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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. Alternating current may be defined as...
Capacitance.
Potential transformer.
Current that changes constantly in magnitude and periodically in direction.
3 -979 Volts.

2. 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.
480 volts.
Full-load - three-phase voltage.
An electromagnet.

3. What is the first step to be followed in aiding a victim of electrical shock?
Circuit Breaker.
Reverse its rotation.
Check to make sure that the victim is not still in contact with the electricity.
Shunted and taped

4. 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.
Larger than that found in the primary winding.
The motor rotation is reversed.
Continuous.

5. How should clothing be removed from a burn?
They should be made by the same manufacturer.
Cut around clothing that has adhered to the burned area.
2000 watts
At least two phases

6. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
X.
Clamp-on ammeter.
800 volts.

7. When not connected to a load - the secondary leads of a current transformer should be...
Derive a neutral for grounding purposes.
Shunted and taped
Alternating current.
Continuous.

8. Compared to the secondary of a loaded - step-down transformer - the primary has...
100 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
Lower current and higher voltage.
A.C.

9. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Reverse its rotation.
Transformers.
Full-load - three-phase voltage.

10. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Current changing constantly in magnitude and periodically in direction.
H terminals.
They should be made by the same manufacturer.
Nearly constant.

11. 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?
100 turns.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Grounded phase and ground fault devices were not operating.
150 turns.

12. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Current changing constantly in magnitude and periodically in direction.
The sum of the two capacitors.
7 -630 volts.
75 turns.

13. What is the danger when working around capacitors?
Stator windings.
150 turns.
277 volts.
An electrical shock hazard may exist.

14. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Reverse any two-phase leads.
Zero amps.
No.6 AWG.
Squirrel-cage induction motor.

15. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Alternating current.
Squirrel-cage induction motor.
480 volts.
277 volts.

16. What steps up or steps down AC voltage?
Transformer
100 turns.
Nearly constant.
Provides single-phase power to smaller loads such as lights - heaters - etc.

17. What should the duty rating of a grounding resistor be?
Continuous.
100 turns.
At least two phases
Current that changes constantly in magnitude and periodically in direction.

18. The standard frequency of power supplied by the power company is...
Full-load - three-phase voltage.
60 cycles per second (60 Hertz).
100 turns.
Second-degree burn.

19. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Circuit Breaker.
The current will read zero.
A grounding resistor.
600 volts.

20. The primary function of a power transformer is to provide...
Lower current and higher voltage
Full-load - three-phase voltage.
Squirrel-cage induction motor.
5:1.

21. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Alternating current.
A device used to store electrical energy.
480 volts.
15 feet off the ground.

22. 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...
A step-up transformer.
Current that changes constantly in magnitude and periodically in direction.
An electrical shock hazard may exist.
100 volts.

23. The property of an electric circuit that opposes any change in current is called...
Stator windings.
Kilovolt ampere (KVA).
Inductance.
Continuous.

24. The secondary windings on a 10:1 step-down transformer will have a wire size...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Current that changes constantly in magnitude and periodically in direction.
Larger than that found in the primary winding.

25. What type of 3-phase AC motor is used most often around a mine?
Potential transformer.
Squirrel-cage induction motor.
2000 watts
Draw less current.

26. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Tied together
5:1
The chest should rise or inflate.
Stator windings.

27. Current transformers - or CT's - are used to...
Capacitance.
Reverse any two-phase leads.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Continuous.

28. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Tied together
A.C.

29. 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...
A device used to store electrical energy.
The motor rotation is reversed.
Lower current and higher voltage
Draw less current.

30. 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?
75 turns.
Zero amps.
Check to make sure that the victim is not still in contact with the electricity.
The chest should rise or inflate.

31. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Larger than that found in the primary winding.
X.
Shunted and taped
A.C.

32. A wound-rotor induction motor has all the following EXCEPT...
Shunted and taped
Tied together
Squirrel-cage rotor.
Current that changes constantly in magnitude and periodically in direction.

33. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Lower current and higher voltage
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
It provides good speed control.
1 amp.

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

35. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Squirrel-cage rotor.
Squirrel-cage induction motor.
480 volts.
800 volts.

36. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
It provides good speed control.
800 volts.
Isolation transformer.

37. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Alternating current.
Shunted and taped
2000 watts
75 turns.

38. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
60 Hertz
Isolation transformer.
Disconnect the frame-grounding conductor.

39. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Current changing constantly in magnitude and periodically in direction.
Lower current and higher voltage.
Draw less current.
Four times less than that of the secondary.

40. Three-phase AC underground cables must be provided with overcurrent protection using a...
Derive a neutral for grounding purposes.
Reverse any two-phase leads.
At the source transformer.
Circuit Breaker.

41. A burn causing a blister is classified as a...
At least two phases
Second-degree burn.
Reverse any two-phase leads.
Derive a neutral for grounding purposes.

42. The transformer used only to measure voltage is a...
Allow for metering voltage and Current.
Potential transformer.
Inductance.
Shunted and taped

43. A transformer with a 1:1 ratio is usually a (an)...
A step-up transformer.
Isolation transformer.
Inductance.
Current changing constantly in magnitude and periodically in direction.

44. 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...
Lower current and higher voltage
Draw less current.
Disconnect the frame-grounding conductor.
60 cycles per second (60 Hertz).

45. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Inductance.
Short-circuited after power has been removed.
Hyperventilation.

46. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Derive a neutral for grounding purposes.
The motor rotation is reversed.
Hyperventilation.
60 Hertz

47. 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
Check to make sure that the victim is not still in contact with the electricity.
Reverse its rotation.
150 turns.

48. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Reverse its rotation.
Alternating current.
Inductance.
The current will read zero.

49. Not true about AC power?
It provides good speed control.
600 volts.
150 turns.
Check to make sure that the victim is not still in contact with the electricity.

50. Which of the following does a squirrel cage induction motor have?
Squirrel-cage rotor.
Stator windings.
150 turns.
Draw less current.