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. 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...
Zero amps.
Draw less current.
Check to make sure that the victim is not still in contact with the electricity.
The motor rotation is reversed.

2. How do you change the direction of a 3-phase AC motor?
5:1.
A step-up transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Reverse any two-phase leads.

3. 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.
Kilovolt ampere (KVA).
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
25 feet.

4. The primary leads of a single-phase transformer should be connected to the...
H terminals.
Continuous.
Inductance.
Grounded phase and ground fault devices were not operating.

5. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Circuit Breaker.
Clamp-on ammeter.
Disconnect the frame-grounding conductor.
277 volts.

6. 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?
15 feet off the ground.
The chest should rise or inflate.
Isolation transformer.
100 turns.

7. High voltage is used to transmit power over long distances...
60 cycles per second (60 Hertz).
Check to make sure that the victim is not still in contact with the electricity.
A step-up transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.

8. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Tied together
5:1.
A grounding resistor.
Four times less than that of the secondary.

9. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Shunted and taped
A step-up transformer.
Zero amps.
5:1.

10. All transformers step voltage up or down by...
A grounding resistor.
Alternating current.
Inductance.
75 turns.

11. At what rate should mouth-to-mouth resuscitation be applied?
Shunted and taped
Because less current flowing at high voltage causes less line loss per kilowatt.
12 to 15 times a minute.
150 turns.

12. Not true about AC power?
It provides good speed control.
Lower current and higher voltage
Shunted and taped
Circuit Breaker.

13. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
No.6 AWG.
A.C.
An electrical shock hazard may exist.

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

15. 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?
Electro-magnetism for their operation.
150 turns.
At least two phases
Disconnect the frame-grounding conductor.

16. Current that changes periodically in direction is...
Transformers.
Alternating current.
Larger than that found in the primary winding.
Shunted and taped

17. The primary function of a power transformer is to provide...
277 volts.
150 turns.
Full-load - three-phase voltage.
5:1.

18. Current in an AC circuit may be measured by...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Clamp-on ammeter.
1 amp.
Reverse any two-phase leads.

19. 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?
They should be made by the same manufacturer.
600 volts.
75 turns.
Shunted and taped

20. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
Reverse any two-phase leads.
H terminals.
A.C.

21. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
5:1.
Lower current and higher voltage
No.6 AWG.
The chest should rise or inflate.

22. How should clothing be removed from a burn?
An electromagnet.
60 Hertz
Cut around clothing that has adhered to the burned area.
100 volts.

23. What is the first step to be followed in aiding a victim of electrical shock?
An electromagnet.
Check to make sure that the victim is not still in contact with the electricity.
Full-load - three-phase voltage.
Hyperventilation.

24. 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.
5:1
277 volts.
Stator windings.
The chest should rise or inflate.

25. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
2000 watts
60 Hertz
The capacitors should be discharged.
They must be installed at least 7 feet above the ground.

26. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Second-degree burn.
X.
Grounded phase and ground fault devices were not operating.
277 volts.

27. The property of an electrical circuit that opposes any change in voltage is called...
Two speeds
5:1.
Capacitance.
Current changing constantly in magnitude and periodically in direction.

28. What type of 3-phase AC motor is used most often around a mine?
Continuous.
1 amp.
Reverse its rotation.
Squirrel-cage induction motor.

29. The property of an electric circuit that opposes any change in current is called...
Larger than that found in the primary winding.
The current will read zero.
12 to 15 times a minute.
Inductance.

30. The combined capacitance of two capacitors in parallel is...
Inductance.
They must be installed at least 7 feet above the ground.
The sum of the two capacitors.
Lower current and higher voltage

31. 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?
Kilovolt ampere (KVA).
3 -979 Volts.
Check to make sure that the victim is not still in contact with the electricity.
15 feet off the ground.

32. 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.
The current will read zero.
Isolation transformer.
Two speeds

33. 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?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
3 -979 Volts.
75 turns.
480 volts.

34. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Squirrel-cage rotor.
3 -979 Volts.
At the source transformer.

35. Three-phase AC underground cables must be provided with overcurrent protection using a...
150 turns.
Derive a neutral for grounding purposes.
Circuit Breaker.
Reverse any two-phase leads.

36. If any two-phase wires are reversed on a three-phase motor - the motor will...
H terminals.
Because less current flowing at high voltage causes less line loss per kilowatt.
Lower current and higher voltage.
Reverse its rotation.

37. 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.
Grounded phase and ground fault devices were not operating.
Carotid pulse - which is located in the neck next to the Adam's apple.
Kilovolt ampere (KVA).

38. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
Isolation transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Carotid pulse - which is located in the neck next to the Adam's apple.

39. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
7 -630 volts.
A.C.
25 feet.

40. A solenoid coil is...
An electromagnet.
Full-load - three-phase voltage.
Clamp-on ammeter.
Short-circuited after power has been removed.

41. Current transformers - or CT's - are used to...
No.6 AWG.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
75 turns.
The current will read zero.

42. Compared to the secondary of a loaded - step-down transformer - the primary has...
800 volts.
3 -979 Volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Lower current and higher voltage

43. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Zero amps.
An electrical shock hazard may exist.
60 cycles per second (60 Hertz).

44. When not connected to a load - the secondary leads of a current transformer should be...
The current will read zero.
A device used to store electrical energy.
Shunted and taped
100 volts.

45. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
60 Hertz
Four times less than that of the secondary.
Full-load - three-phase voltage.
Lower current and higher voltage.

46. Where should grounding resistors be located?
Stator windings.
The motor rotation is reversed.
At the source transformer.
Reverse any two-phase leads.

47. The standard frequency of alternating current used at a mine is...
Full-load - three-phase voltage.
A device used to store electrical energy.
60 Hertz
480 volts.

48. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
100 turns.
Hyperventilation.
They should be made by the same manufacturer.
It provides good speed control.

49. Operating coils - motors - transformers - relays and solenoids depend upon...
Carotid pulse - which is located in the neck next to the Adam's apple.
Draw less current.
Electro-magnetism for their operation.
It provides good speed control.

50. Which of the following does a squirrel cage induction motor have?
Stator windings.
Capacitance.
Check to make sure that the victim is not still in contact with the electricity.
25 feet.