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

2. The standard frequency of power supplied by the power company is...
Transformer
60 cycles per second (60 Hertz).
60 Hertz
Inductance.

3. 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
Current changing constantly in magnitude and periodically in direction.
No.6 AWG.
25 feet.

4. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
The chest should rise or inflate.
15 feet off the ground.
Full-load - three-phase voltage.

5. When not connected to a load - the secondary leads of a current transformer should be...
Zero amps.
Shunted and taped
15 feet off the ground.
Nearly constant.

6. What is a capacitor?
A device used to store electrical energy.
Clamp-on ammeter.
Reverse its rotation.
Carotid pulse - which is located in the neck next to the Adam's apple.

7. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Kilovolt ampere (KVA).
Disconnect the frame-grounding conductor.
Electro-magnetism for their operation.
They should be made by the same manufacturer.

8. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
75 turns.
7 -630 volts.
600 volts.
The sum of the two capacitors.

9. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Transformers.
Hyperventilation.
X.
Zero amps.

10. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Stator windings.
5:1.
2000 watts
Two speeds

11. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
An electromagnet.
An electrical shock hazard may exist.
Second-degree burn.

12. 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.
The chest should rise or inflate.
7 -630 volts.
5:1.

13. A control power transformer...
Isolation transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
5:1
Provides single-phase power to smaller loads such as lights - heaters - etc.

14. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Lower current and higher voltage.
25 feet.
Short-circuited after power has been removed.
Capacitance.

15. A transformer has a primary voltage of 2 -800 volts and a secondary reading of 140 volts. If there are 2000 turns on the primary - how many turns are on the secondary?
Zero amps.
480 volts.
100 turns.
5:1.

16. 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.
Lower current and higher voltage.
Transformers.
A device used to store electrical energy.

17. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The motor rotation is reversed.
Derive a neutral for grounding purposes.
A step-up transformer.

18. 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?
Squirrel-cage induction motor.
Continuous.
Stator windings.
75 turns.

19. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
100 volts.
800 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

20. 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?
60 cycles per second (60 Hertz).
800 volts.
2000 watts
Potential transformer.

21. The purpose of a zig-zag transformer is to...
Nearly constant.
Derive a neutral for grounding purposes.
Grounded phase and ground fault devices were not operating.
Squirrel-cage induction motor.

22. The property of an electric circuit that opposes any change in current is called...
Derive a neutral for grounding purposes.
Inductance.
A step-up transformer.
Circuit Breaker.

23. Which of the following does a squirrel cage induction motor have?
The current will read zero.
The chest should rise or inflate.
Stator windings.
Larger than that found in the primary winding.

24. Operating coils - motors - transformers - relays and solenoids depend upon...
12 to 15 times a minute.
600 volts.
Electro-magnetism for their operation.
150 turns.

25. 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?
The motor rotation is reversed.
The chest should rise or inflate.
Squirrel-cage induction motor.
75 turns.

26. Three-phase AC underground cables must be provided with overcurrent protection using a...
100 volts.
Circuit Breaker.
Draw less current.
480 volts.

27. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
600 volts.
Hyperventilation.
200 volts AC.
A grounding resistor.

28. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Disconnect the frame-grounding conductor.
Draw less current.
The chest should rise or inflate.
A grounding resistor.

29. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
60 Hertz
Derive a neutral for grounding purposes.
No.6 AWG.
Inductance.

30. A burn causing a blister is classified as a...
Isolation transformer.
Shunted and taped
Second-degree burn.
Four times less than that of the secondary.

31. Compared to the secondary of a loaded - step-down transformer - the primary has...
H terminals.
Check to make sure that the victim is not still in contact with the electricity.
Grounded phase and ground fault devices were not operating.
Lower current and higher voltage

32. 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...
H terminals.
Draw less current.
2000 watts
Capacitance.

33. The size of a transformer is measured in...
60 cycles per second (60 Hertz).
150 turns.
Kilovolt ampere (KVA).
The capacitors should be discharged.

34. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
At the source transformer.
15 feet off the ground.
It provides good speed control.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

35. 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.
Second-degree burn.
X.
Draw less current.

36. What value of voltage will be measured from phase-to-phase - in a wye-connected secondary - if 2 -300 volts is measured from phase-to-ground?
Clamp-on ammeter.
25 feet.
150 turns.
3 -979 Volts.

37. Current transformers - or CT's - are used to...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Tied together
7 -630 volts.

38. At what rate should mouth-to-mouth resuscitation be applied?
277 volts.
12 to 15 times a minute.
Because less current flowing at high voltage causes less line loss per kilowatt.
Cut around clothing that has adhered to the burned area.

39. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
600 volts.
They should be made by the same manufacturer.
Potential transformer.
480 volts.

40. The standard frequency of alternating current used at a mine is...
75 turns.
60 Hertz
The motor rotation is reversed.
Current that changes constantly in magnitude and periodically in direction.

41. What is the danger when working around capacitors?
Lower current and higher voltage
An electrical shock hazard may exist.
Lower current and higher voltage.
It provides good speed control.

42. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
5:1
They should be made by the same manufacturer.
Larger than that found in the primary winding.
The capacitors should be discharged.

43. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Lower current and higher voltage.
Two speeds
Four times less than that of the secondary.
Transformer

44. Current that changes periodically in direction is...
Short-circuited after power has been removed.
Alternating current.
75 turns.
Isolation transformer.

45. How should clothing be removed from a burn?
Transformers.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Cut around clothing that has adhered to the burned area.
Carotid pulse - which is located in the neck next to the Adam's apple.

46. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The sum of the two capacitors.
600 volts.

47. A transformer with a 1:1 ratio is usually a (an)...
They must be installed at least 7 feet above the ground.
Isolation transformer.
150 turns.
5:1.

48. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
200 volts AC.
The current will read zero.
No.6 AWG.

49. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Transformers.
Zero amps.

50. What steps up or steps down AC voltage?
Transformer
Full-load - three-phase voltage.
Zero amps.
Lower current and higher voltage.