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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. 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...
Two speeds
100 volts.
A grounding resistor.
The current will read zero.

2. What type motor is a wound-rotor induction motor?
The capacitors should be discharged.
Hyperventilation.
A.C.
277 volts.

3. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
150 turns.
A device used to store electrical energy.
The motor rotation is reversed.

4. The secondary windings on a 10:1 step-down transformer will have a wire size...
Disconnect the frame-grounding conductor.
Larger than that found in the primary winding.
60 cycles per second (60 Hertz).
277 volts.

5. The property of an electric circuit that opposes any change in current is called...
Continuous.
Four times less than that of the secondary.
Lower current and higher voltage.
Inductance.

6. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Capacitance.
Inductance.
X.
15 feet off the ground.

7. High voltage is used to transmit power over long distances...
480 volts.
Nearly constant.
1 amp.
Because less current flowing at high voltage causes less line loss per kilowatt.

8. What type of 3-phase AC motor is used most often around a mine?
Alternating current.
A step-up transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
Squirrel-cage induction motor.

9. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
A grounding resistor.
7 -630 volts.
600 volts.
Nearly constant.

10. 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.
No.6 AWG.
5:1.
X.
Transformers.

11. 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...
5:1
Draw less current.
Electro-magnetism for their operation.
The current will read zero.

12. Define alternating current...
The capacitors should be discharged.
At the source transformer.
Current changing constantly in magnitude and periodically in direction.
Derive a neutral for grounding purposes.

13. At what rate should mouth-to-mouth resuscitation be applied?
Lower current and higher voltage
12 to 15 times a minute.
Short-circuited after power has been removed.
A device used to store electrical energy.

14. Where should grounding resistors be located?
Check to make sure that the victim is not still in contact with the electricity.
At the source transformer.
800 volts.
Cut around clothing that has adhered to the burned area.

15. When not connected to a load - the secondary leads of a current transformer should be...
Two speeds
Shunted and taped
150 turns.
Transformers.

16. The standard frequency of alternating current used at a mine is...
60 Hertz
Two speeds
Larger than that found in the primary winding.
75 turns.

17. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Kilovolt ampere (KVA).
Draw less current.
25 feet.
Full-load - three-phase voltage.

18. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
60 Hertz
Capacitance.
Draw less current.
480 volts.

19. What is the first step to be followed in aiding a victim of electrical shock?
5:1.
The capacitors should be discharged.
Check to make sure that the victim is not still in contact with the electricity.
Hyperventilation.

20. A solenoid coil is...
The sum of the two capacitors.
An electromagnet.
Disconnect the frame-grounding conductor.
Draw less current.

21. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Transformer
100 turns.
Check to make sure that the victim is not still in contact with the electricity.

22. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
75 turns.
Grounded phase and ground fault devices were not operating.
The chest should rise or inflate.
Circuit Breaker.

23. Operating coils - motors - transformers - relays and solenoids depend upon...
Transformers.
Electro-magnetism for their operation.
At the source transformer.
Shunted and taped

24. The transformer used only to measure voltage is a...
25 feet.
Current that changes constantly in magnitude and periodically in direction.
Potential transformer.
Larger than that found in the primary winding.

25. The property of an electrical circuit that opposes any change in voltage is called...
Carotid pulse - which is located in the neck next to the Adam's apple.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Isolation transformer.
Capacitance.

26. The speed of an alternating current - squirrel-cage induction motor is...
An electromagnet.
Shunted and taped
Nearly constant.
Capacitance.

27. 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?
480 volts.
15 feet off the ground.
The chest should rise or inflate.
3 -979 Volts.

28. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
800 volts.
An electromagnet.
Four times less than that of the secondary.

29. Not a symptom of electrical shock?.
Reverse any two-phase leads.
Hyperventilation.
Squirrel-cage induction motor.
At the source transformer.

30. 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?
Transformers.
They must be installed at least 7 feet above the ground.
600 volts.
Inductance.

31. Not true about AC power?
Squirrel-cage rotor.
Because less current flowing at high voltage causes less line loss per kilowatt.
It provides good speed control.
Provides single-phase power to smaller loads such as lights - heaters - etc.

32. 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?
Because less current flowing at high voltage causes less line loss per kilowatt.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
75 turns.
Check to make sure that the victim is not still in contact with the electricity.

33. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The current will read zero.
Reverse its rotation.
Continuous.
A device used to store electrical energy.

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

35. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
The current will read zero.
A grounding resistor.
The chest should rise or inflate.
X.

36. Compared to the secondary of a loaded - step-down transformer - the primary has...
7 -630 volts.
Allow for metering voltage and Current.
The chest should rise or inflate.
Lower current and higher voltage

37. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
The chest should rise or inflate.
They should be made by the same manufacturer.
Squirrel-cage induction motor.
Transformers.

38. Current that changes periodically in direction is...
Clamp-on ammeter.
Alternating current.
Carotid pulse - which is located in the neck next to the Adam's apple.
Check to make sure that the victim is not still in contact with the electricity.

39. All transformers step voltage up or down by...
A device used to store electrical energy.
12 to 15 times a minute.
Inductance.
Lower current and higher voltage.

40. A burn causing a blister is classified as a...
100 volts.
7 -630 volts.
The current will read zero.
Second-degree burn.

41. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
277 volts.
Grounded phase and ground fault devices were not operating.
60 Hertz
2000 watts

42. 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...
2000 watts
X.
Draw less current.
It provides good speed control.

43. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
75 turns.
Derive a neutral for grounding purposes.
150 turns.
Two speeds

44. The combined capacitance of two capacitors in parallel is...
75 turns.
5:1.
The motor rotation is reversed.
The sum of the two capacitors.

45. Not an acceptable method for the installations of surface transformers?
Alternating current.
They must be installed at least 7 feet above the ground.
75 turns.
Capacitance.

46. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
2000 watts
Full-load - three-phase voltage.
Four times less than that of the secondary.
5:1.

47. 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.
75 turns.
A device used to store electrical energy.
At least two phases

48. 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?
The capacitors should be discharged.
60 cycles per second (60 Hertz).
Squirrel-cage induction motor.
75 turns.

49. 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?
5:1
Circuit Breaker.
200 volts AC.
150 turns.

50. If any two-phase wires are reversed on a three-phase motor - the motor will...
Hyperventilation.
600 volts.
Reverse its rotation.
Disconnect the frame-grounding conductor.