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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 speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Current that changes constantly in magnitude and periodically in direction.
1 amp.
Second-degree burn.

2. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
15 feet off the ground.
A.C.
A grounding resistor.

3. The standard frequency of alternating current used at a mine is...
100 turns.
Circuit Breaker.
60 Hertz
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

4. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The sum of the two capacitors.
An electromagnet.
The motor rotation is reversed.
5:1.

5. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
150 turns.
No.6 AWG.
480 volts.
Inductance.

6. 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?
150 turns.
Grounded phase and ground fault devices were not operating.
480 volts.
5:1

7. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Two speeds
The chest should rise or inflate.
Derive a neutral for grounding purposes.
Grounded phase and ground fault devices were not operating.

8. The combined capacitance of two capacitors in parallel is...
No.6 AWG.
The sum of the two capacitors.
Electro-magnetism for their operation.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

9. What is the danger when working around capacitors?
Disconnect the frame-grounding conductor.
At the source transformer.
An electrical shock hazard may exist.
Short-circuited after power has been removed.

10. Current in an AC circuit may be measured by...
75 turns.
Kilovolt ampere (KVA).
Clamp-on ammeter.
H terminals.

11. The primary function of a power transformer is to provide...
Tied together
Isolation transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
Full-load - three-phase voltage.

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

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13. The property of an electric circuit that opposes any change in current is called...
The current will read zero.
Derive a neutral for grounding purposes.
Draw less current.
Inductance.

14. 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?
A grounding resistor.
A step-up transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.
800 volts.

15. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Reverse any two-phase leads.
480 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
X.

16. A solenoid coil is...
277 volts.
A.C.
An electromagnet.
Two speeds

17. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The capacitors should be discharged.
An electromagnet.
2000 watts

18. 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?
277 volts.
15 feet off the ground.
200 volts AC.
60 cycles per second (60 Hertz).

19. 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.
200 volts AC.
At the source transformer.
At least two phases

20. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
800 volts.
25 feet.
A.C.
Isolation transformer.

21. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Shunted and taped
At least two phases
15 feet off the ground.
Transformers.

22. Not a symptom of electrical shock?.
Current that changes constantly in magnitude and periodically in direction.
Hyperventilation.
An electromagnet.
The capacitors should be discharged.

23. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
25 feet.
15 feet off the ground.
Carotid pulse - which is located in the neck next to the Adam's apple.
Potential transformer.

24. 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.
A step-up transformer.
Potential transformer.
Full-load - three-phase voltage.

25. The transformer used only to measure voltage is a...
Transformers.
Potential transformer.
Draw less current.
An electromagnet.

26. 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
Four times less than that of the secondary.
600 volts.
Stator windings.

27. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
200 volts AC.
600 volts.
5:1.

28. Which of the following does a squirrel cage induction motor have?
Stator windings.
3 -979 Volts.
An electrical shock hazard may exist.
7 -630 volts.

29. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Squirrel-cage rotor.
At least two phases
Shunted and taped
480 volts.

30. What steps up or steps down AC voltage?
Transformer
Short-circuited after power has been removed.
Tied together
7 -630 volts.

31. If any two-phase wires are reversed on a three-phase motor - the motor will...
200 volts AC.
Squirrel-cage induction motor.
Lower current and higher voltage.
Reverse its rotation.

32. What is the first step to be followed in aiding a victim of electrical shock?
480 volts.
60 Hertz
Check to make sure that the victim is not still in contact with the electricity.
Inductance.

33. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Draw less current.
75 turns.
A step-up transformer.
The motor rotation is reversed.

34. The purpose of a zig-zag transformer is to...
Kilovolt ampere (KVA).
200 volts AC.
Hyperventilation.
Derive a neutral for grounding purposes.

35. 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.
Draw less current.
Second-degree burn.
Reverse its rotation.

36. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
A step-up transformer.
Disconnect the frame-grounding conductor.
Draw less current.
Larger than that found in the primary winding.

37. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Draw less current.
Short-circuited after power has been removed.
Full-load - three-phase voltage.
5:1.

38. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Lower current and higher voltage.
Zero amps.
7 -630 volts.

39. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Allow for metering voltage and Current.
Reverse any two-phase leads.
Capacitance.

40. Not true about AC power?
75 turns.
It provides good speed control.
Current that changes constantly in magnitude and periodically in direction.
Inductance.

41. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
100 volts.
At the source transformer.
Capacitance.
Four times less than that of the secondary.

42. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
Electro-magnetism for their operation.
The sum of the two capacitors.
A grounding resistor.

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.
2000 watts
A device used to store electrical energy.
75 turns.

44. Current that changes periodically in direction is...
An electrical shock hazard may exist.
Alternating current.
The capacitors should be discharged.
H terminals.

45. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Reverse its rotation.
1 amp.
Two speeds
75 turns.

46. 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?
Kilovolt ampere (KVA).
The capacitors should be discharged.
Derive a neutral for grounding purposes.
75 turns.

47. Define alternating current...
2000 watts
Nearly constant.
Current changing constantly in magnitude and periodically in direction.
Second-degree burn.

48. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
5:1
A grounding resistor.
It provides good speed control.
Nearly constant.

49. AC voltage is raised or lowered by means of...
277 volts.
Check to make sure that the victim is not still in contact with the electricity.
H terminals.
Transformers.

50. Where should grounding resistors be located?
At the source transformer.
The capacitors should be discharged.
A.C.
Continuous.