feet above the ground.

3. The main function of CT's and PT's on a main substation is to...
2000 watts
Potential transformer.
Clamp-on ammeter.
Allow for metering voltage and Current.

4. A wound-rotor induction motor has all the following EXCEPT...
150 turns.
Squirrel-cage rotor.
At the source transformer.
277 volts.

5. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
800 volts.
A step-up transformer.
277 volts.
Nearly constant.

6. The primary leads of a single-phase transformer should be connected to the...
Provides single-phase power to smaller loads such as lights - heaters - etc.
2000 watts
Transformer
H terminals.

7. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
The capacitors should be discharged.
600 volts.
Cut around clothing that has adhered to the burned area.

8. High voltage is used to transmit power over long distances...
75 turns.
Because less current flowing at high voltage causes less line loss per kilowatt.
Current that changes constantly in magnitude and periodically in direction.
Full-load - three-phase voltage.

9. The standard frequency of power supplied by the power company is...
Nearly constant.
60 cycles per second (60 Hertz).
At least two phases
Electro-magnetism for their operation.

10. 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?
60 cycles per second (60 Hertz).
12 to 15 times a minute.
A grounding resistor.
75 turns.

11. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Electro-magnetism for their operation.
Squirrel-cage induction motor.
No.6 AWG.
7 -630 volts.

12. If any two-phase wires are reversed on a three-phase motor - the motor will...
480 volts.
Continuous.
A step-up transformer.
Reverse its rotation.

13. Current in an AC circuit may be measured by...
Clamp-on ammeter.
75 turns.
Electro-magnetism for their operation.
Inductance.

14. Compared to the secondary of a loaded - step-down transformer - the primary has...
Check to make sure that the victim is not still in contact with the electricity.
Kilovolt ampere (KVA).
Lower current and higher voltage.
Lower current and higher voltage

15. 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
Full-load - three-phase voltage.
Disconnect the frame-grounding conductor.
Transformers.

16. A transformer with a 1:1 ratio is usually a (an)...
X.
Current that changes constantly in magnitude and periodically in direction.
Isolation transformer.
Allow for metering voltage and Current.

17. AC voltage is raised or lowered by means of...
Continuous.
1 amp.
Transformers.
It provides good speed control.

18. At what rate should mouth-to-mouth resuscitation be applied?
Lower current and higher voltage
100 volts.
12 to 15 times a minute.
3 -979 Volts.

19. A control power transformer...
Allow for metering voltage and Current.
The motor rotation is reversed.
Provides single-phase power to smaller loads such as lights - heaters - etc.
X.

20. What type motor is a wound-rotor induction motor?
A.C.
Shunted and taped
An electromagnet.
Carotid pulse - which is located in the neck next to the Adam's apple.

21. To protect against over-current in a three-phase circuit over-current protection must be provided for...
They should be made by the same manufacturer.
They must be installed at least 7 feet above the ground.
Transformers.
At least two phases

22. A 3-phase - 2 speed - constant torque motor is running at fast speed. The motor windings are connected wye for fast speed. Motor leads T4 - T5 and T6 are connected to the line leads. Motor leads T1 - T2 and T3 should be...
Tied together
12 to 15 times a minute.
H terminals.
X.

23. What should the duty rating of a grounding resistor be?
480 volts.
Continuous.
Inductance.
The current will read zero.

24. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Continuous.
Shunted and taped
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
12 to 15 times a minute.

25. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
75 turns.
Disconnect the frame-grounding conductor.
Larger than that found in the primary winding.
The chest should rise or inflate.

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

27. Compared to the secondary of a loaded - step-down transformer - the primary has...
Kilovolt ampere (KVA).
Lower current and higher voltage
75 turns.
Squirrel-cage rotor.

28. 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.
Disconnect the frame-grounding conductor.
The capacitors should be discharged.
3 -979 Volts.

29. The standard frequency of alternating current used at a mine is...
12 to 15 times a minute.
7 -630 volts.
60 Hertz
15 feet off the ground.

30. Operating coils - motors - transformers - relays and solenoids depend upon...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Electro-magnetism for their operation.
Hyperventilation.
Two speeds

31. A solenoid coil is...
Second-degree burn.
An electromagnet.
Shunted and taped
Lower current and higher voltage

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?
Squirrel-cage induction motor.
Check to make sure that the victim is not still in contact with the electricity.
Reverse any two-phase leads.
75 turns.

33. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Potential transformer.
No.6 AWG.
Clamp-on ammeter.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

34. The transformer used only to measure voltage is a...
Zero amps.
Potential transformer.
Alternating current.
Carotid pulse - which is located in the neck next to the Adam's apple.

35. The speed of an alternating current - squirrel-cage induction motor is...
Hyperventilation.
Nearly constant.
480 volts.
277 volts.

36. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
3 -979 Volts.
H terminals.
The capacitors should be discharged.
Full-load - three-phase voltage.

37. How do you change the direction of a 3-phase AC motor?
5:1
Reverse any two-phase leads.
Stator windings.
2000 watts

38. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Two speeds
The current will read zero.
X.
Reverse any two-phase leads.

39. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Shunted and taped
Reverse any two-phase leads.
Squirrel-cage rotor.

40. Current that changes periodically in direction is...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Alternating current.
No.6 AWG.
The current will read zero.

41. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Inductance.
Short-circuited after power has been removed.
A.C.
Derive a neutral for grounding purposes.

42. What is a capacitor?
5:1.
A device used to store electrical energy.
600 volts.
Kilovolt ampere (KVA).

43. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
60 cycles per second (60 Hertz).
They should be made by the same manufacturer.
A step-up transformer.
A grounding resistor.

44. 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?
5:1.
3 -979 Volts.
Alternating current.
600 volts.

45. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Draw less current.
Current that changes constantly in magnitude and periodically in direction.
A grounding resistor.
At least two phases

46. The primary function of a power transformer is to provide...
A device used to store electrical energy.
Transformers.
15 feet off the ground.
Full-load - three-phase voltage.

47. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
150 turns.
Continuous.
Derive a neutral for grounding purposes.

48. All transformers step voltage up or down by...
Inductance.
60 Hertz
1 amp.
Current that changes constantly in magnitude and periodically in direction.

49. The property of an electrical circuit that opposes any change in voltage is called...
Allow for metering voltage and Current.
Grounded phase and ground fault devices were not operating.
Inductance.
Capacitance.

50. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Electro-magnetism for their operation.
Lower current and higher voltage
A step-up transformer.
75 turns.