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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. Compared to the secondary of a loaded - step-down transformer - the primary has...
Zero amps.
Lower current and higher voltage
25 feet.
Transformer

2. 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...
Kilovolt ampere (KVA).
Draw less current.
Potential transformer.
5:1

3. A solenoid coil is...
Zero amps.
An electromagnet.
2000 watts
Reverse any two-phase leads.

4. 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.
5:1.
Inductance.
An electrical shock hazard may exist.

5. 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?
At least two phases
Provides single-phase power to smaller loads such as lights - heaters - etc.
800 volts.
Disconnect the frame-grounding conductor.

6. 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...
60 Hertz
Inductance.
Tied together
1 amp.

7. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
Alternating current.
Short-circuited after power has been removed.
They should be made by the same manufacturer.

8. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Transformers.
Electro-magnetism for their operation.
75 turns.

9. A burn causing a blister is classified as a...
Second-degree burn.
Potential transformer.
A grounding resistor.
The chest should rise or inflate.

10. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
The motor rotation is reversed.
Inductance.
The chest should rise or inflate.

11. Compared to the secondary of a loaded - step-down transformer - the primary has...
100 turns.
Lower current and higher voltage.
Inductance.
X.

12. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
A grounding resistor.
Current changing constantly in magnitude and periodically in direction.
100 turns.

13. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Shunted and taped
They must be installed at least 7 feet above the ground.
A grounding resistor.
Continuous.

14. 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.
Hyperventilation.
25 feet.
Check to make sure that the victim is not still in contact with the electricity.

15. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Disconnect the frame-grounding conductor.
Tied together
25 feet.
2000 watts

16. 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...
Draw less current.
Zero amps.
Cut around clothing that has adhered to the burned area.
Lower current and higher voltage

17. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
7 -630 volts.
The motor rotation is reversed.
Reverse any two-phase leads.
100 volts.

18. How should clothing be removed from a burn?
2000 watts
No.6 AWG.
Electro-magnetism for their operation.
Cut around clothing that has adhered to the burned area.

19. What should the duty rating of a grounding resistor be?
Potential transformer.
The chest should rise or inflate.
7 -630 volts.
Continuous.

20. High voltage is used to transmit power over long distances...
H terminals.
100 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
Derive a neutral for grounding purposes.

21. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
60 Hertz
Second-degree burn.
No.6 AWG.

22. A wound-rotor induction motor has all the following EXCEPT...
Lower current and higher voltage
At least two phases
A device used to store electrical energy.
Squirrel-cage rotor.

23. The primary leads of a single-phase transformer should be connected to the...
Because less current flowing at high voltage causes less line loss per kilowatt.
H terminals.
12 to 15 times a minute.
7 -630 volts.

24. All transformers step voltage up or down by...
60 cycles per second (60 Hertz).
75 turns.
Inductance.
Electro-magnetism for their operation.

25. The secondary windings on a 10:1 step-down transformer will have a wire size...
7 -630 volts.
60 Hertz
Larger than that found in the primary winding.
Draw less current.

26. The property of an electrical circuit that opposes any change in voltage is called...
1 amp.
Two speeds
Check to make sure that the victim is not still in contact with the electricity.
Capacitance.

27. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Inductance.
An electromagnet.
Draw less current.

28. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Second-degree burn.
The capacitors should be discharged.
Electro-magnetism for their operation.
Circuit Breaker.

29. 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?
Check to make sure that the victim is not still in contact with the electricity.
2000 watts
Potential transformer.
150 turns.

30. 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?
Inductance.
Allow for metering voltage and Current.
Zero amps.
75 turns.

31. Current that changes periodically in direction is...
Shunted and taped
Continuous.
Alternating current.
5:1

32. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Potential transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Draw less current.

33. The transformer used only to measure voltage is a...
2000 watts
They must be installed at least 7 feet above the ground.
The current will read zero.
Potential transformer.

34. Not true about AC power?
It provides good speed control.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
150 turns.
Cut around clothing that has adhered to the burned area.

35. 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?
Two speeds
Alternating current.
An electrical shock hazard may exist.
75 turns.

36. The speed of an alternating current - squirrel-cage induction motor is...
Check to make sure that the victim is not still in contact with the electricity.
Nearly constant.
15 feet off the ground.
No.6 AWG.

37. Not an acceptable method for the installations of surface transformers?
Potential transformer.
Continuous.
The current will read zero.
They must be installed at least 7 feet above the ground.

38. 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.
Reverse any two-phase leads.
A device used to store electrical energy.
Clamp-on ammeter.

39. The standard frequency of alternating current used at a mine is...
25 feet.
5:1.
The sum of the two capacitors.
60 Hertz

40. The property of an electric circuit that opposes any change in current is called...
X.
Zero amps.
Inductance.
60 Hertz

41. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
A.C.
Provides single-phase power to smaller loads such as lights - heaters - etc.
25 feet.
X.

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

43. 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?
600 volts.
Four times less than that of the secondary.
Reverse its rotation.
Second-degree burn.

44. Define alternating current...
They should be made by the same manufacturer.
Full-load - three-phase voltage.
Draw less current.
Current changing constantly in magnitude and periodically in direction.

45. A control power transformer...
It provides good speed control.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Current that changes constantly in magnitude and periodically in direction.
Potential transformer.

46. Where should grounding resistors be located?
A step-up transformer.
At the source transformer.
5:1.
60 Hertz

47. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
At least two phases
25 feet.
The chest should rise or inflate.
At the source transformer.

48. Alternating current may be defined as...
25 feet.
1 amp.
Current that changes constantly in magnitude and periodically in direction.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

49. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
15 feet off the ground.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Kilovolt ampere (KVA).

50. The purpose of a zig-zag transformer is to...
3 -979 Volts.
At the source transformer.
Reverse any two-phase leads.
Derive a neutral for grounding purposes.