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. 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?
An electrical shock hazard may exist.
The chest should rise or inflate.
An electromagnet.
150 turns.

2. 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.
The sum of the two capacitors.
100 turns.
75 turns.
5:1

3. Current in an AC circuit may be measured by...
Two speeds
Second-degree burn.
Tied together
Clamp-on ammeter.

4. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Current that changes constantly in magnitude and periodically in direction.
Disconnect the frame-grounding conductor.
Short-circuited after power has been removed.
No.6 AWG.

5. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
600 volts.
A step-up transformer.
Short-circuited after power has been removed.
Allow for metering voltage and Current.

6. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
An electromagnet.
Draw less current.
Tied together

7. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
Capacitance.
600 volts.
At the source transformer.

8. The size of a transformer is measured in...
Check to make sure that the victim is not still in contact with the electricity.
Kilovolt ampere (KVA).
Allow for metering voltage and Current.
Squirrel-cage rotor.

9. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
100 volts.
Nearly constant.
800 volts.
The capacitors should be discharged.

10. A burn causing a blister is classified as a...
Second-degree burn.
They should be made by the same manufacturer.
Shunted and taped
X.

11. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
X.
Because less current flowing at high voltage causes less line loss per kilowatt.
A grounding resistor.
Potential transformer.

12. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
An electromagnet.
Isolation transformer.
Grounded phase and ground fault devices were not operating.
Four times less than that of the secondary.

13. Not a symptom of electrical shock?.
Hyperventilation.
H terminals.
Isolation transformer.
Larger than that found in the primary winding.

14. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
They must be installed at least 7 feet above the ground.
A.C.
A grounding resistor.

15. Which of the following does a squirrel cage induction motor have?
Stator windings.
No.6 AWG.
100 volts.
Kilovolt ampere (KVA).

16. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
600 volts.
Larger than that found in the primary winding.
7 -630 volts.
Four times less than that of the secondary.

17. What is the danger when working around capacitors?
Transformer
An electrical shock hazard may exist.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The sum of the two capacitors.

18. 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?
Alternating current.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Electro-magnetism for their operation.
600 volts.

19. Operating coils - motors - transformers - relays and solenoids depend upon...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Electro-magnetism for their operation.
75 turns.
480 volts.

20. What is a capacitor?
277 volts.
Continuous.
Circuit Breaker.
A device used to store electrical energy.

21. A wound-rotor induction motor has all the following EXCEPT...
Reverse any two-phase leads.
Squirrel-cage rotor.
800 volts.
Short-circuited after power has been removed.

22. All transformers step voltage up or down by...
Inductance.
800 volts.
The current will read zero.
An electrical shock hazard may exist.

23. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
A grounding resistor.
No.6 AWG.
Short-circuited after power has been removed.
Continuous.

24. AC voltage is raised or lowered by means of...
Carotid pulse - which is located in the neck next to the Adam's apple.
X.
Transformers.
Hyperventilation.

25. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Draw less current.
100 turns.
800 volts.
25 feet.

26. Current transformers - or CT's - are used to...
Derive a neutral for grounding purposes.
An electrical shock hazard may exist.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Because less current flowing at high voltage causes less line loss per kilowatt.

27. 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
15 feet off the ground.
Current changing constantly in magnitude and periodically in direction.
A device used to store electrical energy.

28. The property of an electrical circuit that opposes any change in voltage is called...
At the source transformer.
Capacitance.
Four times less than that of the secondary.
75 turns.

29. How do you change the direction of a 3-phase AC motor?
Isolation transformer.
Reverse any two-phase leads.
Reverse its rotation.
Clamp-on ammeter.

30. 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.
Short-circuited after power has been removed.
Four times less than that of the secondary.
200 volts AC.

31. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
15 feet off the ground.
Zero amps.
The chest should rise or inflate.
600 volts.

32. Compared to the secondary of a loaded - step-down transformer - the primary has...
600 volts.
Short-circuited after power has been removed.
Because less current flowing at high voltage causes less line loss per kilowatt.
Lower current and higher voltage.

33. Not an acceptable method for the installations of surface transformers?
Capacitance.
Current that changes constantly in magnitude and periodically in direction.
They must be installed at least 7 feet above the ground.
Second-degree burn.

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

35. Current that changes periodically in direction is...
They should be made by the same manufacturer.
Electro-magnetism for their operation.
Alternating current.
Zero amps.

36. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Grounded phase and ground fault devices were not operating.
Current changing constantly in magnitude and periodically in direction.
60 Hertz

37. 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.
Disconnect the frame-grounding conductor.
600 volts.
The motor rotation is reversed.

38. What should the duty rating of a grounding resistor be?
Tied together
Larger than that found in the primary winding.
Continuous.
Squirrel-cage rotor.

39. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Two speeds
480 volts.
Hyperventilation.
Alternating current.

40. Not true about AC power?
No.6 AWG.
12 to 15 times a minute.
Draw less current.
It provides good speed control.

41. The primary function of a power transformer is to provide...
12 to 15 times a minute.
They should be made by the same manufacturer.
3 -979 Volts.
Full-load - three-phase voltage.

42. The property of an electric circuit that opposes any change in current is called...
Tied together
Draw less current.
100 volts.
Inductance.

43. The main function of CT's and PT's on a main substation is to...
200 volts AC.
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.
Allow for metering voltage and Current.

44. The standard frequency of alternating current used at a mine is...
Four times less than that of the secondary.
60 Hertz
Current changing constantly in magnitude and periodically in direction.
Isolation transformer.

45. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
12 to 15 times a minute.
H terminals.
5:1.

46. If any two-phase wires are reversed on a three-phase motor - the motor will...
Allow for metering voltage and Current.
Carotid pulse - which is located in the neck next to the Adam's apple.
Reverse its rotation.
Zero amps.

47. Alternating current may be defined as...
Check to make sure that the victim is not still in contact with the electricity.
Lower current and higher voltage.
Two speeds
Current that changes constantly in magnitude and periodically in direction.

48. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
Clamp-on ammeter.
Larger than that found in the primary winding.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

49. At what rate should mouth-to-mouth resuscitation be applied?
Clamp-on ammeter.
12 to 15 times a minute.
A device used to store electrical energy.
Lower current and higher voltage

50. 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...
Draw less current.
Check to make sure that the victim is not still in contact with the electricity.
The chest should rise or inflate.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.