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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. The standard frequency of alternating current used at a mine is...
A grounding resistor.
H terminals.
60 Hertz
A step-up transformer.

2. What is a capacitor?
A device used to store electrical energy.
Current that changes constantly in magnitude and periodically in direction.
60 Hertz
Larger than that found in the primary winding.

3. The combined capacitance of two capacitors in parallel is...
The motor rotation is reversed.
The sum of the two capacitors.
Nearly constant.
Reverse its rotation.

4. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Cut around clothing that has adhered to the burned area.
Full-load - three-phase voltage.
Lower current and higher voltage.
277 volts.

5. Not a symptom of electrical shock?.
An electrical shock hazard may exist.
5:1.
Hyperventilation.
The sum of the two capacitors.

6. High voltage is used to transmit power over long distances...
Transformer
1 amp.
Because less current flowing at high voltage causes less line loss per kilowatt.
Draw less current.

7. Three-phase AC underground cables must be provided with overcurrent protection using a...
Grounded phase and ground fault devices were not operating.
A step-up transformer.
The capacitors should be discharged.
Circuit Breaker.

8. The standard frequency of power supplied by the power company is...
The chest should rise or inflate.
Short-circuited after power has been removed.
An electromagnet.
60 cycles per second (60 Hertz).

9. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Alternating current.
The sum of the two capacitors.
Disconnect the frame-grounding conductor.
Electro-magnetism for their operation.

10. What steps up or steps down AC voltage?
Transformer
Cut around clothing that has adhered to the burned area.
Full-load - three-phase voltage.
Shunted and taped

11. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Allow for metering voltage and Current.
25 feet.
75 turns.

12. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
An electromagnet.
15 feet off the ground.
Full-load - three-phase voltage.
Check to make sure that the victim is not still in contact with the electricity.

13. 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...
Lower current and higher voltage.
Disconnect the frame-grounding conductor.
Draw less current.
A device used to store electrical energy.

14. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Isolation transformer.
The capacitors should be discharged.
Draw less current.
Cut around clothing that has adhered to the burned area.

15. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Potential transformer.
2000 watts
No.6 AWG.
Draw less current.

16. The speed of an alternating current - squirrel-cage induction motor is...
Lower current and higher voltage.
The chest should rise or inflate.
75 turns.
Nearly constant.

17. Compared to the secondary of a loaded - step-down transformer - the primary has...
Continuous.
Squirrel-cage induction motor.
Kilovolt ampere (KVA).
Lower current and higher voltage

18. The transformer used only to measure voltage is a...
5:1.
They should be made by the same manufacturer.
Potential transformer.
200 volts AC.

19. Current that changes periodically in direction is...
Alternating current.
X.
100 volts.
The sum of the two capacitors.

20. How should clothing be removed from a burn?
150 turns.
3 -979 Volts.
Cut around clothing that has adhered to the burned area.
X.

21. 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?
1 amp.
600 volts.
Electro-magnetism for their operation.
Lower current and higher voltage.

22. Which of the following does a squirrel cage induction motor have?
Carotid pulse - which is located in the neck next to the Adam's apple.
7 -630 volts.
12 to 15 times a minute.
Stator windings.

23. 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.
Check to make sure that the victim is not still in contact with the electricity.
Inductance.
X.

24. 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.
5:1.
Clamp-on ammeter.
Hyperventilation.
100 turns.

25. 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?
Second-degree burn.
Cut around clothing that has adhered to the burned area.
Allow for metering voltage and Current.
800 volts.

26. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
100 volts.
An electromagnet.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Shunted and taped

27. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
1 amp.
Cut around clothing that has adhered to the burned area.
The motor rotation is reversed.

28. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Zero amps.
5:1.
Two speeds

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?
Inductance.
Clamp-on ammeter.
200 volts AC.
150 turns.

30. The primary function of a power transformer is to provide...
Derive a neutral for grounding purposes.
Disconnect the frame-grounding conductor.
Capacitance.
Full-load - three-phase voltage.

31. 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...
The current will read zero.
Current changing constantly in magnitude and periodically in direction.
Tied together
The chest should rise or inflate.

32. If any two-phase wires are reversed on a three-phase motor - the motor will...
It provides good speed control.
Hyperventilation.
60 Hertz
Reverse its rotation.

33. A control power transformer...
It provides good speed control.
Current changing constantly in magnitude and periodically in direction.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Tied together

34. Operating coils - motors - transformers - relays and solenoids depend upon...
A.C.
Electro-magnetism for their operation.
Two speeds
600 volts.

35. The property of an electric circuit that opposes any change in current is called...
X.
Inductance.
200 volts AC.
1 amp.

36. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Lower current and higher voltage
The motor rotation is reversed.
Short-circuited after power has been removed.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

37. To protect against over-current in a three-phase circuit over-current protection must be provided for...
15 feet off the ground.
No.6 AWG.
Squirrel-cage rotor.
At least two phases

38. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Circuit Breaker.
Zero amps.
The motor rotation is reversed.
Stator windings.

39. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
A device used to store electrical energy.
15 feet off the ground.
12 to 15 times a minute.

40. Not an acceptable method for the installations of surface transformers?
Allow for metering voltage and Current.
Continuous.
Zero amps.
They must be installed at least 7 feet above the ground.

41. The secondary windings on a 10:1 step-down transformer will have a wire size...
An electromagnet.
Inductance.
A device used to store electrical energy.
Larger than that found in the primary winding.

42. Define alternating current...
The capacitors should be discharged.
Current that changes constantly in magnitude and periodically in direction.
Current changing constantly in magnitude and periodically in direction.
Check to make sure that the victim is not still in contact with the electricity.

43. Where should grounding resistors be located?
Transformers.
Electro-magnetism for their operation.
Reverse its rotation.
At the source transformer.

44. 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...
1 amp.
100 volts.
Short-circuited after power has been removed.
H terminals.

45. The property of an electrical circuit that opposes any change in voltage is called...
75 turns.
Draw less current.
Capacitance.
An electrical shock hazard may exist.

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...
Lower current and higher voltage
Draw less current.
An electromagnet.
Shunted and taped

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

48. What should the duty rating of a grounding resistor be?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Electro-magnetism for their operation.
Continuous.
Squirrel-cage rotor.

49. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Potential transformer.
They must be installed at least 7 feet above the ground.
A.C.
X.

50. Current in an AC circuit may be measured by...
Inductance.
Electro-magnetism for their operation.
Clamp-on ammeter.
Because less current flowing at high voltage causes less line loss per kilowatt.