Test your basic knowledge |

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...
Hyperventilation.
Lower current and higher voltage.
Second-degree burn.
60 Hertz

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.
12 to 15 times a minute.
Provides single-phase power to smaller loads such as lights - heaters - etc.
100 turns.

3. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Alternating current.
Isolation transformer.
100 volts.

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

5. If any two-phase wires are reversed on a three-phase motor - the motor will...
The motor rotation is reversed.
Reverse its rotation.
The current will read zero.
They should be made by the same manufacturer.

6. Which of the following does a squirrel cage induction motor have?
60 Hertz
H terminals.
Four times less than that of the secondary.
Stator windings.

7. High voltage is used to transmit power over long distances...
480 volts.
5:1
The capacitors should be discharged.
Because less current flowing at high voltage causes less line loss per kilowatt.

8. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
At least two phases
The chest should rise or inflate.
Squirrel-cage induction motor.
They should be made by the same manufacturer.

9. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Second-degree burn.
7 -630 volts.
Transformer
X.

10. A transformer with a 1:1 ratio is usually a (an)...
2000 watts
Isolation transformer.
X.
480 volts.

11. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Cut around clothing that has adhered to the burned area.
800 volts.
No.6 AWG.
Circuit Breaker.

12. What is a capacitor?
Capacitance.
Isolation transformer.
A device used to store electrical energy.
Current that changes constantly in magnitude and periodically in direction.

13. The standard frequency of alternating current used at a mine is...
800 volts.
60 Hertz
200 volts AC.
The sum of the two capacitors.

14. A burn causing a blister is classified as a...
Second-degree burn.
1 amp.
The sum of the two capacitors.
A grounding resistor.

15. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
25 feet.
The sum of the two capacitors.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Short-circuited after power has been removed.

16. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
3 -979 Volts.
Reverse its rotation.
Four times less than that of the secondary.
Capacitance.

17. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Potential transformer.
600 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
Zero amps.

18. Not true about AC power?
A grounding resistor.
At the source transformer.
It provides good speed control.
A step-up transformer.

19. Current that changes periodically in direction is...
Circuit Breaker.
Alternating current.
Allow for metering voltage and Current.
Electro-magnetism for their operation.

20. 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?
Short-circuited after power has been removed.
Because less current flowing at high voltage causes less line loss per kilowatt.
75 turns.
Derive a neutral for grounding purposes.

21. 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?
800 volts.
Allow for metering voltage and Current.
Capacitance.
150 turns.

22. A wound-rotor induction motor has all the following EXCEPT...
Carotid pulse - which is located in the neck next to the Adam's apple.
Squirrel-cage rotor.
75 turns.
Provides single-phase power to smaller loads such as lights - heaters - etc.

23. To protect against over-current in a three-phase circuit over-current protection must be provided for...
75 turns.
Reverse any two-phase leads.
At least two phases
X.

24. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Cut around clothing that has adhered to the burned area.
Inductance.
The capacitors should be discharged.
Disconnect the frame-grounding conductor.

25. 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.
Circuit Breaker.
Check to make sure that the victim is not still in contact with the electricity.
5:1.
277 volts.

26. Three-phase AC underground cables must be provided with overcurrent protection using a...
Transformer
Circuit Breaker.
Lower current and higher voltage.
Larger than that found in the primary winding.

27. Not an acceptable method for the installations of surface transformers?
100 volts.
They must be installed at least 7 feet above the ground.
Full-load - three-phase voltage.
7 -630 volts.

28. All transformers step voltage up or down by...
They should be made by the same manufacturer.
Full-load - three-phase voltage.
Inductance.
480 volts.

29. The combined capacitance of two capacitors in parallel is...
Because less current flowing at high voltage causes less line loss per kilowatt.
60 cycles per second (60 Hertz).
Draw less current.
The sum of the two capacitors.

30. 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?
Current that changes constantly in magnitude and periodically in direction.
Circuit Breaker.
They must be installed at least 7 feet above the ground.
600 volts.

31. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Tied together
15 feet off the ground.
Two speeds
Hyperventilation.

32. Operating coils - motors - transformers - relays and solenoids depend upon...
The sum of the two capacitors.
Electro-magnetism for their operation.
Squirrel-cage rotor.
Clamp-on ammeter.

33. The primary leads of a single-phase transformer should be connected to the...
200 volts AC.
Cut around clothing that has adhered to the burned area.
H terminals.
Zero amps.

34. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Potential transformer.
They must be installed at least 7 feet above the ground.
A device used to store electrical energy.

35. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
75 turns.
They must be installed at least 7 feet above the ground.
Clamp-on ammeter.

36. Current transformers - or CT's - are used to...
Nearly constant.
The current will read zero.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
60 cycles per second (60 Hertz).

37. 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...
They should be made by the same manufacturer.
H terminals.
100 volts.
2000 watts

38. What is the danger when working around capacitors?
An electrical shock hazard may exist.
It provides good speed control.
12 to 15 times a minute.
Current that changes constantly in magnitude and periodically in direction.

39. 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?
Squirrel-cage induction motor.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
75 turns.
Four times less than that of the secondary.

40. 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 grounding resistor.
Draw less current.
Allow for metering voltage and Current.
Transformer

41. 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
600 volts.
200 volts AC.
Potential transformer.

42. Find the turns ratio of a single-phase transformer with the following values: Primary power of 5KW - secondary current of 100 amps - and primary voltage of 250 volts.
Stator windings.
7 -630 volts.
At the source transformer.
5:1

43. The size of a transformer is measured in...
At least two phases
Reverse any two-phase leads.
150 turns.
Kilovolt ampere (KVA).

44. Where should grounding resistors be located?
At the source transformer.
Inductance.
1 amp.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

45. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
25 feet.
Derive a neutral for grounding purposes.
Current that changes constantly in magnitude and periodically in direction.

46. The purpose of a zig-zag transformer is to...
100 turns.
Derive a neutral for grounding purposes.
Squirrel-cage rotor.
A device used to store electrical energy.

47. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Isolation transformer.
2000 watts
The motor rotation is reversed.
A grounding resistor.

48. AC voltage is raised or lowered by means of...
Transformers.
The chest should rise or inflate.
100 turns.
277 volts.

49. What type of 3-phase AC motor is used most often around a mine?
An electrical shock hazard may exist.
15 feet off the ground.
Hyperventilation.
Squirrel-cage induction motor.

50. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
At the source transformer.
Shunted and taped
Provides single-phase power to smaller loads such as lights - heaters - etc.
X.

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AC Theory

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After Effects Keyboard Shortcuts

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