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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. What should the duty rating of a grounding resistor be?
Reverse any two-phase leads.
Continuous.
Shunted and taped
Current that changes constantly in magnitude and periodically in direction.

2. What is the danger when working around capacitors?
1 amp.
Second-degree burn.
An electrical shock hazard may exist.
Squirrel-cage induction motor.

3. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
Capacitance.
150 turns.
Potential transformer.

4. 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?
60 cycles per second (60 Hertz).
H terminals.
75 turns.
600 volts.

5. The property of an electrical circuit that opposes any change in voltage is called...
Squirrel-cage rotor.
Capacitance.
Nearly constant.
The motor rotation is reversed.

6. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Electro-magnetism for their operation.
It provides good speed control.
A grounding resistor.
1 amp.

7. The size of a transformer is measured in...
Kilovolt ampere (KVA).
600 volts.
A grounding resistor.
12 to 15 times a minute.

8. 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...
Disconnect the frame-grounding conductor.
Tied together
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Check to make sure that the victim is not still in contact with the electricity.

9. Not true about AC power?
It provides good speed control.
A step-up transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.
3 -979 Volts.

10. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Lower current and higher voltage
Transformers.
They should be made by the same manufacturer.

11. How should clothing be removed from a burn?
Larger than that found in the primary winding.
Transformer
Check to make sure that the victim is not still in contact with the electricity.
Cut around clothing that has adhered to the burned area.

12. The secondary windings on a 10:1 step-down transformer will have a wire size...
100 volts.
Allow for metering voltage and Current.
Larger than that found in the primary winding.
X.

13. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
A grounding resistor.
No.6 AWG.
Draw less current.
Disconnect the frame-grounding conductor.

14. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Reverse its rotation.
Four times less than that of the secondary.
An electrical shock hazard may exist.
Draw less current.

15. The purpose of a zig-zag transformer is to...
Because less current flowing at high voltage causes less line loss per kilowatt.
Derive a neutral for grounding purposes.
Squirrel-cage rotor.
The motor rotation is reversed.

16. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
At least two phases
The sum of the two capacitors.
No.6 AWG.
They must be installed at least 7 feet above the ground.

17. 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?
Capacitance.
75 turns.
60 Hertz
A.C.

18. The property of an electric circuit that opposes any change in current is called...
They should be made by the same manufacturer.
Inductance.
They must be installed at least 7 feet above the ground.
Nearly constant.

19. Define alternating current...
Squirrel-cage rotor.
Current changing constantly in magnitude and periodically in direction.
Check to make sure that the victim is not still in contact with the electricity.
An electrical shock hazard may exist.

20. What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
It provides good speed control.
Electro-magnetism for their operation.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

21. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
No.6 AWG.
Alternating current.
Continuous.

22. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Second-degree burn.
Tied together
Short-circuited after power has been removed.
25 feet.

23. A burn causing a blister is classified as a...
60 cycles per second (60 Hertz).
Second-degree burn.
H terminals.
Allow for metering voltage and Current.

24. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
277 volts.
15 feet off the ground.
It provides good speed control.
Draw less current.

25. The primary function of a power transformer is to provide...
Allow for metering voltage and Current.
200 volts AC.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Full-load - three-phase voltage.

26. Where should grounding resistors be located?
Continuous.
At the source transformer.
Alternating current.
Reverse any two-phase leads.

27. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Two speeds
Hyperventilation.
1 amp.
Grounded phase and ground fault devices were not operating.

28. All transformers step voltage up or down by...
Inductance.
Continuous.
An electromagnet.
Two speeds

29. The standard frequency of power supplied by the power company is...
Shunted and taped
Stator windings.
60 cycles per second (60 Hertz).
Alternating current.

30. 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...
600 volts.
100 volts.
Shunted and taped
They should be made by the same manufacturer.

31. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Reverse its rotation.
Clamp-on ammeter.

32. What position of a selector switch using a voltmeter would you select to check a 120-volt AC circuit to obtain the most accurate reading?
200 volts AC.
Lower current and higher voltage
Alternating current.
Continuous.

33. A wound-rotor induction motor has all the following EXCEPT...
150 turns.
A step-up transformer.
Squirrel-cage rotor.
An electrical shock hazard may exist.

34. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
The motor rotation is reversed.
Shunted and taped
Zero amps.
277 volts.

35. The primary leads of a single-phase transformer should be connected to the...
Electro-magnetism for their operation.
Circuit Breaker.
At least two phases
H terminals.

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.
Inductance.
No.6 AWG.
3 -979 Volts.

37. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Capacitance.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
100 turns.

38. What steps up or steps down AC voltage?
Transformer
At the source transformer.
Current that changes constantly in magnitude and periodically in direction.
The current will read zero.

39. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
Grounded phase and ground fault devices were not operating.
200 volts AC.
At the source transformer.

40. The main function of CT's and PT's on a main substation is to...
Lower current and higher voltage.
Continuous.
Allow for metering voltage and Current.
15 feet off the ground.

41. At what rate should mouth-to-mouth resuscitation be applied?
75 turns.
It provides good speed control.
Current changing constantly in magnitude and periodically in direction.
12 to 15 times a minute.

42. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Stator windings.
The current will read zero.
Current changing constantly in magnitude and periodically in direction.
12 to 15 times a minute.

43. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
75 turns.
Disconnect the frame-grounding conductor.
The motor rotation is reversed.
At least two phases

44. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Short-circuited after power has been removed.
A step-up transformer.
It provides good speed control.
Allow for metering voltage and Current.

45. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
3 -979 Volts.
Derive a neutral for grounding purposes.
Lower current and higher voltage.

46. 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...
Two speeds
Draw less current.
They must be installed at least 7 feet above the ground.
The chest should rise or inflate.

47. Current that changes periodically in direction is...
Potential transformer.
Cut around clothing that has adhered to the burned area.
Alternating current.
60 Hertz

48. Compared to the secondary of a loaded - step-down transformer - the primary has...
Inductance.
Lower current and higher voltage
Capacitance.
Squirrel-cage rotor.

49. If any two-phase wires are reversed on a three-phase motor - the motor will...
Because less current flowing at high voltage causes less line loss per kilowatt.
X.
480 volts.
Reverse its rotation.

50. 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?
Reverse its rotation.
Electro-magnetism for their operation.
Potential transformer.
600 volts.